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🧪 ORGANIC CHEMISTRY — COMPLETE ANSWER GUIDE

University Level | 5 Marks Each | All 10 Units

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═══════════════════════════════════

UNIT 1 — ISOMERISM & BONDING

═══════════════════════════════════

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Q1. Chain Isomerism and Functional Isomerism

Chain Isomerism (Skeletal Isomerism)

CHAIN ISOMERISM DIAGRAM
────────────────────────────────────────────
Molecular Formula: C₅H₁₂

Isomer 1 — n-Pentane (straight chain):
    C—C—C—C—C
    
Isomer 2 — Isopentane (one branch):
        C
        |
    C—C—C—C
    
Isomer 3 — Neopentane (two branches):
          C
          |
      C—C—C
          |
          C
────────────────────────────────────────────
All three have formula C₅H₁₂ but DIFFERENT skeletons

• Butane (C₄H₁₀) → n-Butane and Isobutane
• Pentane (C₅H₁₂) → 3 isomers as above

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Functional Isomerism

FUNCTIONAL ISOMERISM TABLE
─────────────────────────────────────────────────────
Molecular Formula    Isomer A              Isomer B
─────────────────────────────────────────────────────
C₂H₆O              Ethanol               Dimethyl ether
                    (CH₃CH₂OH)            (CH₃-O-CH₃)
                    [Alcohol]             [Ether]
─────────────────────────────────────────────────────
C₃H₆O              Propanal              Acetone
                    (CH₃CH₂CHO)          (CH₃COCH₃)
                    [Aldehyde]            [Ketone]
─────────────────────────────────────────────────────
C₂H₄O₂             Acetic acid           Methyl formate
                    (CH₃COOH)            (HCOOCH₃)
                    [Carboxylic acid]     [Ester]
─────────────────────────────────────────────────────

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Q2. Polarity of Bond and Molecules

A) Polarity of a Bond (Bond Polarity)

BOND POLARITY DIAGRAM
───────────────────────────────────────────────────
Non-Polar Bond (equal sharing):
    H — H     (ΔEN = 0)
    δ⁰  δ⁰    No charge separation
    
Polar Bond (unequal sharing):
    H — Cl    (ΔEN = 1.0)
    δ⁺  δ⁻    Partial charges appear
    
    Arrow shows direction of electron pull:
    H ——→ Cl
    
Highly Polar / Ionic (ΔEN > 1.7):
    Na⁺  Cl⁻  (Full charge transfer)
───────────────────────────────────────────────────

• ΔEN = 0 → Non-polar covalent (e.g., H₂, Cl₂)
• ΔEN = 0.1 to 1.7 → Polar covalent (e.g., H₂O, HCl, C-O, C-N)
• ΔEN > 1.7 → Ionic bond

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B) Polarity of a Molecule

MOLECULAR POLARITY DIAGRAM
──────────────────────────────────────────────────────
CO₂ — NON-POLAR MOLECULE (Linear, dipoles cancel):
        O ←— C —→ O
        (dipoles point opposite, cancel out)
        Net dipole = 0
        
H₂O — POLAR MOLECULE (Bent, dipoles don't cancel):
          O
         / \
        H   H
        (105° bend, dipoles add up)
        Net dipole ≠ 0, points toward O
        
CHCl₃ — POLAR (Asymmetric arrangement of Cl):
        Net dipole toward Cl side
        
CCl₄ — NON-POLAR (Tetrahedral, all Cl cancel out)
──────────────────────────────────────────────────────

1. Electronegativity difference between atoms
2. Shape/geometry of molecule
3. Lone pairs (distort geometry → polarity)

• μ = q × d (charge × distance)
• Unit: Debye (D)
• Higher μ = more polar molecule

• Polar molecules dissolve in polar solvents ("like dissolves like")
• Non-polar molecules dissolve in non-polar solvents
• Polarity affects boiling point, melting point, solubility

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Q3. Stereoisomerism in Detail

CLASSIFICATION OF STEREOISOMERISM
─────────────────────────────────────────────────
           STEREOISOMERISM
                 |
    ┌────────────┴──────────────┐
    │                          │
GEOMETRIC                  OPTICAL
(Cis-Trans)               (Mirror Images)
    │                          │
    ├── Cis isomer         ├── Enantiomers
    └── Trans isomer       └── Diastereomers
─────────────────────────────────────────────────

A) Geometric (Cis-Trans) Isomerism

2-Butene — C₄H₈

Cis-2-butene:            Trans-2-butene:
  CH₃   CH₃               CH₃   H
    \   /                    \  /
     C=C                      C=C
    /   \                    /   \
   H     H                  H   CH₃
  
(Same groups on SAME side)  (Same groups on OPPOSITE sides)

• Cis and trans isomers have different physical properties (bp, mp, density)
• Cis isomers are more polar (same groups on same side)

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B) Optical Isomerism (Chirality)

• Optical isomers rotate plane-polarized light
• Enantiomers are non-superimposable mirror images
• Full details in Q4 below

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C) Conformational Isomerism

Newman Projection of Ethane:
Staggered (more stable):    Eclipsed (less stable):
      H                           H
   H/ | \H                    H/ | \H
    —— | ——                    —— | ——
   H\ | /H                    H\ | /H
      H                           H
(60° between H atoms)       (0° — H atoms aligned)

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Summary Table:

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Q4. Optical Isomerism — Detailed Note

Definition

Key Terms

KEY CONCEPTS IN OPTICAL ISOMERISM
─────────────────────────────────────────────────────
1. CHIRAL CARBON (Asymmetric Carbon):
   A carbon bonded to 4 DIFFERENT groups
   Example: Lactic acid
   
         COOH
          |
   CH₃ — C* — OH    (* = chiral carbon)
          |
          H
          
2. CHIRALITY: Property of being non-superimposable
   on its mirror image (like hands — left ≠ right)

3. ENANTIOMERS: A pair of non-superimposable 
   mirror image isomers
   
4. RACEMIC MIXTURE: 50:50 mix of both enantiomers
   → Net optical rotation = 0 (optically inactive)

5. DIASTEREOMERS: Stereoisomers that are NOT
   mirror images of each other
─────────────────────────────────────────────────────

Mirror Image Diagram of Lactic Acid:

        COOH                    COOH
         |                        |
  H  — C* — OH       HO — C* — H
         |                        |
        CH₃                     CH₃
        
  D-Lactic acid          L-Lactic acid
  (dextrorotatory +)     (levorotatory −)
  
  These are ENANTIOMERS
  ←—— Mirror Plane ——→

Optical Activity

• Dextrorotatory (+): Rotates light clockwise (to the right)
• Levorotatory (-): Rotates light counterclockwise (to the left)
• Measured using a polarimeter

R and S Configuration (CIP Rules):

ASSIGNING R/S CONFIGURATION:
Step 1: Assign priority (1→4) based on atomic number
        Higher atomic number = higher priority
Step 2: Arrange molecule with lowest priority (4) 
        pointing AWAY from you
Step 3: Trace 1→2→3 direction:
        Clockwise = R (Rectus = right)
        Counter-clockwise = S (Sinister = left)

Meso Compounds

Meso-Tartaric Acid:
    COOH
     |
H — C — OH
     |
HO— C — H     ← internal mirror plane between the two carbons
     |
    COOH
    
(Has 2 chiral carbons but is optically inactive)

Summary:

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Q5. Position Isomerism and Tautomerism

A) Position Isomerism

POSITION ISOMERISM EXAMPLES
──────────────────────────────────────────────────
Example 1: Propanol (C₃H₇OH)

1-Propanol:               2-Propanol:
CH₃-CH₂-CH₂-OH           CH₃-CH(OH)-CH₃
(OH at carbon 1)          (OH at carbon 2)

Example 2: Dichlorobenzene (C₆H₄Cl₂)

Ortho (1,2):   Cl and Cl on adjacent carbons
Meta  (1,3):   Cl and Cl with one carbon between
Para  (1,4):   Cl and Cl on opposite carbons

     Cl            Cl           Cl
      \             \             |
  [ring]        [ring]        [ring]
      /              \             |
    Cl              Cl           Cl
  ortho (o-)     meta (m-)    para (p-)
──────────────────────────────────────────────────

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B) Tautomerism

KETO-ENOL TAUTOMERISM
──────────────────────────────────────────────────
         O                        OH
         ‖                         |
CH₃ — C — CH₃    ⇌    CH₃ — C = CH₂
      
   Keto form                  Enol form
  (more stable,              (less stable,
   predominates)              minor form)
   
        ⇌ (equilibrium arrow)
──────────────────────────────────────────────────
Mechanism:
  - A proton (H) migrates from α-carbon to oxygen
  - Double bond shifts from C=O to C=C
  - Catalyzed by acid or base
──────────────────────────────────────────────────

1. Ring-chain tautomerism (e.g., glucose open chain ⇌ cyclic form)
2. Valence tautomerism (involves bond breaking/forming)
3. Prototropic tautomerism (proton shift — like keto-enol)

• Isomers exist as separate stable compounds
• Tautomers exist in dynamic equilibrium and interconvert rapidly

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Q6. Arrhenius Theory and its Limitations

Arrhenius Theory of Acids and Bases (1884)

ARRHENIUS THEORY — EQUATIONS
─────────────────────────────────────────────────────
ACIDS (produce H⁺):
    HCl      → H⁺  +  Cl⁻
    H₂SO₄   → 2H⁺ + SO₄²⁻
    HNO₃    → H⁺  + NO₃⁻

BASES (produce OH⁻):
    NaOH    → Na⁺  + OH⁻
    KOH     → K⁺   + OH⁻
    Ca(OH)₂ → Ca²⁺ + 2OH⁻

