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What's Included (All 12 Questions):

• Q1 - All 4 acid-base theories (Arrhenius, Bronsted-Lowry, Lewis, Solvent System) with comparison table
• Q2 - All 5 types of intermolecular forces with strength ranking and examples
• Q3 - Definitions of BP, MP, solubility + full detailed note on dipole moment (formula, geometry effects, applications)
• Q4 - Isomerism classification tree + all 6 types of structural isomerism with structural examples

• Q1 - Organic chemistry definition, Wohler's experiment, classification tree (acyclic/cyclic/aromatic) + functional group table
• Q2 - Full IUPAC rules for aldehydes (-al suffix) and amines (-amine suffix) with 8+ examples each
• Q3 - Complete free radical mechanism (Initiation→Propagation→Termination) for HBr addition to alkene + chlorination of methane
• Q4 - Stability order of radicals, hyperconjugation explanation, BDE table, chlorination vs bromination selectivity

• Q1 - SN2 mechanism with transition state, Walden inversion diagram, energy profile, all 5 factors
• Q2 - SN1 two-step mechanism, carbocation intermediate, racemization explanation, all factors, SN1 vs SN2 comparison table
• Q3 - Nucleophiles (types + nucleophilicity trends), leaving groups (ranking), steric hindrance (effect on SN2, beta-branching)
• Q4 - Carbocation structure, stability scale, hydride shift and methyl shift with mechanisms, neopentyl rearrangement example

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🧪 ORGANIC CHEMISTRY — COMPLETE EXAM ANSWERS

Units 4, 5 & 6 | University Level | 10 Marks Each

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═══════════════════════════════════════

✦ UNIT 4 — ELIMINATION REACTIONS

═══════════════════════════════════════

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Q1. Kinetics and Mechanism of E1 Reaction (10 Marks)

Definition

E1 = Elimination, Unimolecular A two-step elimination reaction in which the rate depends only on the substrate (first order kinetics). A carbocation intermediate is formed.

Rate = k [substrate]      ← First order (unimolecular)

---

General Reaction

         H   LG                    
         |   |          Base        
     —C—C—      ──────────→    C = C    +   H-Base   +   LG⁻
         |   |                (alkene)
         
Substrate loses H and LG from adjacent carbons → double bond forms

---

Mechanism of E1 (Two Steps)

---

Step 1: IONIZATION (Slow - Rate Determining Step)

         Br
          |
 CH₃—C—CH₃    slow    CH₃—C⁺—CH₃    +    Br⁻
          |    ─────→        |
         CH₃               CH₃
 (tert-butyl bromide)   (tertiary carbocation)

This step requires energy; only the substrate is involved.
Rate depends ONLY on this step.

Step 2: PROTON LOSS (Fast)

      CH₃                    CH₃
       |                      ‖
 CH₃—C⁺   +  Base  ─────→  CH₂=C     +   H-Base
       |                      |
      CH₃                    CH₃
(carbocation)              (2-methylpropene)

Base (or even solvent) removes a proton from adjacent carbon (β-carbon)
→ electrons shift to form π bond

---

Energy Profile of E1

Energy
  ^
  |         ‡₁                ‡₂
  |        /  \              / \
  |       /    \            /   \
  |      /   Carbo-\──────/     \
  |─────/    cation  intermediate \────
  Reactants                      Products
            Two transition states
            Carbocation = intermediate

---

Kinetics of E1

E1 is FIRST ORDER:

Rate = k[R-X]

Doubling substrate → doubles rate
Doubling base → NO effect on rate (base acts AFTER RDS)

This is diagnostic for E1 mechanism.

---

Stereochemistry of E1

• No strict stereochemical requirement
• The carbocation is planar → base can remove H from either face
• Gives a mixture of E and Z alkene isomers
• More stable alkene (usually E/trans) is the major product (Zaitsev's rule)

---

Zaitsev's Rule (Applied to E1)

In E1 elimination, the more substituted (more stable) alkene is the major product.

Example: 2-Bromobutane → E1

         Br
          |
  CH₃—CH—CH₂—CH₃    →   CH₃—CH=CH—CH₃   +   CH₂=CH—CH₂CH₃
                        (2-butene - major)    (1-butene - minor)
                        More substituted       Less substituted

---

Factors Affecting E1

---

E1 vs SN1 (Both have carbocation intermediate)

From same carbocation:
        ↗ SN1 (nucleophile attacks C⁺)
R⁺   
        ↘ E1  (base removes adjacent H)

Temperature: High temp → E1 favored
Nucleophile: Strong Nu → SN1 favored
These reactions always COMPETE with each other.

---

Summary Flowchart

Substrate + Heat/Polar Protic Solvent
         ↓
  Step 1: LG leaves → Carbocation (RDS)
         ↓
  Step 2: Base removes β-H → π bond forms
         ↓
  Product: More substituted alkene (Zaitsev)
  Kinetics: Rate = k[substrate] (1st order)
  Stereochemistry: E + Z mixture (E major)

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Q2. Kinetics and Mechanism of E2 Reaction (10 Marks)

Definition

E2 = Elimination, Bimolecular A one-step, concerted elimination reaction. Rate depends on BOTH substrate and base (second order kinetics). No intermediate is formed.

Rate = k [substrate][Base]     ← Second order (bimolecular)

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General Reaction

         H   LG                       
         |   |           Strong Base        
     —C—C—      ─────────────────→    C=C    +   H-Base   +   LG⁻
         |   |                        
      (β-C) (α-C)         
         
Single concerted step: Base removes H, electrons shift to form π bond,
and LG leaves - all simultaneously.

---

Mechanism of E2 (One Step, Concerted)

           H
           |
  Base:  + CH₃—CH—Br    ──────────→    CH₂=CH₂  +  H-Base  +  Br⁻
  (KOH)    ↑β  ↑α                     
           
[TRANSITION STATE]:
                    ‡
        Base---H---Cβ---Cα---LG
            (all bonds breaking/forming simultaneously)

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CRITICAL REQUIREMENT: Anti-Periplanar Geometry

Newman Projection (looking along Cα—Cβ bond):

    H                    LG
    |                     |
    Cβ ──────── Cα

Anti arrangement (180° apart) = required for E2

           H
           |
    ───────────────
           |
          LG
    (H and LG anti-periplanar → E2 can proceed)

Syn-periplanar (0°) can also work but is much less common (rare cases)

---

Energy Profile of E2

Energy
  ^
  |              ‡ (single transition state)
  |             / \
  |            /   \
  |           /     \
  |──────────/       \──────────
  Reactants              Products
  
Single peak - ONE transition state
No intermediate

---

Kinetics of E2

E2 is SECOND ORDER:

Rate = k[R-X][Base]

Doubling substrate → doubles rate
Doubling base concentration → doubles rate
Both substrate AND base appear in rate equation.

This is diagnostic for E2 mechanism.

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Stereochemistry of E2

Example: Meso-2,3-dibromobutane + KOH → E2

In anti conformation:
   H and Br are anti → elimination gives → (E)-2-butene (trans)

If syn conformation were required:
   → would give (Z)-2-butene (cis) - but this requires syn-periplanar

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Regioselectivity in E2 - Zaitsev vs Hofmann

With small base (e.g., KOH, EtO⁻):
→ Zaitsev product (more substituted alkene) - MAJOR

With bulky base (e.g., t-BuOK):
→ Hofmann product (less substituted alkene) - MAJOR
(bulky base cannot access hindered β-H; attacks less hindered β-H)

Example: 2-Bromobutane + base →

With KOH:     2-butene (major, Zaitsev)
With t-BuOK:  1-butene (major, Hofmann)

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Factors Affecting E2

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E2 vs E1 - Comparison Table

┌─────────────────┬────────────────────────┬────────────────────────┐
│ Feature         │ E1                     │ E2                     │
├─────────────────┼────────────────────────┼────────────────────────┤
│ Steps           │ 2 (stepwise)           │ 1 (concerted)          │
│ Rate law        │ k[substrate]           │ k[substrate][base]     │
│ Order           │ 1st order              │ 2nd order              │
│ Intermediate    │ Carbocation            │ None (only TS)         │
│ Base needed     │ Weak base OK           │ Strong base needed     │
│ Best substrate  │ Tertiary               │ 2° and 3°              │
│ Stereochemistry │ E+Z mixture            │ Anti-periplanar (E2)   │
│ Rearrangement   │ Yes (cation forms)     │ No                     │
│ Regiosel.       │ Zaitsev (more subst.)  │ Zaitsev or Hofmann     │
│ Solvent         │ Polar protic           │ Either                 │
└─────────────────┴────────────────────────┴────────────────────────┘

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Q3. Solvent Effects, Orientation and Reactivity in E1 and E2 (10 Marks)

A. Solvent Effects

┌─────────────────────────────────────────────────────────┐
│ Polar PROTIC solvents (H₂O, EtOH, AcOH)               │
│ → Stabilize carbocation intermediates → FAVOR E1/SN1   │
│ → Solvate ions by hydrogen bonding                     │
├─────────────────────────────────────────────────────────┤
│ Polar APROTIC solvents (DMSO, DMF, acetone)            │
│ → Cannot solvate base → base remains reactive → E2/SN2 │
├─────────────────────────────────────────────────────────┤
│ Nonpolar solvents (CCl₄, hexane)                       │
│ → Disfavor ionic mechanisms entirely                   │
└─────────────────────────────────────────────────────────┘

• E1 → Polar protic solvent (water, ethanol)
• E2 → Polar aprotic or any solvent with strong base

---

B. Orientation in Elimination (Regioselectivity)

---

Zaitsev's Rule (1875)

Elimination preferentially gives the more substituted (more stable) alkene.

More substituted = more alkyl groups on double bond carbons
More stable = lower energy (more hyperconjugation)

Example: 2-Bromobutane
    Br
    |
CH₃—CH—CH₂—CH₃

β-H removal from C1: → 1-Butene (CH₂=CHCH₂CH₃) - less substituted
β-H removal from C3: → 2-Butene (CH₃CH=CHCH₃) - MORE substituted ← MAJOR

Zaitsev product = 2-Butene

---

Hofmann's Rule

With bulky bases, elimination gives the less substituted (less hindered) alkene.

Bulky bases: (CH₃)₃CO⁻K⁺ (potassium tert-butoxide)

The bulky base CANNOT get close to hindered β-H
→ attacks only the least hindered β-H
→ gives less substituted alkene

Example: 2-Bromobutane + t-BuOK →
→ 1-Butene (MAJOR) ← less substituted but less hindered

---

Bredt's Rule

Elimination cannot form a double bond at a bridgehead carbon in a small bicyclic system (bridgehead alkene is too strained to form).

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C. Reactivity - E1 vs E2 vs SN1 vs SN2

Substrate type determines which mechanism dominates:

Methyl:    SN2 only (no E possible, no carbocation)
Primary:   SN2 >> E2 (little E with strong bulky base only)
Secondary: SN2 (polar aprotic, strong Nu) or E2 (strong base)
           or SN1/E1 (polar protic, weak base, heat)
Tertiary:  SN1/E1 (polar protic) or E2 (strong base, no SN2!)

HIGH temperature → FAVORS ELIMINATION (E1 or E2)
LOW temperature → FAVORS SUBSTITUTION (SN1 or SN2)

Reason: Elimination has higher activation energy (ΔS is positive
for elimination since more molecules are formed from one).

Strong base (OH⁻, RO⁻, t-BuOK) → E2 favored
Weak base (H₂O, ROH) → SN1/E1 favored
Bulky strong base (t-BuOK) → E2, Hofmann product

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D. Reactivity Summary Chart

         Substrate + Reagent → Predominant Reaction

  1° R-X + strong Nu (NaOH, NaCN):     SN2
  1° R-X + strong bulky base (t-BuOK): E2
  2° R-X + strong Nu, aprotic:         SN2
  2° R-X + strong base, heat:          E2
  2° R-X + weak Nu, protic, heat:      SN1 / E1
  3° R-X + strong base:               E2 (no SN2 possible!)
  3° R-X + weak Nu, protic:            SN1 / E1

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Q4. Elimination vs Substitution | Dehydration of Alcohol (10 Marks)

A. Elimination vs Substitution - Competition

                        LG
                         |
    Nu: / Base + R₁—C—R₂ 
                         |
                        R₃
                     ↙        ↘
         Substitution (Nu attacks C)   Elimination (Base removes β-H)
         
         R₁—C—Nu                       R₁C=R₂ (alkene)

---

┌──────────────────────┬───────────────────┬───────────────────┐
│ Condition            │ Substitution      │ Elimination       │
├──────────────────────┼───────────────────┼───────────────────┤
│ Temperature          │ Low               │ High              │
│ Base/Nucleophile     │ Weak, small Nu    │ Strong, bulky base│
│ Substrate            │ Methyl/Primary    │ Tertiary/Secondary│
│ Solvent              │ Polar aprotic     │ Polar protic      │
│ Conc. of base        │ Low               │ High              │
│ Steric hindrance     │ Less hindered     │ More hindered     │
└──────────────────────┴───────────────────┴───────────────────┘

• Strong, bulky base + high temperature + tertiary substrate = E2
• Strong, small nucleophile + polar aprotic + primary substrate = SN2
• Polar protic + tertiary + heat = E1/SN1 mixture

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B. Dehydration of Alcohols

General:
R—CH₂—CH₂—OH   ──[H⁺/H₂SO₄, heat]──→   R—CH=CH₂   +   H₂O
(alcohol)                                  (alkene)

---

• Conc. H₂SO₄ at 170°C (high temp = alkene favored)
• Conc. H₃PO₄ at 200°C
• Al₂O₃ (alumina) at 350°C
• POCl₃ in pyridine (milder, for sensitive substrates)

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Mechanism of Dehydration (E1 - for 2° and 3° Alcohols)

          OH                  OH₂⁺
           |          H⁺       |
 CH₃—C—CH₃   ─────→  CH₃—C—CH₃
           |                   |
          CH₃                 CH₃
(alcohol; OH⁻ is bad LG)   (protonated; H₂O is good LG!)

         OH₂⁺                  ⁺
          |          slow       |
 CH₃—C—CH₃   ─────→  CH₃—C—CH₃   +  H₂O
          |    (RDS)             |
         CH₃                   CH₃
                          (tertiary carbocation)

          ⁺                     
          |        fast         
 CH₃—C—CH₃   ─────→  CH₂=C—CH₃   +   H⁺
          |                     |
         CH₃                   CH₃
                          (2-methylpropene)

---

Mechanism of Dehydration (E2 - for 1° Alcohols with POCl₂/Py)

1° Alcohols: R-OH + POCl₂/Py →

Step 1: OH attacks POCl₂ → forms phosphate ester (good LG)
Step 2: Pyridine (base) removes β-H concertedly → E2
Step 3: Alkene formed + phosphate leaves

(SN2-like mechanism for primary alcohols)

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Reactivity Order for Dehydration

Ease of dehydration:
Tertiary > Secondary > Primary

3° ROH: Easy, low temperature, H₂SO₄ (E1)
2° ROH: Moderate temperature needed
1° ROH: High temperature, or special reagent (POCl₃/Py)

Reason: Stability of carbocation intermediate (for E1)
3° carbocation forms easily → 3° alcohol dehydrates most easily

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C. Assay of Dehydration (Ease of Dehydration Test)

1. Lucas Test (ZnCl₂/HCl):
   • Primary: no reaction at room temp (takes hours)
   • Secondary: turns cloudy in 5 min (SN1/dehydration)
   • Tertiary: immediate turbidity (fast dehydration/SN1)
2. Iodine number / Bromine number test: Alkene produced absorbs Br₂ → decolorizes brown Br₂/CCl₄ (confirms alkene = dehydration occurred)
3. Refractive index and boiling point change after reaction
4. IR spectroscopy: Loss of broad O-H stretch (3200-3500 cm⁻¹), appearance of C=C stretch (1620-1680 cm⁻¹)
5. GC-MS analysis: Identification of alkene product confirms dehydration

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Example: 3,3-Dimethyl-2-butanol → H₂SO₄/heat →

         OH
          |
 CH₃—CH—C(CH₃)₃  →  carbocation  →  hydride shift  →  rearranged alkene

Expected: 3,3-dimethyl-1-butene
Actual major product: 2,3-dimethyl-2-butene (after rearrangement!)

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═══════════════════════════════════════

✦ UNIT 5 — FREE RADICAL ADDITION & PEROXIDE EFFECT

═══════════════════════════════════════

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Q1. Mechanism of Free Radical Addition (10 Marks)

Introduction

Free radical addition is an addition reaction to an alkene (or alkyne) that proceeds through a free radical mechanism rather than an ionic mechanism. It involves species with unpaired electrons.

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What is a Free Radical?

A free radical is an atom, ion, or molecule with an ODD (unpaired) electron.

Examples:
Cl•    (chlorine radical)
Br•    (bromine radical)
•CH₃   (methyl radical)
RO•    (alkoxy radical from peroxide)

Notation: the dot (•) represents the unpaired electron.

---

Conditions for Free Radical Addition

1. Presence of peroxide (ROOR) as initiator
2. UV light (hν) or heat to generate radicals
3. HBr (specifically - NOT HCl or HI for peroxide effect)
4. Alkene substrate (double bond)

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General Mechanism (Three Stages)

┌──────────────────────────────────────────────────────┐
│                                                      │
│  FREE RADICAL ADDITION MECHANISM                     │
│                                                      │
│  Stage 1:  INITIATION   → Generate initial radicals  │
│                                                      │
│  Stage 2:  PROPAGATION  → Chain reaction (repeats    │
│                            thousands of times)       │
│                                                      │
│  Stage 3:  TERMINATION  → Radicals combine → stop    │
│                                                      │
└──────────────────────────────────────────────────────┘

---

STAGE 1: INITIATION

           hν or Δ
R—O—O—R  ────────→  2 R—O•     (alkoxy radicals)
(peroxide)           (two identical radicals)

Then:
R—O•  +  H—Br  →  R—O—H  +  Br•    (bromine radical generated)

A : B  →  A•  +  B•       (homolytic - equal split)
A : B  →  A⁺  +  B:⁻      (heterolytic - unequal split, ionic)

---

STAGE 2: PROPAGATION

          Br•
           ↓
  CH₃—CH=CH₂   →   CH₃—CH•—CH₂Br
  (propene)          (secondary radical - more stable)
  
  NOT:
  CH₃—CH=CH₂   →   CH₃—CHBr—CH₂•   (primary - less stable) ✗

  CH₃—CH•—CH₂Br  +  H—Br  →  CH₃—CH₂—CH₂Br  +  Br•
                               (1-bromopropane)        ↑
                                                  Br• restarts cycle

---

STAGE 3: TERMINATION

Br•  +  Br•   →  Br₂
R•   +  Br•   →  R—Br
R•   +  R•    →  R—R

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Complete Mechanism Summary

INITIATION:   ROOR →[hν]→ 2 RO•  →  Br•

PROPAGATION (cycle):
  Br• + CH₃CH=CH₂  →  CH₃CH•CH₂Br
  CH₃CH•CH₂Br + HBr → CH₃CH₂CH₂Br + Br• (repeat!)