NEUTRALIZATION:
    Acid + Base → Salt + Water
    HCl + NaOH → NaCl + H₂O
    H⁺ + OH⁻   → H₂O
─────────────────────────────────────────────────────

Arrhenius Equation (Rate-Temperature Relationship)

k = A · e^(-Ea/RT)

Where:
  k  = rate constant
  A  = frequency factor (pre-exponential factor)
  Ea = activation energy (J/mol)
  R  = gas constant (8.314 J/mol·K)
  T  = temperature in Kelvin

Log form:
  log k = log A − (Ea / 2.303RT)
  
  Plotting log k vs 1/T gives a straight line:
  Slope = −Ea/2.303R

Limitations of Arrhenius Theory

LIMITATIONS TABLE
─────────────────────────────────────────────────────────────
# | Limitation            | Explanation
─────────────────────────────────────────────────────────────
1 | Only for water         | Cannot explain acids/bases in
  | (aqueous solutions)   | non-aqueous solvents like
  |                       | liquid ammonia, benzene, etc.
─────────────────────────────────────────────────────────────
2 | Cannot explain NH₃    | NH₃ is a base but produces NO
  | as a base             | OH⁻ — it accepts H⁺ instead
─────────────────────────────────────────────────────────────
3 | Cannot explain CO₂,   | CO₂ is acidic in water but
  | SO₂ as acids          | produces H⁺ only indirectly
  |                       | (CO₂ + H₂O → H₂CO₃)
─────────────────────────────────────────────────────────────
4 | Fails for aprotic     | Substances like AlCl₃ act as
  | Lewis acids           | acids without producing H⁺
─────────────────────────────────────────────────────────────
5 | No explanation for    | Cannot define proton donors/
  | proton transfer       | acceptors in a generalized way
─────────────────────────────────────────────────────────────
6 | Incomplete picture    | Superseded by Bronsted-Lowry
  |                       | and Lewis theories
─────────────────────────────────────────────────────────────

• Bronsted-Lowry Theory: Acid = proton donor; Base = proton acceptor (works in non-aqueous too)
• Lewis Theory: Acid = electron pair acceptor; Base = electron pair donor (most general)

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═══════════════════════════════════

UNIT 2 — FREE RADICALS & NAMING

═══════════════════════════════════

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Q1. Stability of Free Radicals

Stability Order:

STABILITY ORDER OF FREE RADICALS
─────────────────────────────────────────────────────
Tertiary > Secondary > Primary > Methyl

    3°        >     2°     >    1°    >    CH₃•
(Most stable)                        (Least stable)

WHY?
→ More alkyl groups attached = more hyperconjugation
→ More electron donation into the radical center
→ Greater delocalization of unpaired electron
─────────────────────────────────────────────────────

Structure:

Methyl radical (least stable):
        •
    H — C — H
        |
        H

Primary radical:
        •
    R — C — H
        |
        H

Tertiary radical (most stable):
        •
    R — C — R
        |
        R

Factors Affecting Stability:

Special Cases (Extra stable):

Allylic radical:
    CH₂=CH—CH₂•  ←→  •CH₂—CH=CH₂
    (Resonance stabilization)
    
Benzylic radical:
    Ph—CH₂•  (delocalized into benzene ring)
    (Most stable carbon radical)

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Q2. Naming Rules for Alkyl Halides

IUPAC Naming Rules:

STEP-BY-STEP NAMING OF ALKYL HALIDES
─────────────────────────────────────────────────────
Step 1: Find the longest carbon chain containing the
        halogen → this is the parent chain.

Step 2: Number the chain from the END nearest to 
        the halogen to give it the LOWEST number.

Step 3: Name the halogen as a prefix:
        F = Fluoro-
        Cl = Chloro-
        Br = Bromo-
        I = Iodo-

Step 4: Name the parent chain (alkane name).

Step 5: Write: Position-halo + parent chain name
─────────────────────────────────────────────────────

Examples:

EXAMPLES TABLE
─────────────────────────────────────────────────────
Structure              IUPAC Name
─────────────────────────────────────────────────────
CH₃Cl                  Chloromethane
CH₃CH₂Br               1-Bromoethane
CH₃CHClCH₃             2-Chloropropane
CH₃CH₂CH₂I             1-Iodopropane
CH₃CHBrCH₂CH₃          2-Bromobutane
(CH₃)₃CCl              2-Chloro-2-methylpropane
CH₂Cl₂                  Dichloromethane
CHCl₃                   Trichloromethane (Chloroform)
CCl₄                    Tetrachloromethane
─────────────────────────────────────────────────────

Classification:

1° (Primary): Halogen on a carbon bonded to 1 alkyl group
    e.g., CH₃CH₂Cl

2° (Secondary): Halogen on carbon bonded to 2 alkyl groups
    e.g., (CH₃)₂CHBr

3° (Tertiary): Halogen on carbon bonded to 3 alkyl groups
    e.g., (CH₃)₃CCl

---

Q3. Free Radicals — Definition and Mechanism

Definition

FORMATION OF FREE RADICALS
─────────────────────────────────────────────────────
Homolytic Cleavage:
    A : B  ──light/heat──→  A•  +  B•
    
Each atom gets ONE electron from the shared pair.

Example:
    Cl—Cl  ──hν──→  Cl•  +  Cl•
    (chlorine radical)
─────────────────────────────────────────────────────

Mechanism of Free Radical Halogenation (e.g., Chlorination of Methane)

FREE RADICAL CHAIN MECHANISM
─────────────────────────────────────────────────────
REACTION: CH₄ + Cl₂ → CH₃Cl + HCl (in light/hν)

STEP 1 — INITIATION:
    Cl₂  ──hν──→  Cl• + Cl•
    (UV light breaks Cl-Cl bond homolytically)

STEP 2 — PROPAGATION (chain-carrying steps):
    Cl• + CH₄  →  HCl  +  CH₃•   (H abstraction)
    CH₃• + Cl₂ →  CH₃Cl + Cl•   (Cl abstraction)
    
    (Cl• is regenerated → chain continues)

STEP 3 — TERMINATION (chain-ending steps):
    Cl•  + Cl•  → Cl₂
    CH₃• + CH₃• → C₂H₆
    CH₃• + Cl•  → CH₃Cl
─────────────────────────────────────────────────────

Energy Profile:

Energy
  |           Transition State
  |          /\   /\
  |         /  \ /  \
  |        /    V    \
  |       /  Products \
  | Reactants          \
  |____________________________→ Reaction coordinate

• Very short-lived (microseconds)
• Very reactive
• Can be detected by ESR (Electron Spin Resonance)
• Involved in combustion, polymerization, atmospheric reactions

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Q4. Naming Rules for Carboxylic Acids

IUPAC Naming Rules:

STEP-BY-STEP NAMING
─────────────────────────────────────────────────────
Step 1: Find the longest chain INCLUDING the 
        carboxyl carbon (C=O and O-H carbon).

Step 2: The carboxyl carbon is ALWAYS carbon #1.
        (Always gets the lowest number)

Step 3: Drop "-e" from alkane name, add "-oic acid"

Step 4: Number substituents, name them as prefixes.
─────────────────────────────────────────────────────

Examples:

COMMON CARBOXYLIC ACIDS
─────────────────────────────────────────────────────
Structure                 IUPAC Name      Common Name
─────────────────────────────────────────────────────
HCOOH                    Methanoic acid   Formic acid
CH₃COOH                  Ethanoic acid    Acetic acid
CH₃CH₂COOH               Propanoic acid   Propionic acid
CH₃CH₂CH₂COOH            Butanoic acid    Butyric acid
(CH₃)₂CHCOOH              2-Methylpropanoic acid  Isobutyric
HOOCCOOH                  Ethanedioic acid  Oxalic acid
HOOCCH₂COOH               Propanedioic acid  Malonic acid
CH₃CH(OH)COOH             2-Hydroxypropanoic acid  Lactic acid
─────────────────────────────────────────────────────

Dicarboxylic Acids:

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Q5. Naming Rules for Amides

IUPAC Naming Rules:

STEP-BY-STEP NAMING OF AMIDES
─────────────────────────────────────────────────────
Step 1: Find the parent carboxylic acid name.

Step 2: Replace "-oic acid" with "-amide"
        (OR replace "-ic acid" with "-amide")

Step 3: If N has substituents (N-alkyl amides):
        Use N- prefix for groups on nitrogen

Step 4: For cyclic amides (lactams):
        Use "-lactam" naming
─────────────────────────────────────────────────────

Examples:

AMIDE NAMING EXAMPLES
─────────────────────────────────────────────────────
Structure                   IUPAC Name
─────────────────────────────────────────────────────
HCONH₂                      Methanamide (Formamide)
CH₃CONH₂                    Ethanamide (Acetamide)
CH₃CH₂CONH₂                 Propanamide
CH₃CON(CH₃)₂                N,N-Dimethylethanamide
CH₃CONHCH₃                  N-Methylethanamide
C₆H₅CONH₂                   Benzamide
─────────────────────────────────────────────────────

Structure:

Primary amide:         Secondary amide:      Tertiary amide:
    O                      O                     O
    ‖                      ‖                     ‖
R — C — NH₂            R — C — NH — R'       R — C — N(R')₂

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Q6. Relative Stability of Free Radicals

Summary Table:

RELATIVE STABILITY (Decreasing order)
─────────────────────────────────────────────────────
Benzylic > Allylic > 3° > 2° > 1° > Methyl•
(Most stable)                      (Least stable)
─────────────────────────────────────────────────────

Bond Dissociation Energies (BDE):

Higher BDE = harder to form radical = less stable radical
Lower BDE  = easier to form radical = more stable radical

Type           BDE (approx.)       Stability
─────────────────────────────────
Methyl C-H    ~439 kJ/mol         Least stable
1° C-H        ~422 kJ/mol
2° C-H        ~413 kJ/mol
3° C-H        ~400 kJ/mol
Allylic C-H   ~369 kJ/mol
Benzylic C-H  ~356 kJ/mol         Most stable

Why Benzylic is Most Stable:

Ph-CH₂•  resonance structures:

   [Ph]—CH₂•  ←→  [•Ph]—CH₂
   
The unpaired electron is delocalized over the 
entire benzene ring through resonance.