TERMINATION:
  Radical + Radical → stable product

---

Why Anti-Markovnikov Product?

In ionic addition of HBr (no peroxide):
  H⁺ adds to less substituted C → more substituted carbocation forms
  → Br⁻ attacks more substituted C
  → MARKOVNIKOV product (2-bromopropane from propene)

In free radical addition of HBr (with peroxide):
  Br• adds to less substituted C → more substituted radical forms
  → H from HBr joins the more substituted C radical
  → ANTI-MARKOVNIKOV product (1-bromopropane from propene)

KEY: Br is the atom that adds first in BOTH cases
     Ionic: Br⁻ adds last → Markovnikov
     Radical: Br• adds first → Anti-Markovnikov

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Q2. Peroxide Effect and Markovnikov's Rule (10 Marks)

A. Markovnikov's Rule

When HX adds to an unsymmetrical alkene, the hydrogen goes to the carbon with MORE hydrogens (less substituted), and X goes to the carbon with FEWER hydrogens (more substituted).

Original statement:
"The addition of hydrogen halide to an asymmetric alkene places H
on the carbon bearing more H atoms."

H⁺ adds to carbon that gives the MORE STABLE carbocation.

CH₃—CH=CH₂  +  HBr  →  CH₃—CH⁺—CH₃  →  CH₃—CHBr—CH₃
                          (2° carbocation                 (2-Bromopropane)
                           more stable)                   MARKOVNIKOV product

1. Propene + HBr → 2-Bromopropane (Markovnikov)
   CH₃CH=CH₂ + HBr → CH₃CHBrCH₃

2. Propene + HCl → 2-Chloropropane
   CH₃CH=CH₂ + HCl → CH₃CHClCH₃

3. But-1-ene + HBr → 2-Bromobutane
   CH₃CH₂CH=CH₂ + HBr → CH₃CH₂CHBrCH₃

4. 2-Methylpropene + HBr → 2-Bromo-2-methylpropane
   (CH₃)₂C=CH₂ + HBr → (CH₃)₂CBrCH₃

• Ionic mechanism
• No peroxide
• No UV light
• HX adds to alkene

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B. Peroxide Effect (Kharasch Effect, 1933)

When HBr adds to an alkene in the presence of peroxides (or UV light), the product is the ANTI-MARKOVNIKOV addition product. This is called the peroxide effect or Kharasch effect.

CH₃CH=CH₂  +  HBr  ──────────────────→  CH₃CH₂CH₂Br
                    [peroxide/hν]         (1-Bromopropane)
                                          ANTI-MARKOVNIKOV!

---

The two propagation steps must BOTH be exothermic (energetically favorable):

Step A: X• + alkene → radical intermediate  (Br• addition - exothermic ✓)
Step B: radical + HX → product + X•          (H abstraction - exothermic ✓)

For HCl:
  Cl• addition to alkene: very exothermic (too fast, no selectivity) ✓
  R• + HCl → R-H + Cl•: ENDOTHERMIC ✗ (H-Cl bond too strong)
  → Chain does not propagate efficiently

For HI:
  I• addition to alkene: ENDOTHERMIC ✗ (I• too stable, C-I bond weak)
  → Chain does not initiate

For HBr: BOTH steps exothermic → chain propagates efficiently ✓

SUMMARY:
HCl: Step B is endothermic → no peroxide effect
HBr: Both steps exothermic → peroxide effect occurs ✓
HI:  Step A is endothermic → no peroxide effect

ONLY HBr shows anti-Markovnikov addition with peroxides.

---

┌─────────────────────────┬──────────────────────┬────────────────────────┐
│ Condition               │ Mechanism            │ Product (propene+HBr)  │
├─────────────────────────┼──────────────────────┼────────────────────────┤
│ No peroxide, dark       │ Ionic (electrophilic)│ 2-Bromopropane (Markov)│
│ With peroxide or hν     │ Free radical         │ 1-Bromopropane (Anti-M)│
└─────────────────────────┴──────────────────────┴────────────────────────┘

---

C. Mechanism Behind the Selectivity

IONIC: H⁺ adds first → carbocation intermediate controls orientation
RADICAL: Br• adds first → carbon radical intermediate controls orientation

In radical:
Br• adds to CH₂ end (less substituted) to give secondary radical:
CH₃—CH•—CH₂Br   (2° radical - MORE stable) → MAJOR pathway

If Br• added to CH end (more substituted):
CH₃•—CHBr—CH₂  wait... CH₃—CHBr—CH₂• (1° radical - LESS stable) → MINOR

---

Q3. Mechanism of Peroxide-Initiated Addition of Hydrogen Bromide (10 Marks)

Full Detailed Mechanism

---

Reagents:

• Propene: CH₃—CH=CH₂
• HBr: H—Br
• Benzoyl peroxide: (C₆H₅COO)₂ [initiator]

---

STAGE 1: INITIATION

       O   O                  O
       ‖   ‖       hν or Δ    ‖
C₆H₅—C—O—O—C—C₆H₅  ────────→  2 C₆H₅—C—O•
(benzoyl peroxide)              (benzoyloxy radical)

Bond broken: O—O bond (weakest bond in peroxide)

    O
    ‖
C₆H₅—C—O•   →   C₆H₅•   +   CO₂
(benzoyloxy)   (phenyl radical)

C₆H₅—C(=O)—O•  +  H—Br  →  C₆H₅—C(=O)—OH  +  Br•
(or C₆H₅• + HBr → C₆H₆ + Br•)

---

STAGE 2: PROPAGATION

              Br•
              |
  CH₃—CH=CH₂  →   CH₃—CH•—CH₂—Br
  (propene)         
              ↑
    Br• attacks CH₂ end (less substituted)
    → Gives SECONDARY carbon radical (CH at position 2)
    → More stable than primary (anti-Markovnikov selectivity)

  CH₃—CH•—CH₂Br  +  H—Br  →  CH₃—CH₂—CH₂Br  +  Br•
  (radical)          (HBr)     (1-bromopropane)    ↑
                                                 Br• regenerated
                                                 → cycle continues

---

STAGE 3: TERMINATION

Br•  +  Br•   →   Br₂        (bromine gas)
Br•  +  R•    →   R—Br       (alkyl bromide)
R•   +  R•    →   R—R        (coupled alkane)

---

Energy Diagram for Each Propagation Step

Propagation Step 1 (Br• + propene):
  Exothermic: ΔH = -2 kcal/mol   (slight exotherm)

Propagation Step 2 (R• + HBr):
  Exothermic: ΔH = -12 kcal/mol  (more exothermic)

Both steps EXOTHERMIC → chain propagates → reaction proceeds efficiently

---

Product and Stereochemistry

Final Product: CH₃CH₂CH₂Br = 1-Bromopropane (Anti-Markovnikov)

Compare with ionic:
CH₃CHBrCH₃ = 2-Bromopropane (Markovnikov)

---

Key Points to Remember

1. Peroxide initiates the chain reaction by generating Br•
2. Br• always adds to LESS substituted carbon of alkene
3. More stable (secondary/tertiary) carbon radical forms
4. Product is ANTI-MARKOVNIKOV
5. Only HBr shows this effect (both propagation steps must be exothermic)
6. Chain length = 10,000+ cycles before termination
7. Inhibitors (O₂, hydroquinone) stop the chain at initiation/propagation

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Q4. Mechanism of Halogenation & Orientation in Free Radical Addition (10 Marks)

A. Mechanism of Free Radical Halogenation

General: R—H  +  X₂  ──hν/Δ──→  R—X  +  H—X

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Mechanism of Chlorination of Methane (Classic Example)

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Cl—Cl   ──hν──→   Cl•  +  Cl•
(chlorine gas)       (chlorine radicals - homolytic cleavage)

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Step A: Cl• abstracts H from methane

   Cl•  +  H—CH₃   →   H—Cl   +   •CH₃
   (chlorine radical)    (HCl)   (methyl radical)
   
Step B: Methyl radical reacts with Cl₂

   •CH₃  +  Cl—Cl   →   CH₃—Cl  +  Cl•
   (methyl radical)      (chloromethane)  ↑
                                       Cl• restarts cycle!

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Cl•  +  Cl•   →  Cl₂
•CH₃  +  Cl•  →  CH₃Cl
•CH₃  +  •CH₃ →  C₂H₆     (ethane as side product)

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Further Halogenation (Multiple Substitution)

CH₄ →[Cl₂/hν]→ CH₃Cl →[Cl₂/hν]→ CH₂Cl₂ →[Cl₂/hν]→ CHCl₃ →[Cl₂/hν]→ CCl₄

Product mixture obtained unless excess CH₄ is used.
To get predominantly CH₃Cl: use large excess of CH₄.

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B. Orientation in Free Radical Addition to Alkenes

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For CH₃—CH=CH₂ (propene) + Br•:

Option 1: Br• attacks C1 (CH₂ end)
  → CH₃—CH•—CH₂Br  (SECONDARY radical at C2) ← MORE STABLE ✓

Option 2: Br• attacks C2 (CH end)
  → CH₃—CHBr—CH₂•  (PRIMARY radical at C3) ← LESS STABLE ✗

Orientation controlled by: STABILITY OF RADICAL INTERMEDIATE

Radical stability: 3° > 2° > 1° > Methyl

→ Radical adds to give the most stable (most substituted) radical
→ Since radical adds to LESS substituted C → Anti-Markovnikov product

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Orientation with Different Alkenes

CH₂=CH₂  +  Br•  →  •CH₂—CH₂Br  (only one option - symmetric)
→ No regioselectivity issue

Example 1: Isobutylene (CH₂=C(CH₃)₂) + Br•

  Br• at CH₂ end → (CH₃)₂C•—CH₂Br  (TERTIARY radical) ← MAJOR ✓
  Br• at C(CH₃)₂ end → (CH₃)₂CBr—CH₂•  (PRIMARY radical) ✗

Product: (CH₃)₂CHCH₂Br (anti-Markovnikov)

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Orientation in Allylic Radical Addition

CH₂=CH—CH₃ + Br• (at high temp = NBS reaction)
→ Allylic radical: CH₂=CH—CH₂•  ↔  •CH₂—CH=CH₂
                   (resonance delocalized)
→ Br adds at both ends: mixture of allylic bromides

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Reactivity of Halogens in Free Radical Addition

Reactivity (toward C-H abstraction):
F• > Cl• > Br• > I•
(most reactive)    (least reactive)

Selectivity (preference for weaker C-H bonds):
I• > Br• > Cl• > F•
(most selective)   (least selective)

Reactivity and selectivity are INVERSELY related.

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═══════════════════════════════════════

✦ UNIT 6 — FREE RADICAL REACTIONS (ADVANCED)

═══════════════════════════════════════

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Q1. Mechanism of Free Radical Halogenation of Alkenes (10 Marks)

Two Types of Free Radical Reactions with Alkenes

1. ALLYLIC HALOGENATION (substitution at allylic C-H)
   → Occurs at HIGH temperature or with NBS (N-Bromosuccinimide)
   → Halogen replaces allylic H

2. ADDITION HALOGENATION (addition across C=C)
   → Occurs at LOW temperature
   → Halogen adds across the double bond

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A. Allylic Halogenation with NBS

        O  O
        ‖  ‖
   N—Br  (NBS)
        |
     succinimide ring

Used for: selective allylic bromination
Conditions: CCl₄ solvent, hν or ROOR initiator

Step 1: INITIATION
NBS + hν → succinimide radical + Br•
(or ROOR → RO• → + HBr from trace HBr → Br•)

Step 2: PROPAGATION

  Br• + [cyclohexene]  →  [cyclohexenyl radical] + HBr
                           (allylic radical - resonance stabilized!)
  
  [cyclohexenyl radical] + Br₂(from NBS)  →  3-Bromocyclohexene + Br•

Step 3: TERMINATION
  Two radicals combine.

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Allylic C-H bond is WEAKER than regular C-H:

  Allylic C-H BDE: ~88 kcal/mol
  Normal C-H BDE:  ~100 kcal/mol

Weaker bond = easier to break = more reactive toward radical abstraction

ALSO: Allylic radical is STABILIZED by resonance:
       •
  C=C—CH₂  ↔  C=C with resonance
  
So: Br• preferentially abstracts allylic H → allylic radical forms
Then: Br₂ (from NBS) brominates the radical → product

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B. Mechanism - Free Radical Addition of Cl₂ to Alkene (at Low Temp)

Cl₂  ──hν──→  2 Cl•   (initiation)

Cl•  +  CH₂=CH₂  →  •CH₂—CH₂Cl   (Cl• adds to ethene)
•CH₂—CH₂Cl  +  Cl₂  →  ClCH₂—CH₂Cl  +  Cl•   (propagation)

Product: 1,2-dichloroethane

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C. Mechanism - Free Radical Addition of Br₂ to Alkene

Br₂  ──hν──→  2 Br•   (initiation)

Br•  +  CH₃CH=CH₂  →  CH₃CH•CH₂Br  (secondary radical)
CH₃CH•CH₂Br  +  Br₂  →  CH₃CHBrCH₂Br  +  Br•

Product: 1,2-dibromopropane

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D. Low Temperature vs High Temperature - Orientation Difference

LOW temperature (below -80°C for Cl₂/alkene):
→ ADDITION across the double bond → 1,2-dihalide

HIGH temperature (above 300°C for Cl₂/propene):
→ SUBSTITUTION at allylic position → allyl chloride
→ Addition is reversible at high temp, substitution is irreversible

CH₂=CH—CH₃ + Cl₂:
  Low temp:  → CH₂Cl—CHCl—CH₃ (1,2-dichloropropane - addition)
  High temp: → CH₂=CH—CH₂Cl  (allyl chloride - allylic substitution)

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Q2. Nucleophilic Substitution in Allylic Substrates (10 Marks)

Introduction

General structure:
C=C—C—LG     (LG at allylic carbon)
      ↑
  allylic carbon

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Why Allylic Systems are Special

Allyl carbocation:
   ⁺
  C=C—CH₂   ↔   C=C—CH₂
             ↕
       +charge delocalized over two carbons → STABLE

Allyl radical:
   •
  C=C—CH₂   ↔   C=C—CH₂ 
                       •
       Radical delocalized → STABLE

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SN1 Reaction in Allylic Systems

1. Allylic carbocation forms easily (resonance-stabilized)
2. Low energy needed for ionization

Example: Crotyl chloride + H₂O

CH₃—CH=CH—CH₂Cl  ──SN1──→  CH₃—CH=CH—CH₂⁺  ↔  CH₃—CH⁺—CH=CH₂
                              (crotyl cation: delocalized)

Attack by H₂O at EITHER end of delocalized cation:
→  CH₃—CH=CH—CH₂OH  (crotyl alcohol)      ← direct attack
→  CH₃—CH(OH)—CH=CH₂  (methylvinylcarbinol) ← attack at other end

BOTH products form = allylic rearrangement (SN1')

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SN2 Reaction in Allylic Systems

Nu:  +  CH₂=CH—CH₂—X  →  Nu—CH₂—CH=CH₂  +  X⁻
       (backside attack at allylic C)

Nu:  +  CH₂=CH—CH₂—X  →  Nu—CH₂—CH=CH₂
         (allylic system)   (product with double bond shifted)

In SN2': 
Nu attacks γ-carbon while LG leaves from α-carbon
→ double bond migrates
This is called "SN2' " (allylic displacement with rearrangement)

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Factors Controlling SN1' vs SN2 vs SN2' in Allylic Systems

┌────────────────────┬──────────────────────────────────────┐
│ Condition          │ Mechanism                            │
├────────────────────┼──────────────────────────────────────┤
│ Polar protic       │ SN1 / SN1' (carbocation pathway)    │
│ Strong Nu, aprotic │ SN2 (direct) or SN2' (rearranged)   │
│ Secondary allylic  │ Mix of SN1' and SN2'                 │
│ Primary allylic    │ SN2 (direct) preferred               │
│ Tertiary allylic   │ SN1' exclusively                     │
└────────────────────┴──────────────────────────────────────┘

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Allylic Rearrangement (1,3-Shift in SN1')

Classic example: 1-chloro-2-butene + AgNO₃/EtOH →

CH₃—CH=CH—CH₂Cl  →  [CH₃—CH=CH—CH₂⁺ ↔ CH₃—CH⁺—CH=CH₂]
(crotyl chloride)         (delocalized allylic cation)
                                    ↓ EtOH attacks both ends
                     CH₃—CH=CH—CH₂OEt    +    CH₃—CH(OEt)—CH=CH₂
                     (direct product)          (rearranged product)

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Q3. Orientation and Reactivity in Free Radical Addition to Conjugated Dienes (10 Marks)

What are Conjugated Dienes?

C=C—C=C    (conjugated diene - 1,3-diene)
1 2 3 4

Examples:
1,3-Butadiene:   CH₂=CH—CH=CH₂
1,3-Cyclohexadiene (ring)
Isoprene: CH₂=C(CH₃)—CH=CH₂

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Special Properties of Conjugated Dienes

1. More stable than isolated dienes
2. Undergo 1,2-addition and 1,4-addition
3. Form allylic radical/carbocation intermediates

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Free Radical Addition to Conjugated Dienes

CH₂=CH—CH=CH₂  +  HBr  ─[peroxide/hν]→  Products
(1,3-butadiene)

1,2-Addition product (direct addition):
   CH₂=CH—CH=CH₂  +  HBr  →  CH₂=CH—CHBr—CH₃
                                (3-bromo-1-butene)

1,4-Addition product (conjugate addition):
   CH₂=CH—CH=CH₂  +  HBr  →  BrCH₂—CH=CH—CH₃
                                (1-bromo-2-butene)

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Mechanism of 1,2 and 1,4 Addition

         Br•
          ↓
CH₂=CH—CH=CH₂  →  BrCH₂—CH•—CH=CH₂   (radical at C2)
                        ↕ resonance
                   BrCH₂—CH=CH—CH₂•    (radical at C4)
                   (delocalized allylic radical)

H at C2: BrCH₂—CH₂—CH=CH₂   (1,2-product at C2) ← confusing, reclarify below
H at C4: BrCH₂—CH=CH—CH₃    (1,4-product at C4)  ← 1,4-addition

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Br• attacks C1:
  BrCH₂—CH•—CH=CH₂  ↔  BrCH₂—CH=CH—CH₂•

H• (from HBr) attacks:
  C2 radical → BrCH₂—CH₂—CH=CH₂   = 3-bromo-1-butene (1,2-add)
  C4 radical → BrCH₂—CH=CH—CH₃    = 1-bromo-2-butene (1,4-add)

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Temperature Dependence (Thermodynamic vs Kinetic Control)

┌────────────────────┬──────────────────────────────────────────┐
│ Condition          │ Major Product                            │
├────────────────────┼──────────────────────────────────────────┤
│ Low temperature    │ 1,2-addition product (KINETIC control)   │
│ (-80°C)            │ Forms faster (lower Ea), less stable     │
├────────────────────┼──────────────────────────────────────────┤
│ High temperature   │ 1,4-addition product (THERMODYNAMIC)     │
│ (40-60°C)          │ More stable (conjugated alkene in product)│
└────────────────────┴──────────────────────────────────────────┘

1,4-product: BrCH₂—CH=CH—CH₃  (internal alkene, more stable)
1,2-product: CH₂=CH—CHBr—CH₃  (terminal alkene, less stable)

At low T: Kinetic product (1,2) forms faster → frozen in
At high T: Equilibrium reached → more stable 1,4 product dominates

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Reactivity of Conjugated vs Isolated Dienes

Conjugated dienes are MORE REACTIVE than isolated dienes because:

1. Delocalized π system → easier for radical/electrophile to attack
2. Allylic radical intermediate (stabilized by resonance) forms easily
3. Lower activation energy for addition

1,3-Butadiene > 1,4-Pentadiene  (conjugated > isolated, reactivity)

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Diels-Alder Reaction (Bonus - conjugated dienes)

Conjugated dienes undergo [4+2] cycloaddition with dienophile:
diene + dienophile → cyclohexene (stereospecific)
This is NOT a free radical reaction but shows unique reactivity of conjugated dienes.