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═══════════════════════════════════

UNIT 3 — SUBSTITUTION REACTIONS

═══════════════════════════════════

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Q1. Stereochemistry of SN2 Reaction

Definition

• One step reaction
• Backside attack by nucleophile
• Inversion of configuration (Walden Inversion)

Mechanism:

SN2 MECHANISM — BACKSIDE ATTACK
──────────────────────────────────────────────────────
                Nu:⁻ attacks from BACK side

     Nu:⁻  +   C — LG   →   Nu — C   +  LG⁻

Starting material:      Transition State:         Product:
    R₁                      R₁                     R₁
    |                  Nu--C--LG                    |
Nu: → C — LG   →      (pentavalent)    →   Nu — C
    |                      |                       |
    R₂                     R₂                      R₂
    R₃                     R₃                      R₃

Where LG = Leaving Group
──────────────────────────────────────────────────────

Walden Inversion (Stereochemical Outcome):

Backside attack INVERTS configuration
(Like an umbrella turning inside out in wind)

   R₁                             R₁
    \                               \
Nu: → C — LG    →        Nu — C
    /                               /
   R₂                             R₂
   R₃                             R₃

If starting material is R-configuration,
product will be S-configuration (and vice versa)
= 100% INVERSION

Key Features of SN2:

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Q2. Kinetics of First and Second Order Reactions

First Order Reaction

FIRST ORDER REACTION
─────────────────────────────────────────────────────
Rate Law:
    Rate = k[A]

Differential form:
    -d[A]/dt = k[A]

Integrated form:
    ln[A] = ln[A]₀ - kt
    OR
    [A] = [A]₀ · e^(-kt)

Half-life (t₁/₂):
    t₁/₂ = 0.693/k  (independent of initial concentration)

Graph: Plot of ln[A] vs time → STRAIGHT LINE (slope = -k)

Example: Radioactive decay, SN1 reaction, 
         decomposition of N₂O₅
─────────────────────────────────────────────────────

Second Order Reaction

SECOND ORDER REACTION
─────────────────────────────────────────────────────
Rate Law (Type 1):
    Rate = k[A]²

Rate Law (Type 2):
    Rate = k[A][B]

Integrated form (for [A]²):
    1/[A] = 1/[A]₀ + kt

Half-life:
    t₁/₂ = 1/(k[A]₀)  (depends on initial concentration)

Graph: Plot of 1/[A] vs time → STRAIGHT LINE (slope = +k)

Example: SN2 reaction, H₂ + I₂ → 2HI
─────────────────────────────────────────────────────

Comparison Table:

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Q3. Rearrangement of Carbocation

Types of Rearrangements:

1. HYDRIDE SHIFT (1,2-H shift)
──────────────────────────────────────────────────────
A hydrogen with its bonding electrons migrates from 
an adjacent carbon to the carbocation.

Example:
    +
CH₃-CH-CH₂-CH₃  →  CH₃-CH₂-CH⁺-CH₃
(1° carbocation)     (2° carbocation — more stable)
        ↑ H migrates with electrons

2. METHYL/ALKYL SHIFT (1,2-alkyl shift)
──────────────────────────────────────────────────────
An alkyl group migrates to the adjacent carbocation.

Example:
    +               
CH₃-C-CH₂-CH₃  →  CH₃-C⁺-CH₂-CH₃  →  (CH₃)₂C⁺-CH₃
    |                   |
   CH₃                 CH₃
(2° becomes 3° after methyl shift)

Driving Force:

Example in Dehydration:

Neopentanol dehydration — expected vs actual product:

(CH₃)₃C-CH₂-OH  →  (CH₃)₃C-CH₂⁺  →  methyl shift  
→  (CH₃)₂C⁺-CH₂CH₃  →  (CH₃)₂C=CHCH₃  (actual product)
                         (2-methylbut-2-ene)

---

Q4. Role of Solvent in SN1 Reaction

SN1 = Substitution, Nucleophilic, Unimolecular

SN1 MECHANISM (2 steps):

Step 1 (SLOW — Rate Determining):
    R-LG  →  R⁺  +  LG⁻
    (Ionization — forms carbocation)

Step 2 (FAST):
    R⁺  +  Nu:⁻  →  R-Nu
    (Nucleophile attacks carbocation)

Rate = k[R-LG]  (only substrate, not nucleophile)

Role of Solvent in SN1:

POLAR PROTIC SOLVENTS ARE BEST FOR SN1
─────────────────────────────────────────────────────────
Polar Protic Solvents: water (H₂O), ethanol (EtOH),
                        acetic acid, methanol, etc.

WHY POLAR PROTIC SOLVENTS HELP SN1:

1. SOLVATION OF LEAVING GROUP:
   Solvent molecules surround and stabilize the LG⁻
   through hydrogen bonding
   → makes ionization easier → faster rate

2. SOLVATION OF CARBOCATION:
   Polar solvent stabilizes the R⁺ intermediate
   through ion-dipole interactions
   → carbocation is more stable → reaction faster

3. DIELECTRIC CONSTANT:
   High dielectric constant solvents (water = 80)
   reduce electrostatic attraction between ions
   → promotes ionization

EFFECT ON RATE:
   Increasing solvent polarity → INCREASES SN1 rate

EFFECT ON STEREOCHEMISTRY:
   In SN1, nucleophile attacks from BOTH faces of
   the planar carbocation:
   → Gives RACEMIC MIXTURE (50:50 R and S)
─────────────────────────────────────────────────────────

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Q5. Phase Transfer Catalysis (PTC)

Problem it Solves:

PHASE TRANSFER CATALYSIS — MECHANISM
─────────────────────────────────────────────────────────
           ORGANIC PHASE (non-polar)
         ─────────────────────────────
              Q⁺X⁻ → Q⁺Y⁻
         ─────────────────────────────
           AQUEOUS PHASE (polar)
         ─────────────────────────────
              Q⁺Y⁻ → Q⁺X⁻

Where:
  Q⁺ = Phase transfer catalyst (quaternary ammonium ion)
  X⁻ = Nucleophile (e.g., CN⁻, OH⁻)
  Y⁻ = Product anion (leaving group)
─────────────────────────────────────────────────────────
Step 1: Q⁺X⁻ (catalyst + nucleophile pair) enters 
        organic phase
Step 2: Reaction occurs: R-Y + Q⁺X⁻ → R-X + Q⁺Y⁻
Step 3: Q⁺Y⁻ moves back to aqueous phase
Step 4: Q⁺ picks up new X⁻, cycle repeats

• Tetrabutylammonium bromide (TBAB)
• Benzyltriethylammonium chloride (TEBA)
• Crown ethers (complex cations)

• Avoids expensive polar aprotic solvents
• Faster reactions at milder temperatures
• Environmentally friendly (less solvent needed)

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Q6. Baeyer Strain Theory and Angle Strain

Baeyer Strain Theory (1885)

BAEYER STRAIN THEORY
─────────────────────────────────────────────────────────
Ideal C-C-C bond angle = 109.5° (tetrahedral, sp³)

For a regular polygon of n sides:
Interior angle = 180° × (n-2) / n

Strain per carbon = (109.5° - actual ring angle) / 2

Ring    Sides  Interior   Deviation     Strain
        (n)    Angle      from 109.5°
─────────────────────────────────────────────────────────
Cyclopropane  3    60°      -49.5°/2 = 24.75°  Very high
Cyclobutane   4    90°      -19.5°/2 = 9.75°   High
Cyclopentane  5   108°       +1.5°/2 = 0.75°   Very low
Cyclohexane   6   120°      -10.5°/2 = 5.25°*  
Cycloheptane  7   128.6°    +19.1°/2 = 9.55°   High
─────────────────────────────────────────────────────────
*Cyclohexane has very low strain due to chair conformation

Orbital Overlap / Angle Strain:

CYCLOPROPANE — MAXIMUM STRAIN:
    Normal C-C bond: head-on sigma overlap (180°)
    
    In cyclopropane:
    Bond angle = 60° (forced)
    Orbitals can't overlap head-on → "bent bonds"
    (banana bonds)
    
    H₂C ——— CH₂
        \   /
         CH₂
        (60°)
    
    This poor overlap = high energy = high strain
    = RING STRAIN (ANGLE STRAIN)

Types of Strain in Cyclic Molecules:

Chair Conformation of Cyclohexane:

Cyclohexane relieves ALL strain in chair conformation:
  - Bond angles ≈ 111° (close to 109.5°)
  - Staggered arrangement (no torsional strain)
  - Substituents can be equatorial (less steric strain)
  
  Chair:           Boat (strained):
    /\/\              /\__/\
   /    \            /      \
  (stable)          (less stable)

---

═══════════════════════════════════

UNIT 4 — ELIMINATION REACTIONS (E1 & E2)

═══════════════════════════════════

---

Q1. Mechanism of E1 Reaction

Definition:

Mechanism:

E1 MECHANISM — 2 STEPS
──────────────────────────────────────────────────────
Example: (CH₃)₃CBr  →  (CH₃)₂C=CH₂  +  HBr

STEP 1 — IONIZATION (SLOW — Rate Determining):
    (CH₃)₃C—Br  →  (CH₃)₃C⁺  +  Br⁻
    
    Substrate loses leaving group to form carbocation
    Rate = k[(CH₃)₃CBr]