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Q4. Comparison - Free Radical Substitution vs Free Radical Addition (10 Marks)

Introduction

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Definition

A reaction in which a hydrogen atom (or other atom) on an alkane or allylic/benzylic position is replaced by a halogen atom via a free radical mechanism.

A reaction in which atoms are added across a double bond of an alkene or alkyne via a free radical mechanism.

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Comparison Table

┌────────────────────┬─────────────────────────────┬──────────────────────────────┐
│ Feature            │ Free Radical SUBSTITUTION   │ Free Radical ADDITION        │
├────────────────────┼─────────────────────────────┼──────────────────────────────┤
│ Substrate          │ Alkanes (C-H bonds)          │ Alkenes/Alkynes (C=C bonds)  │
│                    │ Allylic/benzylic C-H          │                              │
├────────────────────┼─────────────────────────────┼──────────────────────────────┤
│ Bond broken        │ C-H bond (σ bond)            │ C=C bond (π bond)            │
├────────────────────┼─────────────────────────────┼──────────────────────────────┤
│ Bond formed        │ C-X bond (new σ bond)        │ Two new σ bonds              │
│                    │ H-X bond (by-product)        │ (C-X and C-H or C-C)         │
├────────────────────┼─────────────────────────────┼──────────────────────────────┤
│ Net result         │ R-H → R-X + H-X             │ C=C → C-C (saturated)        │
│                    │ (substitution of H by X)     │ (double bond consumed)       │
├────────────────────┼─────────────────────────────┼──────────────────────────────┤
│ Reagents           │ X₂ (Cl₂ or Br₂)             │ HBr + peroxide               │
│                    │ NBS (for allylic)            │ Br₂ or Cl₂ + hν              │
├────────────────────┼─────────────────────────────┼──────────────────────────────┤
│ Conditions         │ UV light or high temp         │ Peroxide or UV light         │
│                    │ Gas phase preferred           │ Solution phase               │
├────────────────────┼─────────────────────────────┼──────────────────────────────┤
│ Initiator          │ hν or Δ (directly on X₂)    │ ROOR (peroxide) or hν        │
├────────────────────┼─────────────────────────────┼──────────────────────────────┤
│ Initiation step    │ X₂ → 2X•                    │ ROOR → RO• → Br•             │
├────────────────────┼─────────────────────────────┼──────────────────────────────┤
│ Propagation Step 1 │ X• + R-H → HX + R•          │ X• + C=C → X-C-C•           │
│ Propagation Step 2 │ R• + X₂ → R-X + X•          │ X-C-C• + HX → product + X•  │
├────────────────────┼─────────────────────────────┼──────────────────────────────┤
│ Key intermediate   │ Carbon radical (R•)          │ Carbon radical (allylic/     │
│                    │ (more stable 3°>2°>1°)       │ secondary/tertiary)          │
├────────────────────┼─────────────────────────────┼──────────────────────────────┤
│ Orientation        │ Attack on weakest C-H bond   │ Radical adds to give most    │
│                    │ (3°C-H most reactive)        │ stable radical (anti-Markov.)│
├────────────────────┼─────────────────────────────┼──────────────────────────────┤
│ Selectivity        │ Br: high selectivity         │ Br: anti-Markovnikov only    │
│                    │ Cl: low selectivity          │ Cl: low selectivity          │
├────────────────────┼─────────────────────────────┼──────────────────────────────┤
│ Product            │ Alkyl halide (R-X)           │ Anti-Markovnikov product     │
│                    │ (mixture at different C)     │ (1-haloalkane from terminal  │
│                    │                              │  alkene)                     │
├────────────────────┼─────────────────────────────┼──────────────────────────────┤
│ Termination        │ R• + X• → R-X               │ Same: radicals combine       │
│                    │ X• + X• → X₂                │                              │
├────────────────────┼─────────────────────────────┼──────────────────────────────┤
│ Chain length       │ Short (300-10,000 cycles)    │ Very long (10,000-100,000)   │
├────────────────────┼─────────────────────────────┼──────────────────────────────┤
│ Example            │ CH₄+Cl₂→CH₃Cl+HCl           │ CH₃CH=CH₂+HBr→CH₃CH₂CH₂Br  │
└────────────────────┴─────────────────────────────┴──────────────────────────────┘

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Mechanism Comparison (Schematic)

FREE RADICAL SUBSTITUTION:                FREE RADICAL ADDITION:

INITIATION:                               INITIATION:
X₂ → 2X•                                 ROOR → 2RO• → 2Br•

PROPAGATION:                              PROPAGATION:
X• + R-H → HX + R•  (H abstraction)     Br• + C=C → BrC-C•  (addition)
R• + X₂ → RX + X•   (X transfer)        BrC-C• + HBr → product + Br•

TERMINATION:                              TERMINATION:
R• + X• → RX                             R• + Br• → RBr
X• + X• → X₂                            Br• + Br• → Br₂

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Similarities Between the Two

Both:
1. Involve free radical intermediates (species with unpaired electrons)
2. Follow 3-stage chain mechanism (Initiation, Propagation, Termination)
3. Initiated by UV light or heat or peroxides
4. Involve homolytic bond cleavage
5. Can be inhibited by radical scavengers (O₂, hydroquinone)
6. Are exothermic chain reactions
7. Produce by-products from termination steps
8. Show no rearrangement (unlike carbocation reactions)

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Key Differences Summary

SUBSTITUTION:
→ Alkane substrate
→ C-H bond breaks
→ H is replaced by X
→ Selectivity governed by C-H bond strength
→ Example: halogenation of methane

ADDITION:
→ Alkene substrate
→ C=C π bond breaks
→ HX adds across double bond
→ Anti-Markovnikov due to radical stability
→ Example: HBr/peroxide on propene

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═══════════════════════════════════════

UNIT 4-6 QUICK REVISION CARD

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╔══════════════════════════════════════════════════════════════════╗
║          ORGANIC CHEMISTRY UNITS 4-6 — QUICK REVISION          ║
╠══════════════════════════════════════════════════════════════════╣
║ UNIT 4 - ELIMINATION                                            ║
║ E1: 2-step, Rate=k[R-X], carbocation, Zaitsev, polar protic    ║
║ E2: 1-step, Rate=k[R-X][Base], anti-periplanar, stereospecific ║
║ High temp → E; High [strong base] → E2; Bulky base → Hofmann  ║
║ Dehydration: ROH + H⁺/heat → alkene (E1 for 3°, E2 for 1°)   ║
╠══════════════════════════════════════════════════════════════════╣
║ UNIT 5 - FREE RADICAL ADDITION                                  ║
║ Markovnikov (no peroxide): H adds to more H-bearing C          ║
║ Anti-Markovnikov (peroxide): Br• adds first → 1-bromoalkane    ║
║ Peroxide effect: ONLY HBr (both prop. steps must be exotherm.) ║
║ Chain: Initiation → Propagation (×10000) → Termination         ║
╠══════════════════════════════════════════════════════════════════╣
║ UNIT 6 - ADVANCED FREE RADICAL                                  ║
║ Allylic halogenation (NBS): substitution at allylic C-H        ║
║ Allylic SN1: delocalized cation → 1,3-rearrangement            ║
║ Conjugated diene: 1,2-addition (kinetic) vs 1,4 (thermodynam.) ║
║ Substitution vs Addition: alkane vs alkene, H-abstraction vs   ║
║ C=C addition, same mechanism but different substrates/products  ║
╚══════════════════════════════════════════════════════════════════╝

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🧪 ORGANIC CHEMISTRY — COMPLETE EXAM ANSWERS

Units 7, 8, 9 & 10 | University Level | 10 Marks Each

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✦ UNIT 7 — AROMATIC CHEMISTRY & EAS

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Q1. Effect of Halogens on Electrophilic Aromatic Substitution in Alkylbenzene (10 Marks)

Introduction to Electrophilic Aromatic Substitution (EAS)

EAS is a reaction in which an electrophile (E⁺) replaces a hydrogen atom on the benzene ring, while the aromatic character of the ring is retained.

General EAS:

      H                   E
      |       E⁺          |
  [benzene]  ────→   [benzene]   +   H⁺

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Substituent Effects in EAS

1. Rate of the next substitution (activating or deactivating)
2. Position of the next substituent (ortho/para directors or meta directors)

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A. Effect of Alkyl Groups (in Alkylbenzene like Toluene)

Toluene (methylbenzene):
         CH₃
          |
        [ring]

Methyl group:
- Donates electrons to ring by +I (inductive) and hyperconjugation
- Increases electron density at ortho and para positions
- ACTIVATES the ring → EAS faster than benzene
- Directs incoming electrophile to ORTHO and PARA positions

Nitration of toluene:
     CH₃                CH₃               CH₃
      |     HNO₃/H₂SO₄   |                  |
   [ring]  ─────────→  [ring]-NO₂  +   [ring]-NO₂  (+small meta)
                       (ortho)           (para) 
                        58%               38%         4%

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B. Effect of Halogens on EAS

┌──────────────────────────────────────────────────────────┐
│ HALOGENS ARE:                                            │
│                                                          │
│  DEACTIVATING (ring is less reactive than benzene)       │
│     AND                                                  │
│  ORTHO/PARA DIRECTING (still direct to o/p positions)    │
│                                                          │
│ This is an UNUSUAL combination:                          │
│ Most activators are o/p directors                        │
│ Most deactivators are meta directors                     │
│ BUT halogens deactivate AND still direct o/p             │
└──────────────────────────────────────────────────────────┘

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Why Halogens DEACTIVATE the Ring

   Cl
    |
 [ring]

Cl is electronegative → pulls electron density from ring
→ ring is electron-poor → electrophile attacks less readily
→ DEACTIVATING effect

Reactivity: Benzene > Chlorobenzene > Dichlorobenzene
            (decreasing reactivity as more Cl added)

---

Why Halogens DIRECT to Ortho/Para

Lone pairs on Cl can donate INTO the ring by resonance:

   :Cl:              :Cl:⁺             :Cl:⁺
    |                  ‖                  ‖
  [ring]   ↔    [ring,δ⁻ ortho] ↔  [ring,δ⁻ para]

→ Electron density increases at ortho and para positions
→ Electrophile attacks ortho and para preferentially
→ ORTHO/PARA director

-I (inductive): removes e⁻ from ring → deactivates
+M (mesomeric/resonance): pushes e⁻ to o/p → directs o/p

Net: DEACTIVATING + ORTHO/PARA DIRECTING

---

Halogen Effect in Alkylbenzene (Combined Effect)

    CH₃
     |          CH₃ = o/p director (activating)
  [ring]        Cl  = o/p director (deactivating)
     |
     Cl

Both direct to ortho/para of their own position
→ Electrophile goes where BOTH direct → reinforced position

   CH₃                    CH₃
    |       HNO₂/H₂SO₄     |
 [ring]    ────────→    [ring]-NO₂
    |                       (position ortho to CH₃ AND para to Cl)
    Cl

• The activating group wins (CH₃ over Cl)
• Electrophile attacks position directed by the stronger activating group

---

Comparison of Directing Effects

┌───────────────┬─────────────────┬────────────────┬──────────────────┐
│ Substituent   │ Effect on ring  │ Direction      │ Example          │
├───────────────┼─────────────────┼────────────────┼──────────────────┤
│ -CH₃, -C₂H₅  │ Activating (+I) │ Ortho/Para     │ Toluene          │
│ -OH, -OR      │ Strongly activ. │ Ortho/Para     │ Phenol           │
│ -NH₂          │ Strongly activ. │ Ortho/Para     │ Aniline          │
│ -F, -Cl, -Br  │ Deactivating-I  │ Ortho/Para     │ Chlorobenzene    │
│               │ but +M          │                │                  │
│ -NO₂, -CN     │ Deactivating    │ Meta           │ Nitrobenzene     │
│ -COOH, -CHO   │ Deactivating    │ Meta           │ Benzoic acid     │
└───────────────┴─────────────────┴────────────────┴──────────────────┘

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Reactivity Order in Halogenated Benzenes

Fluorobenzene > Chlorobenzene > Bromobenzene > Iodobenzene
(+M effect of F strongest → least deactivating overall)

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Q2. Resonance Stabilization of Benzyl Radical (10 Marks)

Introduction

        H
        |
 C₆H₅—CH₂—H  →  C₆H₅—CH₂•  +  H•

           benzyl radical

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Structure of Benzyl Radical

Benzyl radical: C₆H₅—CH₂•

      •CH₂
       |
    [benzene ring]
    
The radical carbon is sp3 hybridized, with the unpaired electron
in a p orbital. This p orbital overlaps with the π system of
the benzene ring → RESONANCE DELOCALIZATION

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Resonance Structures of Benzyl Radical

Structure 1:       Structure 2:       Structure 3:       Structure 4:
                                                          
   •CH₂               CH₂                CH₂                CH₂
    |                  ‖                   |                   ‖
 [benzene]    ↔    [ring,• ortho] ↔   [ring,• para] ↔  [ring,• ortho']

More precisely:

  •CH₂—           •             •             •
   |          CH₂—(ring  ↔  ring)    and other
  [ o p m ]       resonance structures

   CH₂•               CH₂                CH₂                CH₂
    |                   |                   |                   |
  ⬡         ↔       ⬡·           ↔     ⬡·           ↔    ⬡·
             (ortho)              (para)             (ortho')

The • is delocalized over 4 positions:
  - exocyclic CH₂
  - ortho carbon
  - para carbon
  - other ortho carbon

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Why Benzyl Radical is Exceptionally Stable

DELOCALIZATION = STABILITY

1. Normal secondary radical: radical on ONE carbon only → less stable

2. Benzyl radical: radical delocalized over 4 positions (ring + CH₂)
   → energy is spread over many atoms
   → much more stable

Stability: Benzyl > Allylic > Tertiary > Secondary > Primary

Benzyl radical is the MOST STABLE carbon radical.

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Evidence for Stability

Bond         BDE (kcal/mol)    Interpretation
─────────────────────────────────────────────────
CH₃-H           104            Methyl - least stable radical
1° C-H          100            Primary radical
2° C-H           96            Secondary radical
3° C-H           91            Tertiary radical
Allylic C-H      88            Allylic radical (resonance stab.)
Benzylic C-H     85            BENZYL radical (most stable)

Lower BDE → Weaker bond → More stable radical formed
Benzyl C-H is the WEAKEST → Benzyl radical is MOST STABLE

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Practical Consequence: Selectivity in Free Radical Reactions

Toluene + Cl₂ + hν:

    CH₃                CH₂Cl
     |       Cl•         |
  [ring]   ──────→   [ring]   +  HCl
  
Cl• abstracts benzylic H (weakest) → benzyl radical
Benzyl radical + Cl₂ → benzyl chloride + Cl•

Product: Benzyl chloride (C₆H₅CH₂Cl)
NOT ring chlorination (ionic mechanism needed for that)

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NBS (N-Bromosuccinimide) Bromination at Benzylic Position

C₆H₅—CH₃  +  NBS  ──hν──→  C₆H₅—CH₂Br  +  Succinimide

Benzyl bromide formed selectively at benzylic position
(NBS provides low concentration of Br₂ → only weakest C-H attacked)

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Benzyl Cation and Benzyl Anion - Also Resonance Stabilized

Benzyl cation (C₆H₅CH₂⁺): + charge delocalized → very stable → SN1 very easy
Benzyl anion (C₆H₅CH₂⁻): - charge delocalized → fairly acidic CH
Benzyl radical (C₆H₅CH₂•): radical delocalized → most stable radical

All three are stabilized by the same resonance mechanism.

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Q3. Free Radical Friedel-Crafts Alkylation with Mechanism (10 Marks)

Introduction

1. Ionic (electrophilic) - Classical Friedel-Crafts, uses Lewis acid catalyst (AlCl₃)
2. Free Radical - Occurs under radical conditions (no Lewis acid)

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Classical Friedel-Crafts Alkylation (Brief - for context)

[Benzene] + R-Cl ──[AlCl₃]──→ [Benzene-R] + HCl
(EAS mechanism - ionic - carbocation electrophile attacks ring)

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Free Radical Friedel-Crafts Alkylation

[Benzene] + R• ──→ [Benzene-R] + H•   (radical mechanism)

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Reagents for Free Radical Alkylation:

• Alkyl halides (RX) + UV light
• Peroxides (RO-OR) → generate alkyl radicals
• Di-tert-butyl peroxide: (CH₃)₃CO—OC(CH₃)₃ → 2(CH₃)₃CO• → •CH₃ + acetone

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Mechanism of Free Radical Alkylation

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(CH₃)₃C—O—O—C(CH₃)₃  ──hν/Δ──→  2 (CH₃)₃C—O•
(di-tert-butyl peroxide)             (tert-butoxy radical)

(CH₃)₃C—O•  →  •C(CH₃)₃  +  [O=CH₂... but actually acetone]

More correctly:
(CH₃)₃CO•  →  CH₃• + (CH₃)₂C=O  (β-scission → methyl radical)

         •
         |
  R•  +  [benzene]  →  R—[ring with unpaired e⁻]
                         (cyclohexadienyl radical = Wheland intermediate radical)

       R
       |
CH₃• + C₆H₆ → [  cyclohexadienyl radical  ]
                  (spin density on ring carbons)
                  
       R
      /
[ring]•   ← radical intermediate (cyclohexadienyl radical)

     R                  R
     |                  |
  [ring•]  →        [ring]   +   H•
  
(radical loses H to restore aromaticity)

R• + R• → R-R
R• + H• → R-H
cyclohexadienyl radical + R• → alkylated product

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Complete Mechanism Summary (Diagram)

INITIATION:
ROOR ──hν──→ 2RO• ──→ 2R• (or R• + acetone)

PROPAGATION CYCLE:
         R•
          ↓ (adds to ring)
    [cyclohexadienyl radical]
          ↓ (-H•)
    [alkylated benzene] + H•
    
    H• + RH → R• + H₂  (new radical to continue chain)

TERMINATION:
    R• + R• → R₂ (no more chain)

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Product Orientation in Free Radical Alkylation

Free radical attacks all ring positions with less preference:
→ Mixture of ortho, meta, and para products
→ Statistical ratio approximately 2 ortho : 1 meta : 1 para (with some preference)
→ No rearrangement (unlike ionic Friedel-Crafts where carbocation can rearrange)

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Comparison: Ionic vs Free Radical Friedel-Crafts

┌──────────────────────┬──────────────────────┬──────────────────────┐
│ Feature              │ Ionic (Classical)    │ Free Radical         │
├──────────────────────┼──────────────────────┼──────────────────────┤
│ Catalyst             │ Lewis acid (AlCl₃)   │ hν or peroxide       │
│ Intermediate         │ Carbocation (R⁺)     │ Carbon radical (R•)  │
│ Mechanism            │ EAS (electrophilic)  │ Radical chain        │
│ Selectivity          │ Good (o/p or m)      │ Poor (statistical)   │
│ Rearrangement        │ Yes (via carbocation)│ No                   │
│ Conditions           │ Anhydrous, Lewis acid│ UV light, heat       │
└──────────────────────┴──────────────────────┴──────────────────────┘

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Q4. Determination, Orientation and Relative Reactivity of EAS (10 Marks)

What is EAS (Electrophilic Aromatic Substitution)?

EAS is the replacement of an aromatic ring hydrogen by an electrophile, retaining the aromatic character of the ring.

      H                  E
      |       E⁺/catalyst  |
   [benzene] ──────────→  [benzene]  +  H⁺

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General Mechanism of EAS

         H  E                    H  E
          \ /                     \ /
    E⁺ +  C    →    [  carbocation  ]
         /\                     /\
        (ring)                (ring - partial positive charge)
        
        Arenium ion (Wheland intermediate) - sp3 carbon at attack site
        - Cationic, not aromatic (ring interrupted)
        - SLOW step (rate-determining)

    H  E                    E
     \ /      -H⁺           |
   [arenium]  ────→      [aromatic ring]  +  H⁺
   
   Fast step - restores aromatic stability

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Determination of Directing Effect

For ACTIVATING GROUPS (e.g., -NH₂, -OH, -CH₃):

    Attack at PARA position:
    NH₂                NH₂⁺
     |    E⁺ at para     |
  [ring]  ──────────→  [ring with + charge distributed]
                       + charge lands on NITROGEN in one resonance structure
                       → very stable (nitrogen stabilizes +)
                       → FAVORABLE

    Attack at META:
    + charge NEVER on nitrogen → less stable → less favorable

    → So: NH₂ directs ortho/para (+ charge in resonance lands on nitrogen)

For DEACTIVATING GROUPS (e.g., -NO₂):

    Attack at ORTHO/PARA:
    NO₂                NO₂
     |   E⁺ at para     |
  [ring] ──────→  [ring with + charge on NO₂ carbon = very unstable]
                    → UNFAVORABLE

    Attack at META:
    + charge stays AWAY from NO₂ group → less destabilization
    → META attack preferred

    → So: NO₂ directs meta

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Orientation Summary

ORTHO/PARA DIRECTORS (activating):
  -NH₂, -NHR, -NR₂    (strongest activators)
  -OH, -OR             (strong activators)
  -CH₃, alkyl          (weak activators, via hyperconjugation)
  -NHCOR, -OCOR        (moderate activators)

ORTHO/PARA DIRECTORS (deactivating - halogens):
  -F, -Cl, -Br, -I    (deactivating by -I, but o/p by +M)

META DIRECTORS (deactivating):
  -NO₂, -N⁺R₃          (strong deactivators)
  -CN, -COOH, -COOR    (moderate deactivators)
  -CHO, -COR           (moderate deactivators)
  -SO₃H                (deactivator)

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Relative Reactivity

Reactivity order:
N(CH₃)₂ > NH₂ > OH > OCH₃ > NHCOR > CH₃ > H (benzene) > Cl > Br > NO₂

Most reactive ─────────────────────────────────→ Least reactive

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The ESR (Electron Spin Resonance) Connection

ESR measures: unpaired electron behavior in radical species
Application to aromatic EAS:
→ Studies cyclohexadienyl radical
→ Confirms spin density at ortho and para positions
→ Supports o/p directing mechanism

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How to Predict Orientation (Step-by-Step)

Step 1: Identify the substituent already on the ring
Step 2: Classify it as o/p director or meta director
Step 3: If o/p director → draw o/p positions relative to it
Step 4: If meta director → draw meta positions
Step 5: If TWO groups: 
    - Identify activating group → it dominates
    - If same type: use reinforced position (where both direct)
    - If opposing: activating group wins

Step 6: Draw the major product

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Summary Diagram

             Substituent on benzene ring
                         |
            ┌────────────┴───────────────┐
            │                            │
    Electron-donating               Electron-withdrawing
    (+I and/or +M)                  (-I and/or -M)
            │                            │
     ACTIVATES RING               DEACTIVATES RING
            │                            │
   ┌────────┴──────┐              ┌──────┴──────────┐
   │               │              │                  │
 Strong         Weak           Halogens           Strong EWG
 (NH₂, OH)     (alkyl)        (-I+M both)        (NO₂, CN, COOH)
   │               │              │                  │
o/p director   o/p director   o/p director      META director

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═══════════════════════════════════════

✦ UNIT 8 — CONDENSATION REACTIONS

═══════════════════════════════════════

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Q1. Cross Aldol Condensation with Mechanism (10 Marks)

What is Aldol Condensation?

Aldol condensation is a reaction between two carbonyl compounds (aldehydes or ketones) in the presence of a dilute base or acid, where one acts as an enol/enolate (nucleophile) and the other as an electrophilic carbonyl (electrophile), forming a β-hydroxy carbonyl compound (aldol), which then dehydrates to form an α,β-unsaturated carbonyl compound.

---

Simple vs Cross Aldol Condensation

SIMPLE ALDOL: Two molecules of the SAME compound react
Example: 2 CH₃CHO → CH₃CH(OH)CH₂CHO (acetaldol)

CROSS ALDOL: Two DIFFERENT carbonyl compounds react
Example: CH₃CHO + HCHO → HOCH₂CH₂CHO (using excess HCHO)

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Cross Aldol Condensation

Cross aldol works CLEANLY when:
One compound has NO α-hydrogen → cannot form enolate
→ Acts only as electrophile (acceptor)

Compounds with no α-H:
- Formaldehyde (HCHO)
- Benzaldehyde (C₆H₅CHO)
- Trimethylacetaldehyde [(CH₃)₃CCHO]
- Ketones with no α-H on one side

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Mechanism of Cross Aldol Condensation

---

           H      O                     O
           |      ‖       NaOH           ‖
    CH₃—C—H  +  OH⁻  ────────→   CH₂=C—H    (enolate anion)
    (α-H removed)                  ⁻
    
    acetaldehyde → acetaldehyde enolate

      O⁻                O                O  OH
      ‖                 ‖                ‖   |
 CH₂=C—H  +  C₆H₅—C—H  →  C₆H₅—CH—CH₂—C—H
 (enolate)   (benzaldehyde)           
                                (aldol product - β-hydroxy aldehyde)

      O   OH
      ‖   |
C₆H₅—CH—CH₂—CHO  +  H₂O
(3-hydroxy-3-phenylpropanal = β-hydroxy aldehyde)

      OH                               
      |       heat/-H₂O                
C₆H₅—CH—CH₂—CHO  ──────────→  C₆H₅—CH=CH—CHO   +  H₂O
                                (Cinnamaldehyde)
                                (trans, conjugated - more stable)

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Overall Reaction Summary

C₆H₅CHO  +  CH₃CHO  ──[NaOH]──→  C₆H₅—CH=CH—CHO  +  H₂O
(benzaldehyde)  (acetaldehyde)      (cinnamaldehyde)

C₆H₅CHO has NO α-H → acts ONLY as electrophile
CH₃CHO has α-H → forms enolate → acts as nucleophile
→ Clean cross aldol (no self-condensation of benzaldehyde)

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Other Important Cross Aldol Examples

C₆H₅CHO  +  CH₃COCH₃  ──[NaOH]──→  C₆H₅CH=CHCOCH₃  +  H₂O
(benzaldehyde) (acetone)               (chalcone)

R-CO-CH₃  +  HCHO  +  R₂NH  ──→  Mannich base (β-amino carbonyl)

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Energy Profile of Aldol

Energy
  ^        ‡ (TS for C-C bond formation)
  |        /\
  |       /  \   aldol
  |      /    \  product
  |─────/      \──────────────────
  Reactants                   Products

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Q2. Mechanism of Perkin Condensation (10 Marks)

Introduction

Perkin Condensation (William Henry Perkin, 1868) is the condensation of an aromatic aldehyde with an acid anhydride in the presence of the sodium/potassium salt of the corresponding acid, to give an α,β-unsaturated carboxylic acid (cinnamic acid and its derivatives).

---

General Reaction

ArCHO  +  (RCH₂CO)₂O  ──[RCH₂COONa, heat]──→  ArCH=CR-COOH  +  RCH₂COOH

Aromatic   Acid anhydride    Salt of acid           α,β-unsaturated
aldehyde                     (base catalyst)          carboxylic acid

C₆H₅CHO  +  (CH₃CO)₂O  ──[CH₃COONa, heat]──→  C₆H₅CH=CH-COOH  +  CH₃COOH
(benzaldehyde) (acetic anhydride)  (sodium acetate)   (cinnamic acid)

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Mechanism of Perkin Condensation

         O    O                        O    O
         ‖    ‖    CH₃COO⁻             ‖    ‖
 CH₃—C—O—C—CH₃   ──────────→   ⁻CH₂—C—O—C—CH₃
 (acetic anhydride)              (active methylene carbanion)
 
Na acetate acts as BASE: removes α-H from CH₃CO— of anhydride

     O    O
     ‖    ‖                      OH
  ⁻CH₂—C—O—C—CH₃  +  C₆H₅—CHO  →  C₆H₅—CH—CH₂—CO—O—COCH₃
  (carbanion)      (benzaldehyde)     
                                  (tetrahedral intermediate - β-alkoxide)

      OH
      |
C₆H₅—CH—CH₂—CO—O—CO—CH₃
      
Internal proton transfer or deprotonation:

→   O⁻
    |
C₆H₅—CH—CH₂—CO—O—CO—CH₃
(alkoxide intermediate)

C₆H₅—CH(O⁻)—CH₂—CO—O—CO—CH₃

→  The carboxyl oxygen attacks the carbonyl of the second acetyl group
→  Mixed anhydride-like intermediate forms
→  Loss of acetate

      O⁻                        
      |    
C₆H₅—CH—CH₂—CO—O—COCH₃   →  C₆H₅—CH=CH—CO—O—COCH₃  +  OH⁻
                              (α,β-unsaturated mixed anhydride)

C₆H₅—CH=CH—CO—O—COCH₃  +  H₂O  →  C₆H₅—CH=CH—COOH  +  CH₃COOH
                                     (cinnamic acid - PRODUCT)

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Summary Reaction

INPUT:  C₆H₅CHO + (CH₃CO)₂O + CH₃COONa (heat, 180°C)

OUTPUT: C₆H₅CH=CH-COOH (trans-cinnamic acid) + CH₃COOH

CONDITIONS: High temperature (150-200°C)
            Sodium or potassium salt of the acid

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Key Points about Perkin Condensation

1. Only AROMATIC ALDEHYDES react (aliphatic aldehydes are too reactive - undergo self-condensation)
2. The carboxylate salt MUST correspond to the anhydride used
3. Product is always trans (E) - cinnamaldehyde-like compound
4. No α-H on aromatic aldehyde → clean reaction with no self-condensation
5. The mechanism is essentially: base-catalyzed aldol-type condensation

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Applications of Perkin Condensation

→ Synthesis of cinnamic acid (from benzaldehyde + acetic anhydride)
→ Synthesis of coumarin (from salicylaldehyde + acetic anhydride)
→ Synthesis of α,β-unsaturated amino acids (modified Perkin)

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Q3. Mechanism of Cannizzaro Reaction (10 Marks)

Introduction

Cannizzaro Reaction (Stanislao Cannizzaro, 1853) is a disproportionation reaction of an aldehyde that has NO α-hydrogen, in the presence of concentrated NaOH, where one molecule is oxidized to a carboxylic acid (salt) and another is reduced to an alcohol.

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Key Requirement

The aldehyde must have NO α-hydrogen (no H on C adjacent to CHO).

Why? Aldehydes WITH α-H undergo aldol condensation instead.

Aldehydes that undergo Cannizzaro:
- Formaldehyde (HCHO)
- Benzaldehyde (C₆H₅CHO)
- Trimethylacetaldehyde [(CH₃)₃CCHO]
- 2,2-Dimethylpropanal
- Furfural (furan-2-carboxaldehyde)

---

General Reaction

2 RCHO  ──[conc. NaOH]──→  RCOO⁻Na⁺  +  RCH₂OH
(2 molecules of aldehyde)   (carboxylate salt)  (alcohol)

One molecule is OXIDIZED (aldehyde → acid)
One molecule is REDUCED (aldehyde → alcohol)

2 HCHO  ──[conc. NaOH]──→  HCOONa  +  CH₃OH
(formaldehyde)              (sodium formate)  (methanol)

2 C₆H₅CHO  ──[conc. NaOH]──→  C₆H₅COONa  +  C₆H₅CH₂OH
(benzaldehyde)                 (sodium benzoate)  (benzyl alcohol)

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Mechanism of Cannizzaro Reaction

         O                        O⁻
         ‖        OH⁻              |
  C₆H₅—C—H  ─────────→  C₆H₅—C—H
                                   |
                                   OH
                           (tetrahedral alkoxide)

The tetrahedral intermediate (with OH and O⁻) is now a hydride donor.

        O⁻                          O
        |                           ‖
C₆H₅—C—H   +   C₆H₅—CHO  →   C₆H₅—C—O⁻  +  C₆H₅—CH₂—O⁻
        |        (second molecule)  (benzoate)    (benzyl alkoxide)
        OH

  The H (as H⁻ hydride) migrates from the first aldehyde to the C=O of the second aldehyde.
  This is a NUCLEOPHILIC HYDRIDE TRANSFER (not a proton - it is hydride H⁻).

C₆H₅—CH₂—O⁻  +  H₂O  →  C₆H₅—CH₂—OH  +  OH⁻
(benzyl alkoxide)           (benzyl alcohol)

The carboxylate (C₆H₅COO⁻) remains as sodium benzoate salt.

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Complete Mechanism Diagram

STEP 1:
  C₆H₅CHO  +  OH⁻  →  C₆H₅CH(OH)(O⁻)     [OH adds to carbonyl]

STEP 2 (RATE-DETERMINING STEP):
                                O⁻
                                |
  C₆H₅CHO  +  C₆H₅—C—H   →  C₆H₅—COO⁻  +  C₆H₅—CH₂O⁻
              (H⁻ transfer  from activated aldehyde to second aldehyde)
                 OH
              (hydride donor)   (oxidized)      (reduced)

STEP 3:
  C₆H₅CH₂O⁻  +  H₂O  →  C₆H₅CH₂OH  +  OH⁻

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Cross-Cannizzaro Reaction

Formaldehyde is most reactive → preferentially reduced to methanol:

HCHO  +  C₆H₅CHO  ──[NaOH]──→  CH₃OH  +  C₆H₅COONa
(HCHO reduced to MeOH)  (benzaldehyde oxidized to benzoate)

This is the Tischenko reaction variant / Cross Cannizzaro.

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Important Features of Cannizzaro Reaction

✓ No α-hydrogen required (distinguishes from aldol condensation)
✓ Concentrated NaOH (dilute NaOH gives aldol if α-H present)
✓ Involves hydride (H⁻) transfer - NOT proton (H⁺) transfer
✓ Disproportionation: one oxidized, one reduced
✓ 1:1 ratio of acid salt to alcohol obtained
✓ Formaldehyde most reactive in cross-Cannizzaro
✓ Mechanism: nucleophilic addition of OH⁻ → hydride transfer (RDS) → products

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═══════════════════════════════════════

✦ UNIT 9 — NAMED ORGANIC REACTIONS

═══════════════════════════════════════

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Q1. Williamson Synthesis (10 Marks)

Introduction

Williamson Synthesis (Alexander Williamson, 1852) is the most important and direct method for the synthesis of ethers (both symmetrical and unsymmetrical) by the reaction of an alkoxide ion with an alkyl halide (or other alkylating agent) via an SN2 mechanism.

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General Reaction

R—O⁻  +  R'—X  ──SN2──→  R—O—R'   +   X⁻
(alkoxide)  (alkyl halide)   (ether)   (halide ion)

CH₃O⁻  +  C₂H₅Br  ──→  CH₃—O—C₂H₅  +  Br⁻
(methoxide)  (ethyl bromide)  (methyl ethyl ether)

---

Preparation of Alkoxide (First Step)

R—OH  +  Na (or K)  ─────→  R—O⁻Na⁺  +  ½H₂
(alcohol)  (sodium metal)     (sodium alkoxide)    (hydrogen gas)

Or: R-OH + NaH → R-O⁻Na⁺ + H₂ (sodium hydride)
Or: R-OH + NaNH₂ → R-O⁻Na⁺ + NH₃

---

Mechanism of Williamson Synthesis (SN2)

C₂H₅—OH  +  Na  →  C₂H₅—O⁻Na⁺  +  ½H₂
(ethanol)             (sodium ethoxide)

SN2 step:

         δ-     δ-
  EtO⁻ + CH₂—Br   →   [EtO---CH₂---Br]‡   →  EtO-CH₂-Et  +  Br⁻
           CH₃              (transition state)    (diethyl ether)

---

Types of Ethers Synthesized

2 R—OH  ──[Na, then self-alkylate]──→  R—O—R  (symmetric)

Or: CH₃OH + Na → CH₃O⁻Na⁺ + ½H₂
    CH₃O⁻Na⁺ + CH₃I → CH₃OCH₃ + NaI
    (Dimethyl ether)

CH₃O⁻Na⁺  +  C₂H₅Br  →  CH₃OC₂H₅  +  NaBr
(methoxide)   (ethyl bromide)  (methyl ethyl ether)

Key: Alkoxide from one alcohol, alkyl halide from another

C₆H₅—OH  +  NaOH  →  C₆H₅—O⁻Na⁺   (sodium phenoxide)
C₆H₅—O⁻Na⁺  +  CH₃I  →  C₆H₅—O—CH₃  +  NaI
                            (anisole / methyl phenyl ether)

---

Rules for Choosing Reagents (Important!)