STEP 2 — DEPROTONATION (FAST):
    (CH₃)₃C⁺  +  Base:  →  (CH₃)₂C=CH₂  +  H-Base⁺
    
    Base removes a β-proton (H from adjacent carbon)
    Pi bond forms, alkene is produced
──────────────────────────────────────────────────────

Energy Diagram:

Energy
  |      TS1
  |     /  \    TS2
  |    /    \  /   \
  |   /   Carbocation
  |  /    intermediate
  | /              \
  |/                \
  Reactant        Product
  
  (Two energy humps = 2 transition states = 2 steps)

Key Features of E1:

Regioselectivity (Zaitsev's Rule):

(CH₃)₃C⁺  —  CH₂-CH₃  →  (CH₃)₂C=CH-CH₃  (major, Zaitsev)
                            vs CH₂=C(CH₃)₂  (minor)

---

Q2. Mechanism of E2 Reaction

Definition:

Mechanism:

E2 MECHANISM — CONCERTED (1 STEP)
──────────────────────────────────────────────────────
Base removes β-H AND leaving group leaves SIMULTANEOUSLY

          H   LG
          |   |          
Base:⁻——H—Cβ—Cα—  →  Base-H  +  C=C  +  LG⁻
             
All 3 events happen at the SAME TIME:
1. B: abstracts H from β-carbon
2. Pi bond (C=C) forms
3. Leaving group (LG) departs

RATE = k[substrate][base]  (2nd order)
──────────────────────────────────────────────────────

Stereospecificity — Anti-Periplanar Requirement:

ANTI-PERIPLANAR GEOMETRY REQUIRED:

Newman Projection:
       H (β)
       |
  R₁ — Cβ — R₂
       |
      Cα
     / | \
   LG  H  R₃

For E2, the H (β) and LG must be ANTI (180°) to each other:

      H
      |
  ——Cβ——
      |
  ——Cα——
      |
     LG  ← H and LG must be trans/anti

This gives a TRANS alkene preferentially (anti elimination)

Stereochemical Outcome:

Anti-elimination → Trans alkene (major product)

meso-2,3-Dibromobutane + 2Br⁻:
    → Only trans-2-butene (anti-periplanar eliminated)

(2R,3R)-2,3-Dibromobutane:
    → Only cis-2-butene

---

Q3. Absence of Rearrangement and Isotope Effect

A) Absence of Rearrangement in E2:

E1 (rearrangement possible):
  R—LG  →  R⁺  →  R'⁺ (rearranged)  →  alkene

E2 (no rearrangement):
  Base + R—LG  →  alkene in ONE step (no R⁺ intermediate)

B) Isotope Effect:

ISOTOPE EFFECT IN E2:

Normal E2:    k_H  (rate with C-H bond breaking)
Deuterated:   k_D  (rate with C-D bond breaking)

k_H / k_D = 2-7 (large primary KIE)
This proves C-H bond breaks in the rate-determining step

IN E1:
  k_H / k_D ≈ 1 (no isotope effect on rate)
  (C-H bond breaks AFTER the RDS = ionization step)
  
Therefore:
  Large KIE → E2 mechanism (C-H breaks in RDS)
  No KIE   → E1 mechanism (C-H breaks after RDS)

---

Q4. Dehydration of Alcohols

Mechanism:

DEHYDRATION OF ALCOHOLS (ACID CATALYZED — E1 type)
──────────────────────────────────────────────────────
Example: Ethanol → Ethylene + Water
         CH₃CH₂OH  →  CH₂=CH₂  +  H₂O

STEP 1 — PROTONATION OF OH:
    CH₃CH₂-OH + H⁺  →  CH₃CH₂-OH₂⁺
    (O becomes protonated → good leaving group)

STEP 2 — IONIZATION (Loss of water):
    CH₃CH₂-OH₂⁺  →  CH₃CH₂⁺  +  H₂O
    (Carbocation forms — SLOW step)

STEP 3 — DEPROTONATION:
    CH₃CH₂⁺  +  H₂O  →  CH₂=CH₂  +  H₃O⁺
    (Base removes β-H, double bond forms)
──────────────────────────────────────────────────────

Order of Reactivity (Ease of Dehydration):

3° alcohol > 2° alcohol > 1° alcohol

(Easier to form more stable carbocation)

Zaitsev's Rule in Dehydration:

2-Methylbutan-2-ol dehydration:
    
    CH₃                CH₃
    |       H₂SO₄      |
CH₃-C-CH₂CH₃  →  CH₃-C=CHCH₃  (major — more substituted)
    |  Δ              
    OH
                  + CH₂=C(CH₃)-CH₂CH₃  (minor)

---

Q5. Elimination via Carbocation (E1 Pathway)

E1 ELIMINATION VIA CARBOCATION
──────────────────────────────────────────────────────
Conditions: Polar protic solvent, weak base, heat, 
            tertiary/secondary substrate

R₃C-LG   →[slow, rate-determining]→   R₃C⁺  +  LG⁻
                                        
                                       ↓ (fast)
                                    
                                    Base removes β-H
                                    
                                   →  R₂C=CH₂  +  H-Base
──────────────────────────────────────────────────────

1. Allows rearrangement (hydride/alkyl shifts)
2. Gives racemic or mixed stereochemistry products
3. Competes with SN1 (same intermediate)
4. Favored by tertiary substrates (most stable carbocation)

---

Q6. Evidence for E2 Mechanism

EVIDENCE FOR E2 (CONCERTED) MECHANISM
─────────────────────────────────────────────────────────────
Evidence 1: SECOND ORDER KINETICS
→ Rate = k[substrate][base]
→ Base is involved in the rate-determining step
→ Contradicts E1 (where only substrate matters)

Evidence 2: KINETIC ISOTOPE EFFECT (KIE)
→ k_H/k_D = 2-7 (large primary KIE)
→ Proves C-H bond is broken in the RDS
→ In E1, no KIE because C-H breaks after RDS

Evidence 3: ANTI-PERIPLANAR STEREOSPECIFICITY
→ Only anti-elimination products are formed
→ meso-stilbene dibromide → only trans-stilbene
→ This strict geometry requirement proves ONE-STEP
→ Two-step (E1) would give both cis and trans

Evidence 4: NO REARRANGEMENT
→ No carbocation forms → no rearrangement
→ E1 shows rearrangements → evidence against carbocation
→ E2 products are NEVER rearranged

Evidence 5: EFFECT OF BASE CONCENTRATION
→ Increasing [base] → increases E2 rate
→ E1 rate is independent of [base]
→ Proves base participates in RDS
─────────────────────────────────────────────────────────────

---

═══════════════════════════════════

UNIT 5 — ADDITION REACTIONS

═══════════════════════════════════

---

Q1. Mechanism of Free Radical Addition

Overall Reaction:

Mechanism:

FREE RADICAL ADDITION MECHANISM (Peroxide initiated)
──────────────────────────────────────────────────────
STEP 1 — INITIATION:
    Peroxide (ROOR)  →[hν or Δ]→  2 RO•
    RO• + HBr  →  ROH + Br•
    (Bromine radical formed)

STEP 2 — PROPAGATION:
    Br• + CH₂=CH₂  →  BrCH₂-CH₂•    (Br adds to less substituted C)
    BrCH₂-CH₂• + HBr  →  BrCH₂-CH₃ + Br•
    
    (Br• regenerated → chain continues)

STEP 3 — TERMINATION:
    Br• + Br•  →  Br₂
    R• + Br•   →  R-Br
    R• + R•    →  R-R
──────────────────────────────────────────────────────

Anti-Markovnikov Addition:

• In ionic addition: Br goes to MORE substituted carbon (Markovnikov)
• In FREE RADICAL addition: Br goes to LESS substituted carbon (anti-Markovnikov)
• This is due to stability of the radical intermediate

    Br• + CH₂=CHCH₃   →   BrCH₂-CH•-CH₃  (2° radical — MAJOR)
                       →   BrCH(•)-CH₂CH₃  (1° radical — minor)
    
    More stable radical forms → Anti-Markovnikov product

---

Q2. Mechanism of Halogenation of Alkenes

Electrophilic Addition Mechanism:

HALOGENATION OF ALKENES (Electrophilic Addition)
──────────────────────────────────────────────────────
Reaction: CH₂=CH₂ + Br₂  →  CH₂Br-CH₂Br
                              (1,2-dibromoethane)

STEP 1 — Pi electrons attack Br₂:
    CH₂=CH₂  +  Br-Br
         ↓ (π electrons attack positive end of Br₂)
    
    Cyclic BROMONIUM ION forms:
         Br⁺
        / \
    CH₂   CH₂     +  Br⁻
    
    (Bridged 3-membered ring — prevents free rotation)

STEP 2 — Br⁻ attacks ANTI:
    Br⁻ attacks from the BACK side (anti to bridging Br)
    → Anti addition (trans product)
    
    Result: CH₂Br-CH₂Br  (anti added, trans)
──────────────────────────────────────────────────────

Evidence for Bromonium Ion:

• Anti addition is observed (not syn)
• Reaction is stereospecific
• In protic solvents, water can also attack → halohydrin forms

Bromine Test:

Alkene + Br₂ (in CCl₄)  →  Decolorization (brown → colorless)
This is a positive test for unsaturation (C=C bond)

---

Q3. Orientation in Free Radical Addition

Markovnikov vs Anti-Markovnikov:

ORIENTATION IN ADDITION REACTIONS
──────────────────────────────────────────────────────
Markovnikov's Rule (IONIC/Electrophilic addition):
"H adds to the carbon bearing MORE H atoms"
(equivalent: electrophile adds to give more stable carbocation)

    HBr + CH₃CH=CH₂
    → CH₃-CH(Br)-CH₃  (Markovnikov — MAJOR in ionic)
    (Br on more substituted carbon, 2° carbocation)

Anti-Markovnikov (FREE RADICAL addition):
"Br• adds to LESS substituted carbon"
(because more stable radical forms at more substituted carbon)

    HBr + CH₃CH=CH₂  [PEROXIDE]
    → CH₃-CH₂-CH₂Br  (Anti-Markovnikov — MAJOR)
    (Br on less substituted carbon, 2° radical forms)
──────────────────────────────────────────────────────

Why the Difference?