BEST: R-O⁻ + 1° R'-X → good SN2 yield
OK:   R-O⁻ + 2° R'-X → slower SN2 (some E2)
BAD:  R-O⁻ + 3° R'-X → ONLY E2 (elimination!) - NO SN2

So: For unsymmetrical ether, put the bulkier group as the ALKOXIDE,
    and use a PRIMARY alkyl halide for the SN2 step.

Example: To make tert-butyl methyl ether:

WRONG approach: tert-BuO⁻ + CH₃Br → (t-Bu-O-CH₃) ← this works since CH₃Br is primary ✓
WRONG approach: CH₃O⁻ + tert-BuBr → only elimination (E2) ✗

CORRECT: (CH₃)₃C—O⁻  +  CH₃—Br  →  (CH₃)₃C—O—CH₃  ✓

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Applications of Williamson Synthesis

1. Synthesis of simple dialkyl ethers
2. Synthesis of aryl ethers (phenol + alkyl halide)
3. Synthesis of cyclic ethers (intramolecular Williamson)
4. Important in drug synthesis (many drugs contain ether linkages)
5. Synthesis of methyl ethers for protection of OH groups

BrCH₂CH₂OH + NaOH → BrCH₂CH₂O⁻Na⁺ 
→ intramolecular SN2 → Ethylene oxide (3-membered ring)

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Q2. Fries Rearrangement (10 Marks)

Introduction

Fries Rearrangement (Karl Fries, 1908) is the conversion of a phenyl ester (aryl ester) into a hydroxy aryl ketone (either ortho or para isomer) upon treatment with a Lewis acid catalyst (usually AlCl₃) and heat.

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General Reaction

     O—CO—R                      OH                  OH
      |          AlCl₃            |                    |
   [ring]   ──────────→      [ring]-CO-R    +    [ring]
      (ester on ring)         (o-hydroxy         (p-hydroxy
       (phenyl ester)          ketone)            ketone)

         O—COCH₃                    OH                  OH
          |          AlCl₃           |                    |
     [C₆H₄]   ──────────────→  [C₆H₄]-COCH₃   +   [C₆H₄]-COCH₃
    (phenyl acetate)              (o-hydroxy         (p-hydroxy
                                  acetophenone)       acetophenone)

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Mechanism of Fries Rearrangement

     O—CO—R                    O   O—AlCl₃
      |          AlCl₃          |   |
   [ring]   ────────────→   [ring]  +  [R—C≡O]⁺
                              (phenol with O-AlCl₃)  (acylium ion)
                              
OR: AlCl₃ breaks C-O bond of ester → phenolate anion + acylium ion pair

     [phenolate-AlCl₃]  +  [RCO⁺]
              ↓
     EAS: acylium attacks ORTHO or PARA position of ring

        OH                       OH
         |        RCO⁺            |
      [ring]   ──────────→    [ring]-COR   (electrophilic attack)
                                (at o or p position)

     OH              OH
      |                |
   [ring]-CO-R → [ring]-CO-R  +  H⁺
    H  (arenium)     (hydroxy ketone - final product)

---

Temperature Effect on Fries Rearrangement

┌──────────────────────┬───────────────────────────────────────────┐
│ Temperature          │ Major Product                             │
├──────────────────────┼───────────────────────────────────────────┤
│ LOW temperature      │ PARA isomer (p-hydroxy aryl ketone)       │
│ (0-25°C)             │ (thermodynamic product - more stable)     │
├──────────────────────┼───────────────────────────────────────────┤
│ HIGH temperature     │ ORTHO isomer (o-hydroxy aryl ketone)      │
│ (>100°C)             │ (kinetic product - via intramolecular TS) │
└──────────────────────┴───────────────────────────────────────────┘

---

Photo-Fries Rearrangement

Phenyl esters can ALSO rearrange when exposed to UV light 
(no AlCl₃ needed):
→ Photo-Fries Rearrangement
→ Also gives o- and p-hydroxy ketones
→ Proceeds via radical or excited-state mechanism

---

Applications of Fries Rearrangement

1. Synthesis of hydroxy ketones (important intermediates)
2. Synthesis of o-hydroxyacetophenone → used in dye synthesis
3. Synthesis of natural products and pharmaceuticals
4. Synthesis of 2-hydroxyacetophenone → preparation of chromone derivatives
5. Route to flavonoids and coumarin derivatives

---

Q3. Kolbe Reaction (Kolbe-Schmitt Reaction) (10 Marks)

Introduction

Kolbe Reaction (Kolbe-Schmitt Reaction; Adolph Kolbe 1860, modified by Schmitt 1885) is the carboxylation of sodium or potassium phenoxide with CO₂ under high pressure and temperature to give a hydroxy aromatic carboxylic acid (primarily salicylic acid from sodium phenoxide).

---

General Reaction

         ONa                    OH
          |       CO₂            |
       [ring]  ──────────→   [ring]—COOH
              (125-150°C,
               4-7 atm)
               
Sodium phenoxide + CO₂ → Salicylic acid (2-hydroxybenzoic acid)

C₆H₅—ONa  +  CO₂  ──[125°C, 4-7 atm]──→  HOC₆H₄—COONa  ──[H⁺]──→  HOC₆H₄—COOH
(sodium phenoxide)                          (sodium salicylate)       (salicylic acid)

---

Mechanism of Kolbe Reaction

         O⁻Na⁺                 O—CO₂Na⁺
          |       CO₂            |
       [ring]  ──────────→   [ring]   (CO₂ inserts into O-ring bond at ortho C)

     O⁻                     O—CO₂⁻
      |         +CO₂          |
   [ring]  ──────────→   [ring]
   (nucleophile)           (carboxylate formed at oxygen)

     O—COO⁻                OH
      |           →          |
   [ring]              [ring]—COO⁻  (carboxyl group now on ring C at ortho position)
   
   The C=O of CO₂ was originally O-carboxylated
   Then rearranges → C-carboxylated product (more stable)

   OH                   OH
    |       H⁺/H₂O       |
[ring]—COO⁻  ────────→  [ring]—COOH
(sodium salicylate)      (salicylic acid)

---

Ortho vs Para Product (Na vs K salt)

┌──────────────────────┬─────────────────────────────────────────────┐
│ Metal Cation         │ Major Product                               │
├──────────────────────┼─────────────────────────────────────────────┤
│ Sodium (Na⁺)         │ ORTHO product (salicylic acid) ← MAJOR      │
│ (small cation)       │ (ortho position closer to ONa⁺ via chelation)│
├──────────────────────┼─────────────────────────────────────────────┤
│ Potassium (K⁺)       │ PARA product (p-hydroxybenzoic acid) ← MAJOR│
│ (larger cation)      │ (larger K can direct to para)               │
└──────────────────────┴─────────────────────────────────────────────┘

---

Applications of Kolbe Reaction

1. Industrial synthesis of SALICYLIC ACID (major application)
2. Salicylic acid → Aspirin (acetylsalicylic acid) → most important use
3. Synthesis of p-hydroxybenzoic acid (used as preservative - parabens)
4. Synthesis of various hydroxy acids for pharmaceutical use

---

Kolbe Electrolysis (Different from Kolbe-Schmitt)

Note: There is also "Kolbe Electrolysis" (different reaction):
Carboxylic acid + electrolysis → R-R (coupling of alkyl groups) + CO₂
This is different from Kolbe-Schmitt reaction.

---

Q4. Reimer-Tiemann Reaction (10 Marks)

Introduction

Reimer-Tiemann Reaction (Karl Reimer and Ferdinand Tiemann, 1876) is the formylation of phenol (introduction of a -CHO group) using chloroform (CHCl₃) and concentrated NaOH to give ortho-hydroxybenzaldehyde (salicylaldehyde) as the major product, with para isomer as minor product.

---

General Reaction

     OH                           OH                    OH
      |     CHCl₃/NaOH             |                     |
   [ring]  ──────────────→     [ring]—CHO    +       [ring]
           (60-70°C)             (ortho)               (para)
                            (salicylaldehyde)      (p-hydroxybenz-
                             MAJOR - 30-35%          aldehyde)
                                                     MINOR

---

Mechanism of Reimer-Tiemann Reaction

CHCl₃  +  NaOH  →  :CCl₂  +  NaCl  +  H₂O
(chloroform)         (dichlorocarbene - electrophilic carbene!)

Mechanism of carbene formation:
CHCl₃  +  OH⁻  →  CCl₃⁻  +  H₂O    (deprotonation at α-C)
CCl₃⁻          →  :CCl₂  +  Cl⁻    (loss of chloride → carbene)

C₆H₅—OH  +  NaOH  →  C₆H₅—O⁻Na⁺  +  H₂O
(phenol)               (sodium phenoxide)

         O⁻                     O⁻
          |       :CCl₂           |         CCl₂H
       [ring]   ────────→     [ring] ← 
                              (ortho attack by carbene)
                              
         O⁻
          |
       [ring]—CHCl₂   (after carbene inserts and H shift)
             (ortho)

     O⁻                    O⁻
      |     :CCl₂           |
  [ring]  ────────→     [ring]
                        ortho C now has —CCl₂⁻ group

     O⁻
      |
  [ring]—CHCl₂    (dichloro intermediate at ortho position)

      O⁻                    OH
       |       H₂O/NaOH      |
   [ring]—CHCl₂  ────────→  [ring]—CHO   +   2 Cl⁻
                              (salicylaldehyde)

-CHCl₂ → -CH(OH)₂ (geminal diol) → -CHO (aldehyde)

---

Complete Mechanism Flowchart

CHCl₃ + NaOH → :CCl₂ + NaCl + H₂O     [CARBENE FORMATION]
                ↓
C₆H₅OH + NaOH → C₆H₅O⁻Na⁺             [PHENOXIDE FORMATION]
                ↓
:CCl₂ attacks ortho-C of phenoxide      [EAS by CARBENE]
                ↓
Intermediate: C₆H₄(O⁻)(ortho-CHCl₂)   [DICHLOROMETHYL GROUP]
                ↓
NaOH/H₂O hydrolyzes -CHCl₂ → -CHO     [HYDROLYSIS]
                ↓
2-Hydroxybenzaldehyde (SALICYLALDEHYDE) [PRODUCT]

---

Why Ortho Major?

The phenoxide anion has O⁻ which:
1. Activates the ring strongly
2. The bulky :CCl₂ carbene prefers ortho attack (directed by O⁻)
3. Ortho attack forms a more stable intermediate (6-membered chelate 
   with Na⁺ coordinating O⁻ and carbene)
4. Para product also forms but as minor product

---

Abnormal Reimer-Tiemann Reaction

When PHENOL IS USED with ortho and para positions BLOCKED:
→ "Abnormal Reimer-Tiemann" product forms
→ Dichlorocarbene inserts into the ring
→ Cyclohexadienone (ring expansion) product formed

Example: 2,6-blocked phenol → :CCl₂ attacks only C-1 → ring expansion → 
forms CYCLOPENTADIENYL carbaldehyde

---

Applications

1. Synthesis of salicylaldehyde (used in perfumery, dyes)
2. Synthesis of 3-formyl-2-hydroxy thiophene analogs
3. Preparation of ortho-hydroxy aromatic aldehydes in general
4. Academic importance: classic demonstration of carbene chemistry

---

═══════════════════════════════════════

✦ UNIT 10 — PHARMACEUTICAL PREPARATIONS

═══════════════════════════════════════

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Q1. Urea — Preparation, Purity Test and Medicinal Uses (10 Marks)

Introduction to Urea

Urea (carbamide) is an organic compound with formula NH₂—CO—NH₂ (or CO(NH₂)₂). It is the end product of protein metabolism in mammals and the first organic compound synthesized in the laboratory (Wohler, 1828).

Structure:
        O
        ‖
  H₂N—C—NH₂
  (urea - diamide of carbonic acid)

Molecular formula: CH₄N₂O
Molecular weight: 60.06 g/mol
Appearance: White, crystalline solid
Melting point: 132-135°C
Solubility: Very soluble in water

---

Preparation of Urea

STEP 1: Formation of ammonium carbamate
NH₃ + CO₂ → NH₂COONH₄    (at 150-200°C, 150-300 atm)
(ammonia)    (ammonium carbamate)

STEP 2: Dehydration of ammonium carbamate → Urea
NH₂COONH₄  ──[heat]──→  NH₂CONH₂  +  H₂O
(ammonium carbamate)       (urea)

AgNCO  +  NH₄Cl  →  NH₄NCO  →  NH₂CONH₂
(silver cyanate) (ammonium chloride)  (ammonium cyanate) (urea - heat rearrangement)

Historical significance: First proof that organic compounds can be made from inorganic materials.

COCl₂  +  2NH₃  →  NH₂CONH₂  +  2HCl
(phosgene)            (urea)

(NH₄)₂CO₃  ──[heat]──→  NH₂CONH₂  +  H₂O  +  CO₂

---

Purity Tests for Urea (IP/BP Tests)

Pure urea: MP = 132-135°C (official range)
Impure: lower or broader melting range
Test: Capillary tube method

Urea + Xanthydrol (C₁₃H₁₀O₂) in glacial acetic acid
→ Forms DIXANTHYL UREA (white precipitate)

   2 Xanthydrol + H₂N—CO—NH₂ → Dixanthyl urea (white ppt.) + 2H₂O

This is SPECIFIC for urea (biuret does not give this)
MP of dixanthyl urea: 269-270°C

Urea + NaOH + CuSO₄ → No biuret color with urea alone
BUT urea on heating → biuret: NH₂CONHCONH₂
Biuret + CuSO₄/NaOH → PURPLE COLOR (biuret reaction)

Note: Pure urea at room temp does NOT give biuret color.
Heating urea gives biuret → then gives purple color.

Heat at 80°C for 2 hours
Allowed weight loss: NMT 1.0%
(urea should not be hygroscopic; excess loss indicates moisture)

Urea: 46.7% nitrogen (theoretical: 2×14/60 × 100)
IP specification: 46.3-46.6% nitrogen
Method: Kjeldahl digestion → distillation → titration

Lead (Pb) limit: NMT 10 ppm
Arsenic limit: NMT 2 ppm
(Test by standard colorimetric/atomic absorption methods)

Dissolve in water:
+ BaCl₂ → no white ppt (sulfate absent)
+ AgNO₃ → no white ppt (chloride absent)

---

Medicinal Uses of Urea

1. DIURETIC: Osmotic diuretic - reduces intracranial and intraocular pressure
   Dose: 1-1.5 g/kg IV as 30% solution in 10% D5W
   Use: Cerebral edema, acute glaucoma

2. KERATOLYTIC (Topical): Urea cream 10-40%
   Softens and removes thickened/hardened skin (hyperkeratosis)
   Used in: Psoriasis, eczema, ichthyosis, dry cracked heels
   Brand: Calmurid, Uremol

3. WOUND DEBRIDEMENT: Urea gel loosens necrotic tissue
   
4. MOISTURIZER: Low conc. (5-10%) retains skin moisture (humectant)

5. NITROGEN SUPPLEMENT: In parenteral nutrition (renal failure)

6. DIAGNOSTIC: ¹³C-Urea Breath Test for H. pylori detection
   Patient drinks ¹³C-labeled urea → H. pylori urease cleaves it
   → ¹³CO₂ in breath = positive for H. pylori

7. HAIR TREATMENT: Relaxing agents contain urea (breaks H-bonds in hair)

8. ANTIFUNGAL NAIL TREATMENT: 40% urea paste for nail avulsion

---

Storage

Store in well-closed containers, protected from light and moisture.
Urea is stable but hydrolyzes slowly in water to NH₃ + CO₂.

---

Q2. Benzyl Alcohol — Preparation, Purity Test and Medicinal Uses (10 Marks)

Introduction

Benzyl Alcohol (phenylmethanol) is an aromatic alcohol with formula C₆H₅—CH₂OH. It is a clear, colorless liquid with a mild pleasant aromatic odor.

Structure:
      CH₂—OH
       |
   [benzene ring]
   C₆H₅CH₂OH

Molecular formula: C₇H₈O
Molecular weight: 108.14 g/mol
Boiling point: 205°C
Appearance: Colorless liquid
Solubility: Slightly soluble in water, miscible with organic solvents

---

Preparation of Benzyl Alcohol

2 C₆H₅CHO  ──[conc. NaOH]──→  C₆H₅CH₂OH  +  C₆H₅COONa
(benzaldehyde)                  (benzyl alcohol)  (sodium benzoate)

No α-H → Cannizzaro (disproportionation)
One molecule oxidized, one reduced.

C₆H₅CH₂Cl  +  NaOH (aq)  →  C₆H₅CH₂OH  +  NaCl
(benzyl chloride)              (benzyl alcohol)

SN2 mechanism: OH⁻ displaces Cl⁻

C₆H₅CHO  ──[NaBH₄ or LiAlH₄]──→  C₆H₅CH₂OH
(benzaldehyde)                       (benzyl alcohol)

Or:
C₆H₅COOH  ──[LiAlH₄]──→  C₆H₅CH₂OH
(benzoic acid)               (benzyl alcohol)

C₆H₅MgBr  +  HCHO  →  C₆H₅CH₂OMgBr  ──[H₃O⁺]──→  C₆H₅CH₂OH
(Grignard)  (formaldehyde)                            (benzyl alcohol)

---

Purity Tests for Benzyl Alcohol (IP/BP)

Pure benzyl alcohol: n₂₀D = 1.539-1.541
Test: Abbe refractometer at 20°C

Range: 1.043-1.049 at 20°C
Test: Density bottle or pycnometer

Pure BP: 203-207°C (BP range)
Test: Distillation (90% should distill within 2°C range)

Add potassium permanganate (KMnO₄) in sulfuric acid:
Pure benzyl alcohol: does NOT decolorize KMnO₄ rapidly
If decolorizes quickly → benzaldehyde impurity present

Or: Schiff's test → pink/magenta color if aldehyde present

Dissolve in ethanol → add phenolphthalein → should not turn pink
(no acidic impurity = benzoic acid)
NMT 0.05% of benzoic acid allowed

NMT 0.1% water

Benzyl alcohol can oxidize on storage → benzaldehyde/benzoic acid/peroxides
Test: KI solution → should not turn yellow (no peroxides)
Or: Starch-iodide paper should not turn blue

+ AgNO₃ → no white ppt (chloride absent; would indicate benzyl chloride impurity)

---

Medicinal Uses of Benzyl Alcohol

1. PRESERVATIVE: Most important pharmaceutical use
   Used as bacteriostatic preservative in multi-dose injections (0.9-1.5% conc.)
   Active against gram-positive bacteria
   Examples: Injectable solutions, eye drops (sometimes)

2. ANTIPARASITIC (Topical): 5% benzyl alcohol lotion
   Used for HEAD LICE treatment (pediculosis capitis)
   MOA: Asphyxiates lice by blocking respiratory spiracles
   Brand: Ulesfia (5% lotion)

3. LOCAL ANESTHETIC: Mild local anesthetic and antipruritic
   Used in lip balms, topical preparations

4. SOLVENT/EXCIPIENT in pharmaceutical formulations:
   - Injectable preparations
   - Cosmetics and perfumes (fragrance fixative)
   - Topical creams and lotions

5. ANTISEPTIC: mild antiseptic activity in mouthwashes

6. PAIN RELIEF: Minor topical analgesic in dental preparations

---

Q3. Benzaldehyde — Preparation, Purity Test and Medicinal Uses (10 Marks)

Introduction

Benzaldehyde (benzenecarbaldehyde) has formula C₆H₅—CHO. It is the simplest aromatic aldehyde — a colorless liquid with a characteristic almond/cherry odor.

Structure:
      CHO
       |
   [benzene ring]
   C₆H₅—CHO

Molecular formula: C₇H₆O
Molecular weight: 106.12 g/mol
Boiling point: 178-179°C
Appearance: Colorless to pale yellow liquid
Odor: Characteristic almond-like odor

---

Preparation of Benzaldehyde

C₆H₅CH₂OH  ──[MnO₂ or CrO₃]──→  C₆H₅CHO  +  H₂O
(benzyl alcohol)                    (benzaldehyde)

Selective oxidation of primary benzylic alcohol to aldehyde (not over-oxidized to acid)

C₆H₅CHCl₂  +  H₂O  ──[Ca(OH)₂]──→  C₆H₅CHO  +  2HCl
(benzal chloride)                      (benzaldehyde)

Benzal chloride obtained by: C₆H₅CH₃ + 2Cl₂/hν → C₆H₅CHCl₂

C₆H₆  +  CO  +  HCl  ──[AlCl₃/CuCl]──→  C₆H₅CHO  +  HCl
(benzene)                                  (benzaldehyde)

[H—C≡O]⁺ (formyl cation) is the electrophile in this EAS reaction

C₆H₅COCl  +  H₂  ──[Pd/BaSO₄ catalyst]──→  C₆H₅CHO  +  HCl
(benzoyl chloride)   (poisoned catalyst)       (benzaldehyde)

Poisoned Pd (BaSO₄/quinoline) prevents over-reduction to benzyl alcohol.

C₆H₅CH₃  ──[MnO₂/H₂SO₄ or air/catalyst]──→  C₆H₅CHO
(toluene)                                       (benzaldehyde)

---

Purity Tests for Benzaldehyde (IP/BP)

Pure benzaldehyde: n₂₀D = 1.544-1.546
Test: Refractometer at 20°C

Range: 1.041-1.046 at 20°C

Not less than 97% should distill between 177-182°C

Heat with 10% NaOH, filter, acidify, add AgNO₃
→ No white precipitate (no residual benzal chloride/benzaldehyde chloride)

Benzaldehyde oxidizes on storage → benzoic acid (impurity)
Test: Add ether solution to Na₂CO₃ → shake → acidify aqueous layer
→ No precipitate of benzoic acid should form
OR: Dissolve in NaOH → should be clear (benzoic acid would form sodium benzoate ppt)
Limit: NMT 0.05% benzoic acid

1% KI in acetic acid → no liberation of iodine (no peroxides)
(Peroxides form on oxidation of benzaldehyde by O₂)

Benzaldehyde + NH₂OH·HCl → Benzaldoxime + HCl
The HCl is titrated with NaOH
% C₆H₅CHO = calculated from titration
IP: NLT 98.0% benzaldehyde

+ Fehling's solution → Red-brown ppt of Cu₂O (reduces Fehling's, unlike ketones)
Confirms aldehyde group present.

---

Medicinal Uses of Benzaldehyde

1. FLAVORING AGENT (most important): Almond flavor in food
   Used in food and pharmaceutical formulations as flavoring

2. PHARMACEUTICAL INTERMEDIATE:
   - Synthesis of ampicillin (semisynthetic penicillin)
   - Synthesis of cinnamaldehyde
   - Synthesis of mandelic acid

3. ANTIMICROBIAL: Minor antimicrobial activity
   Used in some topical preparations

4. ANTI-TUMOR (experimental): Some studies on antitumor activity
   Benzaldehyde and its derivatives investigated for anticancer properties

5. ANTIPARASITIC: Some antiparasitic activity

6. PERFUMERY and COSMETICS: Major use in fragrances
   (Not strictly medicinal, but pharmaceutical excipient)

7. SOLVENT: In pharmaceutical synthesis processes

---

Q4. Chlorobutanol — Preparation, Purity Test and Assay (10 Marks)

Introduction

Chlorobutanol (trichloro-tert-butanol; chlorbutol) is an organohalogen compound with formula (CH₃)₂C(OH)CCl₃ (1,1,1-trichloro-2-methyl-2-propanol). It is a white crystalline solid used as a preservative and mild sedative.

Structure:
      CH₃  OH
       |   |
  Cl₃C—C
       |
      CH₃

More precisely:
CCl₃—C(CH₃)₂—OH

Molecular formula: C₄H₇Cl₃O
Molecular weight: 177.46 g/mol
Melting point: 95-98°C (anhydrous); 76-78°C (hemihydrate)
Appearance: White crystalline solid
Odor: Camphor-like odor

---

Preparation of Chlorobutanol

      O                    OH
      ‖         KOH         |
CH₃—C—CH₃  +  CHCl₃  ──────────→  Cl₃C—C—CH₃
(acetone)   (chloroform)   (10-15°C)        |
                                           CH₃
                                      (chlorobutanol)

Step 1: KOH deprotonates CHCl₃ → trichlorocarbanion :CCl₃⁻

   CHCl₃  +  KOH  →  :CCl₃⁻  +  K⁺  +  H₂O

Step 2: :CCl₃⁻ attacks carbonyl carbon of acetone (nucleophilic addition)

          O                       O⁻
          ‖       :CCl₃⁻           |
   CH₃—C—CH₃  ──────────→  Cl₃C—C—CH₃
                                    |
                                   CH₃
                            (alkoxide intermediate)

Step 3: Protonation → chlorobutanol

   Cl₃C—C(CH₃)₂—O⁻  +  H₂O  →  Cl₃C—C(CH₃)₂—OH  +  OH⁻
                                    (chlorobutanol)

---

Properties

Chlorobutanol:
- Hemihydrate form: MP 76-78°C (unstable, common form)
- Anhydrous form: MP 95-98°C
- Sublimes slowly at room temperature
- Slightly volatile → camphor-like smell
- Solubility: 0.8 g/100mL water; soluble in alcohol, ether

---

Purity Tests for Chlorobutanol (IP/BP/USP)

Anhydrous form: 97-100°C
(Hemihydrate: 76-78°C)
Test: Capillary method

Test A (Chloride): 
Dissolve in alcohol + NaOH (aqueous, heat)
→ Cool → add dilute HNO₃ → add AgNO₃
→ White precipitate of AgCl (confirms organic chlorine)
C₃H₇Cl → HCl → AgCl ↓ (white)

Test B (Ketone test):
On heating with H₂SO₄, chlorobutanol decomposes → chloroform + acetone
→ Smell of chloroform
→ Sodium nitroprusside + NaOH → red color (confirms acetone)

Test C (Camphor-like odor + melting point): Characteristic

Dissolve 1g in 20 mL water (warm):
→ Add phenolphthalein indicator
→ Should not turn pink (not alkaline)
→ Should not require >0.3 mL of 0.01M NaOH (not acidic)

Dissolve in water → add AgNO₃
→ No immediate white precipitate (no free ionic chloride)
(Organic chlorine only - will not precipitate directly with AgNO₃)

Hemihydrate: Allowed 5.5-6.5% water
Anhydrous: NMT 0.5% loss
Dry at 50°C under vacuum for 3 hours

Limit: NMT 20 ppm
Test by standard heavy metal limit test

NMT 0.1%

---

Assay of Chlorobutanol

CCl₃—C(CH₃)₂—OH  +  3NaOH  ──[heat]──→  CHCl₃ + (CH₃)₂C(OH)—ONa
                                          ↓
                               Chloroform is lost
                               
Actually, full hydrolysis:
CCl₃—C(CH₃)₂—OH + 4NaOH → 3NaCl + (CH₃)₂C(OH)COONa + H₂O
(chlorobutanol)             (sodium chloride - titrated)

Method A: Mohr's Method (direct titration)
   - Titrate with AgNO₃ (standardized, 0.1 M)
   - Indicator: Potassium chromate (K₂CrO₄) - brick-red endpoint
   
   Ag⁺ + Cl⁻ → AgCl ↓ (white precipitate, quantitative)
   Endpoint: Red-brown color (Ag₂CrO₄ forms when Cl⁻ exhausted)

Method B: Volhard's Method (back titration)
   - Add excess AgNO₃
   - Titrate back with ammonium thiocyanate (NH₄SCN)
   - Indicator: Ferric alum (Fe³⁺)
   - Endpoint: Red color (FeSCN²⁺)

% Chlorobutanol = (Titre × Molarity × Eq. weight × dilution factor × 100) / Weight of sample

Molecular weight of chlorobutanol = 177.46
1 mole gives 3 moles Cl (after complete hydrolysis)
Equivalent weight = 177.46 / 3 = 59.15

% Chlorobutanol = (Titre (mL) × 0.1 × 59.15 × 100) / (weight in mg)

---

Medicinal Uses of Chlorobutanol

1. PRESERVATIVE (Primary use): 0.5% concentration
   Used in: Ophthalmic (eye) drops, ear drops, nasal sprays,
            injectable preparations, cosmetics
   Active against: Bacteria and fungi
   Advantages: Non-irritating to mucous membranes

2. MILD SEDATIVE/HYPNOTIC (historical):
   Was used as a mild sedative (acts like chloral hydrate)
   MOA: CNS depressant, similar to chloroform/chloral hydrate
   Now largely replaced by safer agents

3. LOCAL ANESTHETIC: Very mild local anesthetic properties
   Used in some dental preparations

4. DENTAL PREPARATIONS: Minor analgesic in toothache preparations

5. ANTIDOTE: Minor use in nausea/vomiting preparations

6. VETERINARY USE: Preservative in veterinary injections

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═══════════════════════════════════════

UNITS 7-10 QUICK REVISION CARD

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╔══════════════════════════════════════════════════════════════════════╗
║         ORGANIC CHEMISTRY UNITS 7-10 — EXAM QUICK REVISION         ║
╠══════════════════════════════════════════════════════════════════════╣
║ UNIT 7 - AROMATIC CHEMISTRY                                         ║
║ Halogens: Deactivating (-I) BUT ortho/para directing (+M)           ║
║ Benzyl radical: 4 resonance structures, most stable radical (BDE=85)║
║ Free radical Friedel-Crafts: R• attacks ring → cyclohexadienyl     ║
║ EAS orientation: o/p = electron-donating; meta = electron-withdrawing║
╠══════════════════════════════════════════════════════════════════════╣
║ UNIT 8 - CONDENSATION REACTIONS                                     ║
║ Cross Aldol: use component with NO α-H as electrophile              ║
║   (benzaldehyde + acetaldehyde → cinnamaldehyde)                    ║
║ Perkin: ArCHO + (RCH₂CO)₂O + RCH₂COONa → α,β-unsaturated acid    ║
║ Cannizzaro: no α-H + conc. NaOH → 50% acid + 50% alcohol           ║
║   Key step: HYDRIDE (H⁻) TRANSFER (not proton!)                    ║
╠══════════════════════════════════════════════════════════════════════╣
║ UNIT 9 - NAMED REACTIONS                                            ║
║ Williamson: RONa + R'X(primary) → R-O-R' + NaX (SN2)              ║
║ Fries: Phenyl ester + AlCl₃ → o-hydroxy (high T) or p- (low T)    ║
║ Kolbe: PhONa + CO₂ → salicylate (Na → ortho; K → para)            ║
║ Reimer-Tiemann: PhOH + CHCl₃ + NaOH → :CCl₂ → salicylaldehyde    ║
╠══════════════════════════════════════════════════════════════════════╣
║ UNIT 10 - PHARMACEUTICAL                                            ║
║ Urea: NH₃+CO₂→urea | Xanthydrol test | diuretic, keratolytic       ║
║ Benzyl alcohol: Cannizzaro/hydrolysis | refractive index | preserv. ║
║ Benzaldehyde: oxidation/hydrolysis | Rosenmund | flavoring agent    ║
║ Chlorobutanol: CHCl₃+acetone+KOH | assay=AgNO₃ titration | preserv.║
╚══════════════════════════════════════════════════════════════════════╝

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🧪 ORGANIC CHEMISTRY — MASTER QUICK REVISION

All Units 1-10 | Pharm D 1st Year | Simple Language

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╔══════════════════════════════════════╗

║ UNIT 1 — BASICS ║

╚══════════════════════════════════════╝

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🔑 ACID-BASE THEORIES (One Line Each)

Memory trick:
Arrhenius = WATER ONLY
Bronsted = PROTON TRANSFER
Lewis = ELECTRON PAIR (BROADEST - most important in organic)

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🔑 INTERMOLECULAR FORCES (Weakest → Strongest)

London Dispersion < Dipole-Dipole < Hydrogen Bond < Ion-Dipole

LDF = all molecules (temporary dipoles)
Dipole-Dipole = polar molecules (HCl, HBr)
H-Bond = N-H, O-H, F-H only (strongest IMF between molecules)
Ion-Dipole = NaCl in water (strongest of all)

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🔑 BP, MP, SOLUBILITY

BOILING POINT: Temperature where liquid becomes gas
→ More IMF = Higher BP
→ Larger molecule = Higher BP

MELTING POINT: Temperature where solid becomes liquid
→ More symmetric molecule = Higher MP (better packing in crystal)

SOLUBILITY: "Like dissolves like"
→ Polar + Polar = Soluble (NaCl in water)
→ Nonpolar + Nonpolar = Soluble (oil in hexane)
→ Polar + Nonpolar = INSOLUBLE

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🔑 DIPOLE MOMENT

μ = q × d       (charge × distance)
Unit = Debye (D)

Key rules:
- Symmetric molecules → dipoles CANCEL → μ = 0 (CO₂, CCl₄)
- Asymmetric molecules → dipoles ADD → μ ≠ 0 (H₂O = 1.85D, HCl = 1.08D)
- Higher electronegativity difference = Higher μ
- Lone pairs contribute to μ

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🔑 ISOMERISM

STRUCTURAL ISOMERS = same formula, different connectivity

Type          What differs          Example (C₅H₁₂)
Chain         Skeleton (straight    n-pentane vs neopentane
              vs branched)
Position      Where functional      1-Br-propane vs 2-Br-propane
              group sits
Functional    Different group       C₂H₆O: ethanol vs dimethyl ether
Metamerism    Alkyl groups on       Diethyl ether vs methyl propyl ether
              same functional group
Tautomerism   Dynamic equilibrium   Keto ⇌ Enol (acetoacetic ester)
Ring-Chain    Ring vs open chain    Cyclopropane vs propene (C₃H₆)

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╔══════════════════════════════════════╗

║ UNIT 2 — CLASSIFICATION ║

╚══════════════════════════════════════╝

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🔑 ORGANIC CHEMISTRY

= Study of carbon-containing compounds
Wohler (1828): First made urea in lab from inorganic material
→ Disproved "Vital Force Theory"

Why carbon is special:
1. Tetravalency (4 bonds)
2. Catenation (C-C-C long chains)
3. Forms single, double, triple bonds

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🔑 CLASSIFICATION TREE

ORGANIC COMPOUNDS
├── ACYCLIC (open chain / aliphatic)
│   ├── Saturated: Alkanes (CₙH₂ₙ₊₂) - only single bonds
│   └── Unsaturated: Alkenes (CₙH₂ₙ) / Alkynes (CₙH₂ₙ₋₂)
└── CYCLIC (ring)
    ├── Alicyclic: Ring but NOT aromatic (Cyclohexane)
    └── Aromatic: Benzene ring (delocalized e⁻)
        ├── Benzenoid: Benzene, Toluene, Naphthalene
        └── Non-benzenoid: Azulene

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🔑 IUPAC NAMES

ALDEHYDES: longest chain with CHO → replace '-e' with '-al'
  HCHO = Methanal     CH₃CHO = Ethanal
  CH₃CH₂CHO = Propanal   C₆H₅CHO = Benzaldehyde

AMINES: longest chain with NH₂ → replace '-e' with '-amine'
  CH₃NH₂ = Methanamine       C₂H₅NH₂ = Ethanamine
  (CH₃)₂NH = N-methylmethanamine    C₆H₅NH₂ = Benzenamine (Aniline)
  Secondary/Tertiary: use prefix N- for groups on nitrogen

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🔑 FREE RADICAL CHAIN REACTION

3 STAGES (must memorize):

1. INITIATION: ROOR → 2RO• → Br•   (heat/UV breaks peroxide)

2. PROPAGATION (repeats 10,000 times):
   Br• + alkene → carbon radical
   Carbon radical + HBr → product + Br•

3. TERMINATION: radical + radical → stable product → CHAIN STOPS

KEY PRODUCT: ANTI-MARKOVNIKOV (Br adds to less substituted carbon)

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🔑 RADICAL STABILITY

Most stable → Least stable:
Benzylic > Allylic > Tertiary (3°) > Secondary (2°) > Primary (1°) > Methyl

Why? More alkyl groups = more hyperconjugation = more stable radical
BDE of C-H: Benzylic (85) < Tertiary (91) < Secondary (96) < Primary (100)
Lower BDE = weaker bond = more stable radical forms

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╔══════════════════════════════════════╗

║ UNIT 3 — SN1, SN2, CARBOCATIONS ║

╚══════════════════════════════════════╝

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🔑 SN2 vs SN1 — MASTER COMPARISON

┌─────────────────┬──────────────────────┬──────────────────────┐
│                 │ SN2                  │ SN1                  │
├─────────────────┼──────────────────────┼──────────────────────┤
│ Steps           │ ONE step (concerted) │ TWO steps            │
│ Rate law        │ k[substrate][Nu]     │ k[substrate]         │
│ Intermediate    │ NONE (only TS)       │ CARBOCATION          │
│ Best substrate  │ Methyl / Primary     │ Tertiary             │
│ Stereochemistry │ INVERSION (Walden)   │ RACEMIZATION         │
│ Solvent         │ Polar APROTIC (DMSO) │ Polar PROTIC (H₂O)   │
│ Nucleophile     │ STRONG needed        │ Weak is OK           │
│ Rearrangement   │ NO                   │ YES (cation forms)   │
└─────────────────┴──────────────────────┴──────────────────────┘

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🔑 NUCLEOPHILES & LEAVING GROUPS

NUCLEOPHILE = electron pair DONOR (attacks electrophilic C)
Good Nu: OH⁻, CN⁻, I⁻, RS⁻, RO⁻ (strong bases, negative charge)
Poor Nu: H₂O, ROH (neutral, weak)

LEAVING GROUP = departs with electron pair
Good LG (weak bases): I⁻ > Br⁻ > Cl⁻ >> F⁻ > OH⁻
(Good LG = stable after leaving = weak base)
Bad LG: OH⁻, NH₂⁻ (must be protonated first!)