Ionic (no peroxide):   H⁺ adds first → carbocation intermediate
                        (more stable carbocation = 2°/3° carbon)
                        → Markovnikov

Radical (peroxide):     Br• adds first → radical intermediate
                        (more stable radical = 2°/3° carbon)
                        → Br on the more substituted C
                        → H on the less substituted C
                        = Anti-Markovnikov (for HBr product position)

---

Q4. Mechanism of Peroxide-Initiated Addition

Peroxide-Initiated Chain Mechanism:

PEROXIDE INITIATION — DETAILED MECHANISM
──────────────────────────────────────────────────────
Initiator: ROOR (dibenzoyl peroxide, for example)

INITIATION:
  PhCO-O-O-COPh  →[Δ or hν]→  2 PhCO-O•
  PhCOO•  →  Ph• + CO₂  (further fragmentation)
  Ph• + HBr  →  PhH + Br•

PROPAGATION (Chain):
  Step 1: Br• + CH₂=CH₂  →  •CH₂CH₂Br
          (Br• adds to double bond, carbon radical forms)
  
  Step 2: •CH₂CH₂Br + HBr  →  BrCH₂CH₂Br + Br•
          (H abstracted from HBr, Br• regenerated)
  
  Chain length = hundreds to thousands of cycles

TERMINATION:
  2 Br•  →  Br₂
  2 R•   →  R-R
  Br• + R•  →  R-Br
──────────────────────────────────────────────────────

Why Br• and Not H•?

BDE comparison:
  H-Br bond: 366 kJ/mol
  Br-Br bond: 193 kJ/mol

Br• adds to alkene (step 1) because:
→ Br-C bond forms (strong) and radical is on C (stabilized)
→ H• adds to alkene would give less stable radical
→ Thermodynamics favors Br• addition

---

Q5. Electrophilic Addition to Alkenes

General Mechanism:

ELECTROPHILIC ADDITION — GENERAL MECHANISM
──────────────────────────────────────────────────────
E-Nu  (electrophile-nucleophile pair; e.g., HBr, H₂SO₄)

Step 1: Pi electrons attack the electrophile (E⁺):
    C=C  +  E⁺  →  C⁺-C-E
              (carbocation intermediate)

Step 2: Nucleophile (Nu:⁻) attacks carbocation:
    C⁺-C-E  +  Nu:⁻  →  Nu-C-C-E
              (addition product)
──────────────────────────────────────────────────────

Examples of Electrophilic Additions:

1. Addition of HBr (Markovnikov):
   CH₃CH=CH₂ + HBr → CH₃CHBrCH₃
   
2. Addition of H₂SO₄:
   CH₂=CH₂ + H₂SO₄ → CH₃CH₂OSO₃H (ethyl hydrogen sulfate)
   
3. Addition of H₂O (acid-catalyzed hydration):
   CH₂=CH₂ + H₂O → CH₃CH₂OH (Markovnikov)
   
4. Addition of Cl₂ / Br₂ (via halonium ion):
   CH₂=CH₂ + Br₂ → CH₂BrCH₂Br (anti addition)
   
5. Oxymercuration-demercuration:
   CH₂=CH₂ + Hg(OAc)₂/H₂O → Markovnikov alcohol

Markovnikov's Rule in Electrophilic Addition:

"The electrophile (H⁺) adds to the carbon with 
 MORE hydrogens (less substituted carbon)"

This is because the MORE STABLE CARBOCATION forms:
   
   3° carbocation > 2° > 1° (stability)
   
   H adds to less substituted C → more substituted C⁺ → stable

---

Q6. Addition of Carbene to Alkene

What is a Carbene?

STRUCTURE OF CARBENE:
    :CH₂  or  :CX₂

  Carbon has:
  - 2 bonds to other atoms
  - No charge
  - 2 non-bonding electrons (can be paired = singlet,
    or unpaired = triplet)

Types:
  Singlet carbene: ↑↓ (paired electrons, reactive)
  Triplet carbene: ↑  ↑ (diradical, less reactive)

Addition of Carbene to Alkene (Cyclopropane Formation):

CARBENE ADDITION TO ALKENES
──────────────────────────────────────────────────────
Reaction: Alkene + :CH₂ → Cyclopropane

   CH₂=CH₂  +  :CH₂  →  cyclopropane (triangle ring)
   
         CH₂
        / \
    CH₂   CH₂
   (cyclopropane)

Mechanism:
Singlet carbene adds in ONE STEP:
   :CH₂ donates and accepts electrons simultaneously
   → Syn addition (both bonds form from same side)
   → Stereospecific
──────────────────────────────────────────────────────

Generation of Carbene:

1. From CHCl₃ + strong base (KOH):
   CHCl₃  →  :CCl₂  (dichlorocarbene)

2. From diazomethane (photolysis):
   CH₂N₂  →[hν]→  :CH₂  +  N₂

3. Simmons-Smith reaction:
   CH₂I₂ + Zn → carbenoid (IZnCH₂I)
   Reacts with alkenes to give cyclopropane

---

═══════════════════════════════════

UNIT 6 — RESONANCE & ALLYLIC/ALKYLIC SYSTEMS

═══════════════════════════════════

---

Q1. Allylic Cation as Resonance Hybrid

Formation:

Allyl cation forms when:
   CH₂=CH-CH₂⁺  ←→  CH₂⁺-CH=CH₂
   
   (Charge delocalized over 3 carbons)

Resonance Hybrid:

ALLYLIC CATION RESONANCE
──────────────────────────────────────────────────────
Structure 1:              Structure 2:
CH₂=CH-CH₂⁺              ⁺CH₂-CH=CH₂
(charge on C3)            (charge on C1)

         ↕ RESONANCE (double-headed arrow)
         
HYBRID (actual structure):
     δ⁺          δ⁺
   CH₂ — CH — CH₂
   
   (partial positive charge on BOTH terminal carbons)
   (C-C bond order = 1.5 in hybrid — between single and double)
──────────────────────────────────────────────────────

MO (Molecular Orbital) Picture:

Allylic cation: 3 p-orbitals overlap
   p   p   p
   |   |   |
   C = C — C⁺  →  delocalized π system
   
   Empty π* orbital is the LUMO (electrophile)

Nucleophilic Attack on Allylic Cation:

---

Q2. Stability of Conjugated Dienes

TYPES OF DIENES:
────────────────────────────────────────────
Isolated diene:    C=C-C-C=C  (not conjugated)
                   (more than one single bond between C=C)

Conjugated diene:  C=C-C=C    (one single bond between)
                   
Cumulated diene:   C=C=C      (no single bond, allene)
────────────────────────────────────────────

Why Conjugated Dienes are More Stable:

STABILITY FACTORS:
──────────────────────────────────────────────────────
1. RESONANCE / DELOCALIZATION:
   In 1,3-butadiene (conjugated):
   
   CH₂=CH-CH=CH₂   ←→   CH₂⁻-CH=CH-CH₂⁺
   
   Pi electrons are delocalized over ALL 4 carbons
   → Lower energy (more stable)

2. HEAT OF HYDROGENATION:
   1,3-Butadiene (conjugated) + H₂:  ΔH = -239 kJ/mol
   1,4-Pentadiene (isolated) + H₂:   ΔH = -254 kJ/mol/mole
   
   Conjugated diene releases LESS energy → it is MORE stable
   (Extra stability ≈ 15 kJ/mol = delocalization energy)

3. C-C SINGLE BOND LENGTH:
   Normal C-C: 1.54 Å
   Single bond in conjugated diene: 1.46 Å
   (Partial double bond character due to delocalization)
──────────────────────────────────────────────────────

s-cis and s-trans Conformations:

s-cis (reactive for Diels-Alder):
     /\
    /  \
C=C    C=C   (same side)

s-trans (predominant, more stable, but not reactive in D-A):
    /         \
   /           \
  C=C          C=C  (opposite sides)

---

Q3. 1,2-Addition vs 1,4-Addition

1,2 vs 1,4 ADDITION TO CONJUGATED DIENE
──────────────────────────────────────────────────────
Example: 1,3-Butadiene + HBr
           
   1    2    3    4
   CH₂=CH-CH=CH₂
   
   After H⁺ adds at C1:
   
   ⁺CH₂-CH=CH-CH₃  → Allylic cation (resonance)
   
        ↓               ↓
   Br⁻ attacks C2      Br⁻ attacks C4
        ↓               ↓
   3-Bromo-1-butene   1-Bromo-2-butene
   (1,2-product)      (1,4-product)
──────────────────────────────────────────────────────

Which Product Predominates?