STERIC HINDRANCE:
Methyl: open → SN2 easy ✓
Primary: slight block → SN2 fast ✓
Secondary: moderate → SN2 slower
Tertiary: totally blocked → NO SN2 → SN1 only

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🔑 CARBOCATIONS

STABILITY: Benzylic > Allylic > 3° > 2° > 1° > Methyl (most → least stable)

REARRANGEMENTS (shift toward more stable cation):
1. Hydride shift (H⁻ migrates): 1° → 2° or 2° → 3°
2. Methyl shift: 1° → 3° (neopentyl type)

Rule: ALWAYS shifts to form MORE STABLE carbocation!
Only happens in SN1/E1 (not in SN2/E2 = no carbocation)

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╔══════════════════════════════════════╗

║ UNIT 4 — E1 & E2 ELIMINATION ║

╚══════════════════════════════════════╝

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🔑 E1 vs E2 — QUICK TABLE

┌─────────────────┬──────────────────────┬──────────────────────┐
│                 │ E1                   │ E2                   │
├─────────────────┼──────────────────────┼──────────────────────┤
│ Steps           │ TWO (stepwise)       │ ONE (concerted)      │
│ Rate law        │ k[substrate]         │ k[substrate][base]   │
│ Intermediate    │ CARBOCATION          │ NONE                 │
│ Base needed     │ Weak base OK         │ STRONG base needed   │
│ Best substrate  │ Tertiary             │ Secondary/Tertiary   │
│ Geometry needed │ None                 │ ANTI-PERIPLANAR (H   │
│                 │                      │ and LG at 180°)      │
│ Stereochemistry │ E + Z mixture        │ Stereospecific       │
│ Solvent         │ Polar protic         │ Polar aprotic/protic │
│ Rearrangement   │ YES                  │ NO                   │
└─────────────────┴──────────────────────┴──────────────────────┘

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🔑 ORIENTATION RULES

ZAITSEV'S RULE: More substituted alkene = MAJOR product
(applies to E1 always; E2 with small base)

HOFMANN'S RULE: Less substituted alkene = MAJOR product
(applies to E2 with BULKY base like t-BuOK)

Simple way to remember:
Small base → Zaitsev (attacks hindered β-H)
Bulky base → Hofmann (cannot reach hindered β-H → attacks easy β-H)

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🔑 E vs SN — WHICH ONE WINS?

High temperature + strong base + tertiary → E2 wins
Low temperature + strong small Nu + primary + aprotic → SN2 wins
Polar protic + tertiary + weak Nu + heat → SN1/E1 compete
Bulky base + any substrate → E2 wins over SN2

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🔑 DEHYDRATION OF ALCOHOLS

ROH + H⁺/heat → Alkene + H₂O   (E1 mechanism for 3° and 2°)

Ease of dehydration:
3° ROH > 2° ROH > 1° ROH   (same order as carbocation stability)

Mechanism (E1):
Step 1: OH gets protonated → H₂O (good leaving group!)
Step 2: H₂O leaves → carbocation (RDS)
Step 3: Base removes β-H → alkene

Zaitsev rule applies → more substituted alkene is major product
Rearrangement can happen (via carbocation intermediate)

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╔══════════════════════════════════════╗

║ UNIT 5 — PEROXIDE EFFECT & MARKOV ║

╚══════════════════════════════════════╝

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🔑 MARKOVNIKOV'S RULE

"H goes to the carbon with MORE hydrogens"
(Modern: H adds to give MORE STABLE carbocation)

CH₃CH=CH₂ + HBr → CH₃CHBrCH₃   (2-bromopropane)
                    ↑
                 Markovnikov product (no peroxide)

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🔑 PEROXIDE EFFECT (KHARASCH EFFECT)

With peroxide: ANTI-MARKOVNIKOV product forms
CH₃CH=CH₂ + HBr + ROOR → CH₃CH₂CH₂Br   (1-bromopropane)

WHY ONLY HBr? (Very important exam question!)
HCl: step 2 is ENDOTHERMIC → no chain
HBr: BOTH steps exothermic → chain works ✓
HI: step 1 is ENDOTHERMIC → no chain

REMEMBER: ONLY HBr shows peroxide effect!

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🔑 FREE RADICAL ADDITION — 3 STAGES

INITIATION:  ROOR →[hν]→ RO• → Br•

PROPAGATION (CYCLE - repeats 10,000+ times):
  Step A: Br• + C=C → BrC-C•   (Br• adds to LESS substituted C)
  Step B: BrC-C• + HBr → product + Br•  (H from HBr joins)

TERMINATION:
  Br• + Br• → Br₂ (chain stops when two radicals meet)

RESULT: Br adds to LESS substituted C → ANTI-MARKOVNIKOV

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🔑 HALOGENATION — REACTIVITY vs SELECTIVITY

REACTIVITY (speed):   F• > Cl• > Br• > I•
SELECTIVITY (choosy): I• > Br• > Cl• > F•

These are OPPOSITE! More reactive = less selective.

Br• is most useful: selective (attacks only weakest 3° C-H)
Cl• is less useful: non-selective (attacks all C-H bonds)

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╔══════════════════════════════════════╗

║ UNIT 6 — ADVANCED FREE RADICALS ║

╚══════════════════════════════════════╝

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🔑 ALLYLIC HALOGENATION (NBS)

NBS = N-Bromosuccinimide
Used for: SELECTIVE bromination at ALLYLIC position (C next to C=C)

Why allylic? Allylic C-H is weakest (BDE ≈ 88 kcal/mol)
Allylic radical is RESONANCE STABILIZED (•CH₂-CH=CH₂ ↔ CH₂=CH-CH₂•)

Conditions: NBS + CCl₄ + hν (UV light) or ROOR
Product: Allylic bromide

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🔑 NUCLEOPHILIC SUBSTITUTION IN ALLYLIC SUBSTRATES

Allylic C+ is delocalized → forms allylic cation
→ Nu can attack EITHER end of delocalized cation → TWO products!

SN1' = SN1 with allylic rearrangement (product at different carbon)
SN2  = direct attack (primary allylic, polar aprotic, strong Nu)
SN2' = attack at other end of allyl system (rearranged SN2)

Example: CH₃CH=CH-CH₂Cl + H₂O
→ Direct product: CH₃CH=CH-CH₂OH
→ Rearranged product: CH₃CH(OH)-CH=CH₂
(Both can form in SN1' via delocalized cation)

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🔑 CONJUGATED DIENES — 1,2 vs 1,4 ADDITION

Conjugated diene = C=C-C=C (alternating double bonds)
Example: 1,3-Butadiene: CH₂=CH-CH=CH₂

When HBr adds:
1,2-ADDITION: Br adds to C1, H adds to C2 → terminal alkene remains
1,4-ADDITION: Br adds to C1, H adds to C4 → internal alkene (more stable)

TEMPERATURE RULE:
Low temperature (-80°C) → 1,2-product MAJOR (kinetic = faster)
High temperature (40°C) → 1,4-product MAJOR (thermodynamic = more stable)

Key: Low T = kinetic control; High T = thermodynamic control

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🔑 SUBSTITUTION vs ADDITION (FREE RADICAL) — QUICK COMPARE

SUBSTITUTION               ADDITION
Substrate = ALKANE         Substrate = ALKENE
C-H bond breaks            C=C bond breaks
H replaced by X            HX adds across double bond
Conditions: X₂ + hν       Conditions: HBr + peroxide/hν
Product: R-X + HX          Product: Anti-Markovnikov product
Example: CH₄+Cl₂→CH₃Cl    Example: CH₃CH=CH₂+HBr→CH₃CH₂CH₂Br
Same mechanism: Init.→Prop.→Term. (both are chain reactions)

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╔══════════════════════════════════════╗

║ UNIT 7 — AROMATIC & EAS ║

╚══════════════════════════════════════╝

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🔑 HALOGENS IN EAS

Halogens (F, Cl, Br, I) have TWO opposing effects:

-I effect (inductive): withdraws e⁻ from ring → DEACTIVATES ring
+M effect (mesomeric): lone pair donates INTO ring → ORTHO/PARA director

RESULT: DEACTIVATING but ORTHO/PARA DIRECTING
(This is the UNUSUAL combination - most deactivators are META directors)

Rate: Chlorobenzene reacts SLOWER than benzene
Position: Electrophile goes to ORTHO and PARA of halogen

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🔑 BENZYL RADICAL STABILITY

C₆H₅-CH₂• (benzyl radical)

WHY MOST STABLE?
→ Unpaired electron overlaps with benzene π system
→ Delocalized over 4 positions (CH₂ + 2 ortho + para)
→ 4 resonance structures

BDE of benzylic C-H = 85 kcal/mol (LOWEST = weakest bond = most stable radical)

Consequence: Free radical reactions attack BENZYLIC position first
(NBS + toluene → benzyl bromide selectively)

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🔑 EAS — DIRECTING GROUPS SUMMARY

ACTIVATING (ring more reactive than benzene):
Strong: -NH₂, -OH, -OR → ortho/para directors
Weak: -CH₃, alkyl → ortho/para directors

DEACTIVATING (ring less reactive than benzene):
Special: -F, -Cl, -Br, -I → ortho/para directors (unusual!)
Strong: -NO₂, -CN, -COOH, -CHO → META directors

MEMORY TRICK:
All deactivating groups are META directors...
EXCEPT HALOGENS (which are o/p despite deactivating)

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🔑 EAS MECHANISM — 2 STEPS

Step 1: E⁺ attacks ring → ARENIUM ION (Wheland intermediate)
        Ring loses aromaticity → sp3 carbon at attack site
        This is the SLOW step (rate-determining)

Step 2: H⁺ leaves → ring re-aromatizes
        This is the FAST step

The ARENIUM ION stability determines which position is attacked.
More stable arenium = faster reaction = preferred position.

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╔══════════════════════════════════════╗

║ UNIT 8 — CONDENSATION REACTIONS ║

╚══════════════════════════════════════╝

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🔑 CROSS ALDOL CONDENSATION

ALDOL = Aldehyde + Alcohol (product has both groups)

CROSS ALDOL: Two DIFFERENT compounds react
KEY TRICK: Use one compound with NO α-H as electrophile
           (cannot form enolate → acts only as acceptor)

No α-H examples: Benzaldehyde (C₆H₅CHO), Formaldehyde (HCHO)

Classic reaction:
C₆H₅CHO + CH₃CHO →[NaOH]→ C₆H₅CH=CHCHO + H₂O
(benzaldehyde) (acetaldehyde)      (cinnamaldehyde)

Steps: 1. Base removes α-H → enolate
       2. Enolate attacks electrophilic C=O → aldol
       3. Dehydration → α,β-unsaturated product (conjugated = stable)

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🔑 PERKIN CONDENSATION

ArCHO + (RCH₂CO)₂O + RCH₂COONa → ArCH=CR-COOH + RCH₂COOH

Reagents: Aromatic aldehyde + Acid anhydride + Salt of same acid
Product: α,β-Unsaturated carboxylic acid

Classic: C₆H₅CHO + (CH₃CO)₂O + CH₃COONa → Cinnamic acid
Conditions: 150-200°C (high temperature)

Steps: Salt removes α-H from anhydride → carbanion → attacks ArCHO → 
       dehydration → cinnamic acid

REMEMBER: Only AROMATIC aldehydes (no α-H) react cleanly

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🔑 CANNIZZARO REACTION

Requirement: Aldehyde with NO α-H + conc. NaOH

What happens: One molecule OXIDIZED → acid (salt)
              One molecule REDUCED → alcohol

2 C₆H₅CHO + NaOH → C₆H₅COONa + C₆H₅CH₂OH
(benzaldehyde)    (sodium benzoate) (benzyl alcohol)

KEY STEP: HYDRIDE TRANSFER (H⁻, not proton H⁺!)
- OH⁻ adds to one CHO → activated donor
- H⁻ migrates to second CHO → reduces it to alcohol

CROSS CANNIZZARO: HCHO always gets REDUCED to CH₃OH
(formaldehyde most reactive → preferentially reduced)

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╔══════════════════════════════════════╗

║ UNIT 9 — NAMED REACTIONS ║

╚══════════════════════════════════════╝

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🔑 WILLIAMSON SYNTHESIS

MAKES: Ethers (both symmetric and unsymmetrical)

ROH + Na → RO⁻Na⁺ (alkoxide) → + R'X → R-O-R' + NaX

RULE: R'X MUST be PRIMARY alkyl halide (SN2 mechanism)
Tertiary R'X → ONLY elimination (E2), no ether formed!

Examples:
CH₃O⁻ + C₂H₅Br → CH₃OC₂H₅ (methyl ethyl ether) ✓
CH₃O⁻ + (CH₃)₃CBr → only isobutylene (E2) ✗

For aryl ethers:
C₆H₅O⁻Na⁺ + CH₃I → C₆H₅OCH₃ (anisole)

---

🔑 FRIES REARRANGEMENT

CONVERTS: Phenyl ester → Hydroxy aryl ketone
REAGENT: AlCl₃ (Lewis acid catalyst)
MECHANISM: AlCl₃ breaks C-O bond → acylium ion (R-CO⁺) → EAS on ring

     OC(O)R              OH
      |     AlCl₃         |
   [ring] ────────→   [ring]-COR  (o- and/or p-)

TEMPERATURE EFFECT:
LOW temperature → PARA product (thermodynamic)
HIGH temperature → ORTHO product (kinetic/intramolecular)

Photo-Fries: Same reaction with UV light (no AlCl₃ needed)

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🔑 KOLBE REACTION (Kolbe-Schmitt)

MAKES: Salicylic acid (used to make aspirin!)

C₆H₅ONa + CO₂ →[125°C, 4-7 atm]→ HOC₆H₄COONa →[H⁺]→ Salicylic acid

CATION EFFECT:
Sodium phenoxide (Na⁺) → ORTHO product (salicylic acid)
Potassium phenoxide (K⁺) → PARA product (p-hydroxybenzoic acid)

Why? Na⁺ (small) chelates → CO₂ attacks ortho
     K⁺ (large) cannot chelate → CO₂ attacks para

Importance: Salicylic acid + acetic anhydride → ASPIRIN

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🔑 REIMER-TIEMANN REACTION

MAKES: Salicylaldehyde (ortho-hydroxybenzaldehyde)

C₆H₅OH + CHCl₃ + NaOH → C₆H₄(OH)(CHO) + other products
(phenol)  (chloroform)      (salicylaldehyde - MAJOR)

KEY INTERMEDIATE: DICHLOROCARBENE (:CCl₂)
CHCl₃ + NaOH → :CCl₂ + NaCl + H₂O
:CCl₂ is an electrophilic carbene → attacks ring at ORTHO

Steps:
1. CHCl₃ + NaOH → :CCl₂ (carbene)
2. Phenol + NaOH → phenoxide (C₆H₅O⁻)
3. :CCl₂ attacks ortho C of phenoxide
4. NaOH hydrolyzes -CHCl₂ → -CHO
Product: Salicylaldehyde (MAJOR, ortho) + p-hydroxybenzaldehyde (minor)

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╔══════════════════════════════════════╗

║ UNIT 10 — PHARMACEUTICALS ║

╚══════════════════════════════════════╝

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🔑 UREA — QUICK FACTS

Formula: NH₂-CO-NH₂    MW: 60.06    MP: 132-135°C

PREPARATION:
Industrial: NH₃ + CO₂ →[150-200°C, 150atm]→ NH₂COONH₄ → Urea
Historical (Wohler): NH₄CNO → Urea (first organic synthesis!)

PURITY TESTS:
✓ MP: 132-135°C
✓ Xanthydrol test: White precipitate of dixanthyl urea (SPECIFIC)
✓ Nitrogen content: 46.3-46.6% (Kjeldahl method)
✓ Loss on drying: NMT 1%

MEDICINAL USES:
→ Osmotic diuretic (brain edema, glaucoma)
→ Keratolytic (10-40% cream for dry/hard skin)
→ H. pylori test (¹³C-urea breath test)
→ Moisturizer (5% humectant)
→ Nail treatment (40% paste)

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🔑 BENZYL ALCOHOL — QUICK FACTS

Formula: C₆H₅CH₂OH    MW: 108.14    BP: 205°C

PREPARATION:
1. Cannizzaro: 2C₆H₅CHO + NaOH → C₆H₅CH₂OH + C₆H₅COONa
2. Hydrolysis: C₆H₅CH₂Cl + NaOH → C₆H₅CH₂OH
3. Reduction: C₆H₅CHO + NaBH₄ → C₆H₅CH₂OH

PURITY TESTS:
✓ Refractive index: 1.539-1.541
✓ Specific gravity: 1.043-1.049
✓ Peroxide test: KI solution → no yellow color
✓ Aldehyde test: No Schiff's reagent color (no benzaldehyde impurity)

MEDICINAL USES:
→ Bacteriostatic PRESERVATIVE (0.9-1.5% in injections)
→ HEAD LICE treatment (5% lotion - Ulesfia brand)
→ Local anesthetic (mild)
→ Cosmetic solvent and fragrance fixative

---

🔑 BENZALDEHYDE — QUICK FACTS

Formula: C₆H₅CHO    MW: 106.12    BP: 178-179°C    Odor: Almond

PREPARATION:
1. Rosenmund: C₆H₅COCl + H₂ →[Pd/BaSO₄]→ C₆H₅CHO
2. Hydrolysis: C₆H₅CHCl₂ + H₂O →[Ca(OH)₂]→ C₆H₅CHO
3. Gattermann-Koch: C₆H₆ + CO + HCl →[AlCl₃/CuCl]→ C₆H₅CHO
4. Oxidation: C₆H₅CH₂OH →[MnO₂]→ C₆H₅CHO

PURITY TESTS:
✓ Refractive index: 1.544-1.546
✓ Benzoic acid test: NMT 0.05% (oxidizes on storage)
✓ Peroxide test: KI/acetic acid → no iodine liberation
✓ Assay: Hydroxylamine method (oxime formation, titration)
✓ Content: NLT 98.0% (IP)

MEDICINAL USES:
→ Flavoring agent (almond flavor in pharmaceuticals)
→ Intermediate for ampicillin synthesis
→ Intermediate for cinnamaldehyde synthesis
→ Perfumery and cosmetics

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🔑 CHLOROBUTANOL — QUICK FACTS

Formula: CCl₃C(CH₃)₂OH    MW: 177.46    MP: 95-98°C    Odor: Camphor

PREPARATION:
CHCl₃ + (CH₃)₂CO + KOH →[10-15°C]→ CCl₃-C(CH₃)₂-OH
(chloroform) (acetone)                (chlorobutanol)

Mechanism: KOH deprotonates CHCl₃ → :CCl₃⁻ → attacks acetone → alkoxide → 
           protonation → chlorobutanol

PURITY TESTS:
✓ MP: 97-100°C (anhydrous)
✓ Identification: + NaOH/heat + AgNO₃ → AgCl↓ (white ppt)
✓ Loss on drying: NMT 0.5% (anhydrous form)
✓ Chloroform odor on heating with H₂SO₄

ASSAY (ARGENTOMETRIC METHOD):
1. Saponify with NaOH (heat) → releases Cl⁻ ions
2. Titrate Cl⁻ with AgNO₃ (0.1M)
3. Indicator: K₂CrO₄ (brick-red endpoint = Mohr's method)
4. Formula: % purity = (titre × 0.1 × 59.15 × 100) / weight
   IP Specification: NLT 98.0%

MEDICINAL USES:
→ PRESERVATIVE (0.5%) - most important use
   (eye drops, ear drops, injectable preparations)
→ Mild sedative/CNS depressant (historical use)
→ Local anesthetic (mild)
→ Veterinary preservative

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⚡ ULTIMATE SPEED REVISION — REMEMBER THESE FIRST!