KINETIC vs THERMODYNAMIC CONTROL:

KINETIC CONTROL (low T, fast):
→ 1,2-addition product predominates
→ Br⁻ attacks the more accessible C2 (closer)
→ Formed FASTER (lower activation energy)

THERMODYNAMIC CONTROL (high T, equilibrium):
→ 1,4-addition product predominates
→ More substituted alkene = more stable = thermodynamic product
→ Formed at HIGHER temperatures (reversible)

---

Q4. Hyperconjugation

Diagram:

HYPERCONJUGATION IN CARBOCATIONS
──────────────────────────────────────────────────────
Ethyl carbocation (CH₃-CH₂⁺):

    H                H
    |                |
H — C — C⁺   →   H — C⊕ = C  (no-bond resonance)
    |                |
    H                H

The C-H bonding orbital overlaps with empty p orbital on C⁺
This delocalizes electron density onto the cation center
→ Stabilizes the carbocation
──────────────────────────────────────────────────────

Hyperconjugation in Alkenes:

More alkyl substituents on C=C → more C-H bonds adjacent to pi
→ More hyperconjugation → more stable alkene

Stability of alkenes:
   R₂C=CR₂ > R₂C=CHR > RCH=CHR > CH₂=CH₂
   (tetrasubstituted)                (unsubstituted)
   Most stable                    Least stable

Key Points:

---

Q5. Resonance Stabilization of Allylic Cation

Energy of Stabilization:

Regular carbocation (no resonance):
    CH₃CH₂⁺  (2° would be CH₃CH⁺CH₃)
    
Allylic carbocation (resonance):
    CH₂=CH-CH₂⁺  ←→  ⁺CH₂-CH=CH₂
    
    ~70 kJ/mol more stable than comparable alkyl cation
    (due to resonance delocalization)

MO Description:

3 p-orbitals  →  3 MOs (π₁, π₂, π₃)

ψ₃ (LUMO, antibonding)   ─── (empty)
ψ₂ (HOMO, non-bonding)   ─── (empty in cation)
ψ₁ (bonding)             ↑↓ (2 electrons)

In allylic cation: 2 electrons in ψ₁
Charge distributed across C1 and C3 (terminal carbons)

---

Q6. Alkyl Radicals as Resonance Hybrids

ALLYLIC RADICAL AS RESONANCE HYBRID
──────────────────────────────────────────────────────
Structure 1:              Structure 2:
CH₂=CH-CH₂•              •CH₂-CH=CH₂
(radical on C3)           (radical on C1)

          ↕ RESONANCE
          
HYBRID:
     δ•         δ•
   CH₂ — CH — CH₂
   
   (Unpaired electron delocalized on BOTH terminal carbons)
──────────────────────────────────────────────────────

3-MO Description of Allylic Radical:

ψ₃ (antibonding)   ─── (empty)
ψ₂ (non-bonding)   ─ (1 electron — unpaired radical electron)
ψ₁ (bonding)       ↑↓ (2 electrons)

The unpaired electron occupies the NON-BONDING MO
→ Delocalized over C1 and C3 → STABLE

Ph-CH₂•  ←→  •Ph=CH₂ (through multiple ring structures)
(Delocalized into benzene ring → very stable)

---

═══════════════════════════════════

UNIT 7 — AROMATIC ELECTROPHILIC SUBSTITUTION

═══════════════════════════════════

---

Q1. Mechanism of Nitration

Mechanism:

NITRATION OF BENZENE
──────────────────────────────────────────────────────
STEP 1 — GENERATION OF ELECTROPHILE (Nitronium ion, NO₂⁺):
    HNO₃  +  H₂SO₄  →  NO₂⁺  +  HSO₄⁻  +  H₂O
    (H₂SO₄ protonates HNO₃, water leaves → NO₂⁺)

STEP 2 — ELECTROPHILIC ATTACK (slow, rate-determining):
    Benzene π electrons attack NO₂⁺:
    
    [Benzene ring] + NO₂⁺  →  [Arenium ion / sigma complex]
         ─ loss of aromaticity ─
         
    The sigma complex (Wheland intermediate) = 
    cyclohexadienyl cation with NO₂ attached

STEP 3 — DEPROTONATION (fast):
    [Arenium ion] + HSO₄⁻  →  Nitrobenzene + H₂SO₄
    (H⁺ lost → aromaticity restored → DRIVING FORCE)
──────────────────────────────────────────────────────

Energy Diagram:

Energy
  |    TS1 (slow)   TS2 (fast)
  |   /     \       /     \
  |  /   Sigma \   /        \
  | /   complex \  /          \
  |/              \/            \
Benzene       Arenium ion    Nitrobenzene
+ NO₂⁺        (intermediate)

---

Q2. Mechanism of Sulfonation

SULFONATION OF BENZENE
──────────────────────────────────────────────────────
ELECTROPHILE: SO₃ or ⁺SO₃H (from fuming H₂SO₄ = oleum)

STEP 1 — ELECTROPHILE GENERATION:
    H₂SO₄ (conc.)  →  SO₃ + H₂O  (or use oleum directly)

STEP 2 — ELECTROPHILIC ATTACK:
    Benzene + SO₃  →  Sigma complex (arenium ion with SO₃⁻)

STEP 3 — DEPROTONATION:
    Sigma complex + H₂O  →  C₆H₅SO₃H + H⁺
    (Benzenesulfonic acid)
──────────────────────────────────────────────────────

---

Q3. Mechanism of Halogenation of Benzene

HALOGENATION OF BENZENE (Electrophilic)
──────────────────────────────────────────────────────
ELECTROPHILE GENERATION:
    Br₂ + FeBr₃ (Lewis acid)  →  Br⁺-FeBr₄⁻  (activated Br)
    OR simply Br-Br with FeBr₃ polarizes the Br-Br bond

STEP 1 — ELECTROPHILIC ATTACK:
    Benzene + Br⁺  →  [Sigma complex / arenium ion]
    
              Br
              |
        (ring loses one double bond, H still there)

STEP 2 — DEPROTONATION:
    [Arenium ion] + FeBr₄⁻  →  Bromobenzene + HBr + FeBr₃
    (FeBr₃ catalyst regenerated)
──────────────────────────────────────────────────────

• Br₂ is not electrophilic enough to attack aromatic ring alone
• FeBr₃ polarizes Br₂ → makes one Br more electrophilic

---

Q4. Mechanism of Friedel-Crafts Acylation

FRIEDEL-CRAFTS ACYLATION
──────────────────────────────────────────────────────
STEP 1 — ELECTROPHILE GENERATION (Acylium ion):
    RCO—Cl + AlCl₃  →  RCO⁺  +  AlCl₄⁻
    (Acylium ion = R-C≡O⁺, resonance-stabilized)

STEP 2 — ELECTROPHILIC ATTACK:
    Benzene + RCO⁺  →  [Sigma complex / Arenium ion]
    
        CO-R
        |
    (ring with + charge delocalized)

STEP 3 — DEPROTONATION:
    [Arenium ion] + AlCl₄⁻  →  Aryl ketone + HCl + AlCl₃
──────────────────────────────────────────────────────

• No rearrangement (acylium is stable, doesn't rearrange)
• Gives one pure product (no polyacylation because product is deactivated)

• Needs anhydrous conditions (water destroys AlCl₃)

---

Q5. Mechanism of Friedel-Crafts Alkylation

FRIEDEL-CRAFTS ALKYLATION
──────────────────────────────────────────────────────
STEP 1 — CARBOCATION GENERATION:
    R—Cl + AlCl₃  →  R⁺  +  AlCl₄⁻
    (Carbocation formed — can REARRANGE)

STEP 2 — ELECTROPHILIC ATTACK:
    Benzene + R⁺  →  [Sigma complex / Arenium ion]

STEP 3 — DEPROTONATION:
    [Arenium ion] + AlCl₄⁻  →  Alkylbenzene + HCl + AlCl₃
──────────────────────────────────────────────────────

Limitations of Friedel-Crafts Alkylation:

LIMITATIONS:
──────────────────────────────────────────────────────
1. REARRANGEMENT: Carbocation can rearrange
   n-propyl chloride → isopropyl group on ring
   (Carbocation rearranges to more stable form)

2. POLYALKYLATION: Product is more reactive than benzene
   Alkyl group activates ring → multiple alkylations occur
   
3. FAILS WITH DEACTIVATED BENZENES:
   Nitrobenzene, benzaldehyde (EWG on ring = deactivated ring)
   
4. ONLY WORKS WITH ACYL HALIDES OR ALKYL HALIDES
   (not with alkenes alone, unless acid catalyst present)
──────────────────────────────────────────────────────

---

Q6. Side Chain Halogenation of Alkylbenzene

SIDE CHAIN HALOGENATION (Free Radical)
──────────────────────────────────────────────────────
Example: Toluene + Cl₂ →[hν]→ Benzyl chloride + HCl

    Ph-CH₃  +  Cl₂  →[hν]→  Ph-CH₂Cl  +  HCl

MECHANISM:
INITIATION:    Cl₂ →[hν]→ 2Cl•
PROPAGATION:   Cl• + Ph-CH₃ → Ph-CH₂• + HCl
               Ph-CH₂• + Cl₂ → Ph-CH₂Cl + Cl•
TERMINATION:   2 Cl• → Cl₂, 2 Ph-CH₂• → bibenzyl, etc.