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╔═══════════════════════════════════════════════════════════════════╗
║              TOP 20 THINGS EXAMINERS LOVE TO ASK                 ║
╠═══════════════════════════════════════════════════════════════════╣
║ 1.  Lewis = electron pair (broadest acid-base theory)            ║
║ 2.  H-bond only with N, O, F (small + electronegative)           ║
║ 3.  Dipole moment: symmetric = zero (CO₂=0, H₂O=1.85D)          ║
║ 4.  Wohler 1828 = first organic synthesis (urea)                 ║
║ 5.  Alkane suffix = -ane; Alkene = -ene; Alkyne = -yne           ║
║ 6.  Aldehyde IUPAC = -al; Amine = -amine                        ║
║ 7.  SN2 = inversion; SN1 = racemization                          ║
║ 8.  SN2 = methyl/primary; SN1 = tertiary                         ║
║ 9.  Peroxide effect = ONLY HBr (both prop. steps exothermic)     ║
║ 10. Radical stability: Benzyl > Allyl > 3° > 2° > 1°             ║
║ 11. E2 requires anti-periplanar geometry (180°)                  ║
║ 12. Zaitsev = more substituted alkene; Hofmann = less (bulky)    ║
║ 13. Dehydration ease: 3° > 2° > 1° alcohol                      ║
║ 14. Cannizzaro = no α-H + conc NaOH → H⁻ transfer (NOT H⁺!)    ║
║ 15. Williamson = RONa + PRIMARY RX only → ether (SN2)            ║
║ 16. Fries: low T → para; high T → ortho                          ║
║ 17. Kolbe: Na-phenoxide → ortho; K-phenoxide → para              ║
║ 18. Reimer-Tiemann: CHCl₃ + NaOH → :CCl₂ → salicylaldehyde     ║
║ 19. Urea: Xanthydrol test (specific); 46.3-46.6% N (Kjeldahl)   ║
║ 20. Chlorobutanol assay: AgNO₃ titration (Mohr's method)         ║
╚═══════════════════════════════════════════════════════════════════╝

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╔═══════════════════════════════════════════════════════════════════╗
║           STABILITY ORDERS — ALL IN ONE PLACE                    ║
╠═══════════════════════════════════════════════════════════════════╣
║ CARBOCATIONS: Benzyl > Allyl > 3° > 2° > 1° > Methyl            ║
║ FREE RADICALS: Benzyl > Allyl > 3° > 2° > 1° > Methyl           ║
║ CARBANIONS: Methyl > 1° > 2° > 3° (OPPOSITE of above!)          ║
║ LEAVING GROUPS: TfO⁻ > TsO⁻ > I⁻ > Br⁻ > Cl⁻ >> F⁻ >> OH⁻    ║
║ NUCLEOPHILICITY (protic): I⁻ > Br⁻ > Cl⁻ > F⁻                  ║
║ RADICAL REACTIVITY: F• > Cl• > Br• > I•                         ║
║ RADICAL SELECTIVITY: I• > Br• > Cl• > F•                        ║
║ EAS REACTIVITY: Aniline >> Phenol > Toluene > Benzene > PhCl     ║
╚═══════════════════════════════════════════════════════════════════╝

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╔═══════════════════════════════════════════════════════════════════╗
║         NAMED REACTIONS — PRODUCT SUMMARY                        ║
╠═══════════════════════════════════════════════════════════════════╣
║ Williamson:     RONa + RX → R-O-R (ether)                        ║
║ Fries:          Phenyl ester → hydroxy aryl ketone               ║
║ Kolbe:          PhONa + CO₂ → salicylic acid                     ║
║ Reimer-Tiemann: PhOH + CHCl₃/NaOH → salicylaldehyde             ║
║ Cross Aldol:    ArCHO + CH₃CHO → cinnamaldehyde                  ║
║ Perkin:         ArCHO + anhydride → cinnamic acid                ║
║ Cannizzaro:     2ArCHO + NaOH → ArCH₂OH + ArCOONa               ║
║ Rosenmund:      RCOCl + H₂/Pd(BaSO₄) → RCHO                     ║
║ Gattermann-Koch: ArH + CO/HCl/AlCl₃ → ArCHO                     ║
╚═══════════════════════════════════════════════════════════════════╝

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🧪 ORGANIC CHEMISTRY — 2-MARK ANSWERS SUMMARY

All 80 Questions | Units 1–10 | Pharm D 1st Year | Super Simple Language

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▌UNIT 1 — BASICS OF ORGANIC CHEMISTRY

KEY FACTS — UNIT 1:
• Arrhenius = H⁺/OH⁻ in water only
• Bronsted = proton donor/acceptor
• Lewis = e⁻ pair donor/acceptor (BROADEST)
• H-bond only with N, O, F
• "Like dissolves like" (polarity rule)
• Dipole moment (μ) = q × d (unit = Debye)
• Symmetric molecule → μ = 0 (CO₂, CCl₄)

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▌UNIT 2 — CLASSIFICATION & NOMENCLATURE

KEY FACTS — UNIT 2:
• Alkane = -ane; Alkene = -ene; Alkyne = -yne
• Aldehyde IUPAC = -al (CHO at C-1)
• Amine IUPAC = -amine; secondary/tertiary = N-prefix
• Wohler (1828) disproved Vital Force Theory
• Aromatic = benzene ring + 4n+2 π electrons (Hückel rule)
• Conjugated diene = C=C-C=C (alternating)

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▌UNIT 3 — SN1, SN2, CARBOCATIONS

KEY FACTS — UNIT 3:
• SN2 = 1 step, inversion (Walden), polar APROTIC, primary substrate
• SN1 = 2 steps, racemization, polar PROTIC, tertiary substrate
• Good LG: TsO⁻ > I⁻ > Br⁻ > Cl⁻ >> F⁻ >> OH⁻
• Good Nu: OH⁻ > Cl⁻, strong bases, negative charge
• Steric: Methyl = open; 3° = totally blocked (only SN1)
• Carbocation rearranges to MORE STABLE cation (1,2-H or CH₃ shift)

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▌UNIT 4 — ELIMINATION REACTIONS

KEY FACTS — UNIT 4:
• E2 MUST have anti-periplanar H and LG (180° apart)
• Zaitsev = more substituted alkene MAJOR (small base)
• Hofmann = less substituted alkene MAJOR (bulky base like t-BuOK)
• High temperature FAVORS elimination over substitution
• Dehydration of 3°ROH easiest (most stable carbocation)
• E1 and SN1 COMPETE (same carbocation intermediate)

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▌UNIT 5 — ADDITION REACTIONS & MARKOVNIKOV

KEY FACTS — UNIT 5:
• Markovnikov = no peroxide = ionic = H⁺ adds first
• Anti-Markovnikov = peroxide/hν = radical = Br• adds first
• ONLY HBr shows peroxide effect (HCl and HI do NOT!)
• Reason: Both propagation steps must be exothermic → only HBr qualifies
• Radical stability: Benzyl > Allyl > 3° > 2° > 1° > Methyl
• Radical chain: very long (10,000+ cycles before termination)

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▌UNIT 6 — FREE RADICAL REACTIONS

KEY FACTS — UNIT 6:
• Conjugated diene + HBr → 1,2-addition (low T, kinetic) OR 1,4-addition (high T, thermodynamic)
• Allylic/benzylic C-H weakest → attacked first by radicals
• NBS = selective allylic bromination
• Resonance hybrid = actual structure (not individual resonance forms)
• Hyperconjugation: more C-H bonds adjacent = more stable (3° cation most stable)
• Free radical substitution = alkane substrate; addition = alkene substrate

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▌UNIT 7 — AROMATIC CHEMISTRY & EAS

KEY FACTS — UNIT 7:
• Halogens = DEACTIVATING (-I effect) but ORTHO/PARA directing (+M effect)
• This is the only unusual combination to remember!
• EAS mechanism: E⁺ attacks → arenium ion (sp3 carbon, not aromatic) → H⁺ leaves → re-aromatize
• Activating groups: -NH₂ > -OH > -OCH₃ > -CH₃
• Deactivating groups: -NO₂ > -CN > -COOH > halogens
• Benzyl radical: most stable (delocalized over 4 positions via resonance)
• BDE benzylic C-H = 85 kcal/mol (lowest = weakest = easiest to abstract)

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▌UNIT 8 — CARBONYL REACTIONS & CONDENSATIONS

KEY FACTS — UNIT 8:
• Aldol: requires α-H; dilute NaOH; gives β-hydroxy carbonyl → then dehydration
• Cross Aldol: use NO α-H compound (benzaldehyde) as electrophile for clean product
• Cannizzaro: NO α-H + CONC NaOH; H⁻ (hydride!) transfer is key step (NOT H⁺)
• Perkin: ArCHO + (RCH₂CO)₂O + RCH₂COONa → heat → cinnamic acid type product
• Benzoin: CN⁻ is both nucleophile AND leaving group (Umpolung concept)
• Wittig: converts C=O → C=C; stereospecific; used in drug synthesis
• Reformatsky: Zn inserts into C-Br bond of α-halo ester → organozinc → adds to C=O

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▌UNIT 9 — NAMED REACTIONS

KEY FACTS — UNIT 9:
• Williamson: RONa + PRIMARY RX → ether (SN2); NEVER use 3° RX (gives E2!)
• Fries: Low T → para; High T → ortho (remember: L-P, H-O)
• Kolbe: Na-phenoxide → ORTHO (salicylic acid); K-phenoxide → PARA
• Reimer-Tiemann: CHCl₃ + NaOH → :CCl₂ (carbene!) → formylation at ortho
• Sandmeyer: diazonium → ArCl, ArBr, ArCN, ArOH, ArF (all from N₂⁺)
• Diazotization: MUST be at 0-5°C (diazonium unstable at higher temperature)
• SNAr = addition-elimination via Meisenheimer complex intermediate

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▌UNIT 10 — PHARMACEUTICALS & ANALYTICAL

KEY FACTS — UNIT 10:

UREA:
• Preparation: NH₃ + CO₂ → urea (industrial); Wohler: NH₄CNO → urea
• Purity: MP 132-135°C | Xanthydrol test (specific!) | N content 46.3-46.6%
• Uses: Osmotic diuretic, keratolytic (10-40%), H. pylori breath test

BENZYL ALCOHOL:
• Preparation: Cannizzaro (from benzaldehyde) or hydrolysis of benzyl chloride
• Purity: RI = 1.539-1.541 | Peroxide test (KI) | Aldehyde test (Schiff's)
• Uses: Bacteriostatic preservative (0.9-1.5% in injections), head lice (5%)

BENZALDEHYDE:
• Preparation: Rosenmund reduction, hydrolysis of benzal chloride, Gattermann-Koch
• Purity: RI = 1.544-1.546 | Benzoic acid test | Hydroxylamine assay (NLT 98%)
• Uses: Almond flavoring agent, pharmaceutical intermediate (ampicillin)

CHLOROBUTANOL:
• Preparation: CHCl₃ + (CH₃)₂CO + KOH → CCl₃C(CH₃)₂OH
• Purity: MP 97-100°C | AgNO₃ test | Chloroform smell on heating
• Assay: Saponify with NaOH → Cl⁻ released → titrate with AgNO₃ (Mohr's method)
• Uses: Preservative 0.5% in eye drops, ear drops, injections

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╔═══════════════════════════════════════════════════════╗

║ MASTER CHEAT SHEET — ALL UNITS AT A GLANCE ║

╚═══════════════════════════════════════════════════════╝

STABILITY ORDERS (Most → Least Stable)

CARBOCATIONS:  Benzyl > Allyl > 3° > 2° > 1° > Methyl
FREE RADICALS: Benzyl > Allyl > 3° > 2° > 1° > Methyl
CARBANIONS:    Methyl > 1° > 2° > 3°  (OPPOSITE of above!)
LEAVING GROUP: I⁻ > Br⁻ > Cl⁻ >> F⁻ >> OH⁻
NUCLEOPHILE:   I⁻ > Br⁻ > Cl⁻ > F⁻ (protic solvent)
RADICAL REACTIVITY: F• > Cl• > Br• > I•
RADICAL SELECTIVITY: I• > Br• > Cl• > F•  (opposite of reactivity!)
EAS REACTIVITY: PhNH₂ >> PhOH > PhCH₃ > Ph-H > PhCl > PhNO₂

NAMED REACTIONS — PRODUCT IN ONE LINE

Aldol condensation → β-hydroxy carbonyl → dehydrate → enone
Cross Aldol        → cinnamaldehyde (ArCHO + CH₃CHO + NaOH)
Perkin             → cinnamic acid (ArCHO + anhydride + salt)
Cannizzaro         → acid salt + alcohol (no α-H + conc. NaOH)
Benzoin            → C₆H₅CH(OH)-CO-C₆H₅ (2 ArCHO + CN⁻)
Wittig             → alkene (C=O + ylide)
Reformatsky        → β-hydroxy ester (aldehyde + α-halo ester + Zn)
Williamson         → ether (RONa + primary RX, SN2)
Fries              → o-hydroxy ketone (high T) or p-hydroxy ketone (low T)
Kolbe              → salicylic acid (PhONa + CO₂, Na → ortho)
Reimer-Tiemann     → salicylaldehyde (PhOH + CHCl₃ + NaOH, :CCl₂ key!)
Sandmeyer          → ArCl/ArBr/ArCN (diazonium + Cu salt)
Diazotization      → diazonium salt (ArNH₂ + NaNO₂ + HCl, 0-5°C)
Rosenmund          → aldehyde (RCOCl + H₂/Pd-BaSO₄)
Gattermann-Koch    → benzaldehyde (ArH + CO + HCl + AlCl₃/CuCl)

EAS DIRECTORS — QUICK TABLE

ORTHO/PARA (activating):   -NH₂, -OH, -OR, -CH₃, alkyl groups
ORTHO/PARA (deactivating): -F, -Cl, -Br, -I  ← EXCEPTION! Know this!
META (deactivating):       -NO₂, -CN, -COOH, -CHO, -COR, -SO₃H

Rule: All deactivators are meta directors... EXCEPT HALOGENS!

SN1 vs SN2 vs E1 vs E2 — 4-WAY SUMMARY

Primary + strong Nu + polar aprotic  → SN2
Primary + strong bulky base          → E2 (Hofmann product)
Secondary + strong Nu + aprotic      → SN2
Secondary + strong base + heat       → E2 (Zaitsev product)
Tertiary + polar protic + weak Nu    → SN1 / E1 (compete)
Tertiary + strong base               → E2 only (no SN2 possible!)
Allylic/Benzylic + polar protic      → SN1' (rearranged product possible)

PHARMACEUTICAL QUICK FACTS

Compound      | MP/BP      | Key Test              | Main Use
──────────────────────────────────────────────────────────────
Urea          | 132-135°C  | Xanthydrol → white ppt | Keratolytic, diuretic
Benzyl alcohol| BP 205°C   | RI = 1.539-1.541       | Preservative, lice
Benzaldehyde  | BP 178°C   | RI = 1.544-1.546       | Flavoring, intermediate
Chlorobutanol | 97-100°C   | AgNO₃ after saponify   | Preservative 0.5%
Salicylic acid| 159°C      | FeCl₃ → violet color   | Keratolytic, aspirin

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⚡ LAST-MINUTE REVISION — TOP 25 FACTS

1.  Lewis theory = BROADEST (no proton needed)
2.  H-bond = ONLY N, O, F (small + very electronegative)
3.  Wohler 1828 = first organic synthesis (urea from NH₄CNO)
4.  SN2 = 1 step + inversion + primary substrate + polar APROTIC
5.  SN1 = 2 steps + racemization + tertiary + polar PROTIC
6.  E2 needs anti-periplanar geometry (H and LG at 180°)
7.  ONLY HBr shows peroxide effect (anti-Markovnikov)
8.  Radical stability: Benzyl > Allyl > 3° > 2° > 1°
9.  Halogens = DEACTIVATE ring BUT direct ORTHO/PARA
10. Carbocation rearranges toward MORE STABLE cation
11. Zaitsev = more substituted alkene (small base)
12. Hofmann = less substituted alkene (bulky base)
13. Cannizzaro key step = H⁻ HYDRIDE transfer (NOT H⁺!)
14. Perkin = ArCHO + anhydride → cinnamic acid type
15. Cross aldol = use benzaldehyde (no α-H) as acceptor
16. Williamson = MUST use primary RX (3° gives E2 only!)
17. Fries: LOW T → PARA; HIGH T → ORTHO
18. Kolbe: Na-phenoxide → ORTHO; K-phenoxide → PARA
19. Reimer-Tiemann: CHCl₃ + NaOH → :CCl₂ (carbene!) → salicylaldehyde
20. Urea test = Xanthydrol → dixanthyl urea (specific test)
21. Chlorobutanol assay = saponify → Cl⁻ → AgNO₃ titration (Mohr's)
22. Benzaldehyde oxidizes on storage → benzoic acid (test for it!)
23. Conjugated diene: Low T = 1,2-addition; High T = 1,4-addition
24. Good LG = weak base (I⁻ is BEST leaving group)
25. Allylic SN1' = Nu attacks either end of delocalized cation → 2 products

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