WHY BENZYLIC POSITION IS SELECTIVE?
   Ph-CH₂• (benzylic radical) is VERY STABLE
   (delocalized into benzene ring)
   → Reaction at benzylic position is favored
──────────────────────────────────────────────────────

Ring vs Side Chain Halogenation:

CONDITION            WHERE HALOGENATION OCCURS
─────────────────────────────────────────────
With Lewis acid     Ring (electrophilic, EAS)
(FeBr₃, AlCl₃)
─────────────────────────────────────────────
With Light (hν)     Side chain (free radical)
or Heat
─────────────────────────────────────────────

---

═══════════════════════════════════

UNIT 8 — CARBOXYLIC ACIDS & DERIVATIVES

═══════════════════════════════════

---

Q1. Ionization of Carboxylic Acid

IONIZATION OF CARBOXYLIC ACID
──────────────────────────────────────────────────────
Ionization equation:
    CH₃COOH  +  H₂O  ⇌  CH₃COO⁻  +  H₃O⁺

Acid dissociation constant (Ka):
    Ka = [CH₃COO⁻][H₃O⁺] / [CH₃COOH]
    
    For acetic acid: Ka = 1.8 × 10⁻⁵ (weak acid)
    pKa = 4.74

The CARBOXYLATE ANION (RCO₂⁻) is stabilized by resonance:
    O             O⁻
    ‖             |
R—C—O⁻   ←→  R—C=O
(Two equivalent resonance structures)
→ Charge delocalized over both oxygens
→ Lower energy = more stable → promotes ionization
──────────────────────────────────────────────────────

---

Q2. Acidity of Carboxylic Acids and Structure of Carboxylate Ion

Why Carboxylic Acids are More Acidic than Alcohols:

ACID STRENGTH COMPARISON
──────────────────────────────────────────────────────
Carboxylic acid pKa ≈ 4-5  (stronger acid)
Alcohol pKa ≈ 15-16         (much weaker acid)
Water pKa = 15.7

REASON:
Alcohol ionizes: ROH → RO⁻ + H⁺
   Alkoxide (RO⁻) = charge on ONE oxygen only = UNSTABLE

Carboxylic acid ionizes: RCOOH → RCOO⁻ + H⁺
   Carboxylate (RCOO⁻) = charge on TWO oxygens (resonance)
   → MUCH MORE STABLE → equilibrium favors ionization
──────────────────────────────────────────────────────

Structure of Carboxylate Ion:

   O         O⁻
   ‖          |
R—C—O⁻  ←→  R—C=O
             
HYBRID (actual structure):
      O^(δ-)
      |
  R—C          Both C-O bonds are EQUAL (1.25 Å)
      |         (between C=O of 1.22 Å and C-O of 1.36 Å)
      O^(δ-)
      
Bond angle at C = 120° (sp² hybridized carbon)

Effect of Substituents on Acid Strength:

Electron-withdrawing groups (EWG) → stronger acid
   (stabilize carboxylate by further delocalization)
   
   CCl₃COOH > CHCl₂COOH > CH₂ClCOOH > CH₃COOH
   (strongest)                          (weakest)

Electron-donating groups (EDG) → weaker acid
   (destabilize carboxylate)
   
   pKa order confirms inductive effects

---

Q3. Nucleophilic Substitution at Acyl Carbon (Acyl Substitution)

ACYL NUCLEOPHILIC SUBSTITUTION (Addition-Elimination)
──────────────────────────────────────────────────────
General mechanism:

         O                    O⁻                O
         ‖                    |                 ‖
    R — C — LG  +  Nu:  →  R—C—LG    →   R — C — Nu  +  LG⁻
    (acyl compound)          |
                             Nu
                         (tetrahedral
                          intermediate)

Step 1: ADDITION — Nu attacks carbonyl carbon
Step 2: ELIMINATION — LG departs, C=O reforms
──────────────────────────────────────────────────────

Reactivity of Acyl Compounds:

REACTIVITY ORDER (ease of nucleophilic attack):

Acyl halide > Anhydride > Ester > Amide
  (most                              (least
  reactive)                         reactive)

Reason: Better the leaving group, more reactive.
  Cl⁻ > RCOO⁻ > RO⁻ > NR₂⁻ (leaving ability)

---

Q4. Conversion of Acid to Acid Chloride

Methods:

CONVERSION OF CARBOXYLIC ACID TO ACID CHLORIDE
──────────────────────────────────────────────────────
Method 1: Using Thionyl Chloride (SOCl₂) — BEST METHOD:
    RCOOH + SOCl₂ → RCOCl + SO₂ + HCl
    
    Advantages: SO₂ and HCl gases leave → pure product
    Conditions: Room temperature or mild heat
    
Method 2: Using PCl₅ (phosphorus pentachloride):
    RCOOH + PCl₅ → RCOCl + POCl₃ + HCl
    
    Disadvantage: POCl₃ is liquid → harder to separate
    
Method 3: Using PCl₃:
    3RCOOH + PCl₃ → 3RCOCl + H₃PO₃
──────────────────────────────────────────────────────

Mechanism (SOCl₂):

Step 1: O-H attacks SOCl₂:
    RCOOH + Cl-S(=O)-Cl → RCOO-S(=O)-Cl + HCl
    (mixed anhydride intermediate)

Step 2: Cl⁻ attacks carbonyl carbon:
    RCOO-S(=O)-Cl → RC(=O)Cl + SO₂
    (SO₂ gas evolved → drives reaction forward)

---

Q5. Alkyl Substitution Reactions (Nucleophilic Acyl Substitution)

REACTIONS OF ACID DERIVATIVES
──────────────────────────────────────────────────────
1. Acid Chloride + H₂O → Carboxylic acid + HCl (hydrolysis)
2. Acid Chloride + ROH → Ester + HCl (esterification)
3. Acid Chloride + NH₃ → Amide + HCl (amide formation)
4. Acid Chloride + LiAlH₄ → Alcohol (reduction)
5. Ester + NaOH → Carboxylate + Alcohol (saponification)
6. Ester + NH₃ → Amide + Alcohol
7. Amide + H₂O/H⁺ → Acid + NH₄⁺ (hydrolysis)
──────────────────────────────────────────────────────

---

Q6. Rosenmund Reduction

ROSENMUND REDUCTION
──────────────────────────────────────────────────────
Reaction:
    RCOCl  +  H₂  →[Pd-BaSO₄]→  RCHO  +  HCl

Why poisoned catalyst?
  Normal Pd would reduce further → alcohol (RCH₂OH)
  Pd/BaSO₄ (quinoline poisoned) = PARTIAL activity
  → Stops at aldehyde stage

Example:
    CH₃CH₂COCl + H₂ → [Pd-BaSO₄] → CH₃CH₂CHO + HCl
    Propanoyl chloride                   Propanal

Mechanism:
  Surface reaction on Pd catalyst
  H₂ adsorbs on catalyst surface
  Cl replaced by H selectively
──────────────────────────────────────────────────────

---

═══════════════════════════════════

UNIT 9 — AMINES, PHENOLS & DIAZONIUM

═══════════════════════════════════

---

Q1. Basicity of Amines

BASIC BEHAVIOR OF AMINES
──────────────────────────────────────────────────────
RNH₂  +  H₂O  ⇌  RNH₃⁺  +  OH⁻
Amine           Ammonium ion   (base behavior)

Kb expression:
    Kb = [RNH₃⁺][OH⁻] / [RNH₂]
    
pKb for typical amines ≈ 3-4  (weak bases)
──────────────────────────────────────────────────────

Order of Basicity:

IN GAS PHASE:
    3° amine > 2° amine > 1° amine > NH₃
    (More alkyl groups = more electron donation to N)

IN AQUEOUS SOLUTION:
    2° amine > 1° amine > 3° amine > NH₃
    
    (3° amine is less basic in water because 
     the large alkyl groups prevent solvation 
     of the bulky ammonium ion)
     
Aromatic amines (aniline) are MUCH WEAKER bases:
    Aniline pKb ≈ 9.4  vs  Et-NH₂ pKb ≈ 3.3
    
    (Lone pair on N is delocalized into benzene ring
     → less available to accept H⁺ → weaker base)

---

Q2. Diazotization and Coupling Reactions

A) Diazotization

DIAZOTIZATION REACTION
──────────────────────────────────────────────────────
Ar-NH₂  +  NaNO₂  +  2HCl  →[0-5°C]→  Ar-N₂⁺Cl⁻  +  NaCl + 2H₂O
                                         (diazonium salt)

Example:
    C₆H₅-NH₂  +  NaNO₂  +  2HCl  →[0-5°C]→  C₆H₅-N₂⁺Cl⁻
    Aniline                                    Benzenediazonium chloride

Mechanism:
    HNO₂ (from NaNO₂ + HCl) → [NO⁺] (nitrosonium ion)
    Ar-NH₂ + NO⁺ → Ar-NH-NO → Ar-N=N-OH → Ar-N₂⁺
──────────────────────────────────────────────────────

• Diazonium salts are UNSTABLE above 5°C — they decompose to phenol
• Low temperature stabilizes the diazonium salt

B) Coupling Reaction

COUPLING REACTION
──────────────────────────────────────────────────────
Ar-N₂⁺  +  Ar'-H  →  Ar-N=N-Ar'  +  H⁺
                       (azo compound — intensely colored)

With Phenol:
    Ph-N₂⁺  +  HO-C₆H₄-H  →  Ph-N=N-C₆H₄-OH
    (in alkaline medium, para position attacked)
    Orange-red color → azo dye

With Aniline:
    Ph-N₂⁺  +  H₂N-C₆H₄-H  →  Ph-N=N-C₆H₄-NH₂
    (in neutral/acidic medium, para position attacked)
    Yellow/orange color
──────────────────────────────────────────────────────

---

Q4. Hofmann Rearrangement

HOFMANN REARRANGEMENT (Hofmann Degradation)
──────────────────────────────────────────────────────
Reaction:
    RCONH₂  +  Br₂  +  4NaOH  →  R-NH₂  +  Na₂CO₃ + 2NaBr + 2H₂O
    (amide)                        (amine — one C less!)

Example:
    CH₃CONH₂  →  CH₃NH₂  (acetamide → methylamine)

MECHANISM:
Step 1: Br₂ + NaOH → NaOBr (hypobromite)
Step 2: N-H of amide is brominated:
        RCONH₂ + NaOBr → RCONHB + NaOH
        → RCONBr⁻ (N-bromo amide anion)

Step 3: REARRANGEMENT (key step):
        N → C migration:
        RCO-N:Br  →  R-N=C=O  (isocyanate)
        [The R group migrates from C to N]

Step 4: Isocyanate hydrolysis:
        R-N=C=O  +  NaOH  →  R-NHCOO⁻  →  R-NH₂  +  CO₂
──────────────────────────────────────────────────────

---

Q5. Bimolecular Displacement (SN2) Reactions

R-NH₂  +  R'-X  →  R-NH-R'  +  X⁻  (2° amine)
2° amine + R'-X  →  3° amine
3° amine + R'-X  →  R₄N⁺X⁻  (quaternary ammonium salt)

---

Q6. Acidity of Phenol

IONIZATION OF PHENOL
──────────────────────────────────────────────────────
C₆H₅-OH  +  H₂O  ⇌  C₆H₅-O⁻  +  H₃O⁺
   pKa ≈ 10 (much more acidic than ethanol, pKa ≈ 16)

WHY PHENOL IS MORE ACIDIC THAN ALCOHOL:

Phenoxide ion resonance:

    O⁻         O            O            O
    |         ‖            |            ‖
 [benzene] ← C₆H₄ ←→ different ring positions
 
 5 resonance structures delocalize the negative charge
 over the oxygen AND into the ring
 → Very stable anion → Equilibrium favors ionization
──────────────────────────────────────────────────────

Comparison:

---

Q7. Migration to Electron-Deficient Nitrogen (Nitrene Rearrangements)

ELECTRON-DEFICIENT NITROGEN (Nitrene)
──────────────────────────────────────────────────────
Nitrene: R-N: (nitrogen with lone pair but only 6e⁻)

Example — CURTIUS REARRANGEMENT:
    R-CO-N₃  →[Δ]→  [R-CO-N:]  →  R-N=C=O  +  N₂
    (Acyl azide)    (nitrene)     (isocyanate)
    
    The R group migrates from C to N → isocyanate
    Hydrolysis gives amine (1 carbon shorter)

BECKMANN REARRANGEMENT:
    Oxime  →[H₂SO₄]→  Amide (via N migration)
    R-C(=NOH)-R'  →  R-CO-NHR'  or  R'-CO-NHR
    
    Anti group migrates (anti to OH) → specific product
──────────────────────────────────────────────────────

---

═══════════════════════════════════

UNIT 10 — PHARMACEUTICAL / MEDICINAL CHEMISTRY

═══════════════════════════════════

---

Q1. Glyceryl Trinitrate (Nitroglycerin) — Preparation and Medicinal Use

Preparation:

PREPARATION OF GLYCERYL TRINITRATE
──────────────────────────────────────────────────────
Reaction: Glycerol + Nitric acid (mixed acid)
    
    CH₂-OH              CH₂-ONO₂
    |                   |
    CH-OH + 3HNO₃  →    CH-ONO₂  +  3H₂O
    |         (H₂SO₄)   |
    CH₂-OH              CH₂-ONO₂
    (Glycerol)          (Glyceryl trinitrate)
    
Conditions:
  - Mixed acid = concentrated HNO₃ + conc. H₂SO₄
  - Temperature maintained below 10°C (exothermic!)
  - Careful addition to avoid explosion
  - Product washed with Na₂CO₃ to remove acid
  - Diluted in lactose or propylene glycol for safety
──────────────────────────────────────────────────────

Medicinal Uses:

MEDICINAL USES OF GTN
─────────────────────────────────────────────────────
1. ANGINA PECTORIS:
   → First-line treatment for chest pain from coronary artery disease
   → Sublingual tablet, spray, or patch
   → Acts within 1-3 minutes (sublingual)

2. MECHANISM OF ACTION:
   GTN → releases Nitric Oxide (NO) in body
   NO → activates guanylyl cyclase → ↑ cGMP
   cGMP → smooth muscle relaxation → vasodilation
   → Coronary arteries dilate → more O₂ to heart muscle

3. HEART FAILURE:
   → Reduces preload (venodilation) and afterload
   → Used in acute pulmonary edema

4. HYPERTENSION (IV form):
   → Controlled hypotension in surgery
─────────────────────────────────────────────────────

Structure:

    H₂C—O—NO₂
    |
    HC—O—NO₂
    |
    H₂C—O—NO₂
    
(Three nitrate ester groups on glycerol backbone)

---

Q2. Ethyl Benzoate — Purity Test and Medicinal Use

Preparation:

Benzoic acid + Ethanol → Ethyl benzoate + Water
C₆H₅COOH + C₂H₅OH ⇌ C₆H₅COOC₂H₅ + H₂O
(Fischer esterification with H₂SO₄ catalyst)

Purity Tests:

PURITY TESTS FOR ETHYL BENZOATE
─────────────────────────────────────────────────────
1. APPEARANCE: Colorless, oily liquid (clear)
   → Impure sample = turbid or colored

2. ODOR TEST: Characteristic pleasant fruity/floral smell
   → Rancid smell = impure

3. BOILING POINT: 213°C (pure)
   → Deviation from standard = impurity

4. REFRACTIVE INDEX: nD²⁰ = 1.5045 (standard value)

5. SAPONIFICATION VALUE:
   → Hydrolysis with NaOH:
   C₆H₅COOC₂H₅ + NaOH → C₆H₅COONa + C₂H₅OH
   → Amount of NaOH used confirms purity/ester content

6. DENSITY: 1.05 g/cm³
   → Significant variation = contamination
─────────────────────────────────────────────────────

Medicinal/Industrial Uses:

1. Perfumery and cosmetics (fragrance compound)
2. Flavoring agent (food industry)
3. Insect repellent properties
4. Pharmaceutical solvent and excipient
5. Used in synthesis of other benzoate compounds

---

Q3. Para Chloride (p-Dichlorobenzene)

Structure:

        Cl
        |
    [benzene ring]
        |
        Cl
    (Cl at 1 and 4 positions = para)

Preparation:

Benzene + Cl₂ →[FeCl₃, 25°C]→ Chlorobenzene + HCl
Chlorobenzene + Cl₂ →[FeCl₃]→ 1,2- + 1,4-dichlorobenzene
                                (ortho + para mixture)
                                (separated by distillation)

Uses:

USES OF p-DICHLOROBENZENE
─────────────────────────────────────────────────────
1. MOTH REPELLENT / Insecticide (most common use)
   → "Moth balls" (replaced naphthalene in some countries)
   
2. DEODORANT / Air freshener
   → Solid room deodorizer

3. CHEMICAL INTERMEDIATE:
   → Synthesis of polyphenylene sulfide (polymer)
   → Synthesis of dyes and agrochemicals

4. SOLVENT for some industrial processes

Physical properties:
  MP: 53°C (solid at room temperature)
  Sublimes readily → volatilizes slowly (moth repellent action)
─────────────────────────────────────────────────────

---

Q4. Ethyl Benzene — Study

Structure:

    [Benzene ring]—CH₂—CH₃
    
    Phenyl group attached to an ethyl group

Preparation:

PREPARATION
─────────────────────────────────────────────────────
Method 1: Friedel-Crafts Alkylation
    C₆H₆ + CH₃CH₂Cl →[AlCl₃]→ C₆H₅CH₂CH₃ + HCl

Method 2: Industrial (Catalytic alkylation):
    Benzene + Ethylene →[BF₃ or ZSM-5 zeolite]→ Ethylbenzene
    C₆H₆ + CH₂=CH₂ → C₆H₅CH₂CH₃
─────────────────────────────────────────────────────

Properties and Reactions:

Physical: Colorless liquid, bp 136°C, insoluble in water

Chemical Reactions:
1. Combustion: C₈H₁₀ + O₂ → CO₂ + H₂O
2. EAS (ring): undergoes nitration, sulfonation
3. Side chain oxidation: KMnO₄ → benzoic acid
4. Side chain halogenation: Cl₂/hν → 1-chloro-1-phenylethane

IMPORTANCE:
→ Over 99% of ethylbenzene is dehydrogenated to STYRENE:
    C₆H₅CH₂CH₃ →[600°C, Al₂O₃]→ C₆H₅CH=CH₂ + H₂
    Ethylbenzene                   Styrene (→polystyrene)

---

Q5. Tartaric Acid — Complete Study

Structure and Stereoisomers:

TARTARIC ACID STRUCTURE
──────────────────────────────────────────────────────
       COOH
        |
   HO—C—H       *chiral carbon
        |
   HO—C—H       *chiral carbon
        |
       COOH

Two chiral carbons → possible isomers:
1. L-(+)-tartaric acid (naturally occurring)
2. D-(−)-tartaric acid (unnatural)
3. meso-Tartaric acid (internally symmetric → optically inactive)
4. Racemic mixture (equal L and D → no optical activity)
──────────────────────────────────────────────────────

Properties:

PROPERTIES
─────────────────────────────────────────────────────
Physical: White crystalline solid, mp 171-174°C
          Soluble in water, slightly in alcohol

Chemical:
1. Dicarboxylic acid: pKa1 = 2.98, pKa2 = 4.34
2. Diol: reacts with periodic acid → cleaves C-C (oxidation)
3. Forms tartrates: Potassium hydrogen tartrate (cream of tartar)
4. Forms complexes with metal ions (chelation)
─────────────────────────────────────────────────────

Medicinal and Industrial Uses:

USES OF TARTARIC ACID
─────────────────────────────────────────────────────
1. FOOD INDUSTRY:
   → Acidulant and antioxidant (E334)
   → In soft drinks, confectionery, baking powder
   → Cream of tartar (KHC₄H₄O₆) in baking

2. PHARMACEUTICAL:
   → Effervescent tablets (reacts with NaHCO₃)
   → Antimony potassium tartrate ("tartar emetic")
   → Resolution of racemic mixtures (chiral resolution)

3. WINE INDUSTRY:
   → Natural product of grape fermentation
   → Stabilizes wine pH

4. CHEMICAL SYNTHESIS:
   → Chiral auxiliary in asymmetric synthesis
   → Dibenzoyl tartaric acid = resolving agent
─────────────────────────────────────────────────────

---

Q6. Ethylenediamine and Ethylenediamine Dihydroiodide — Purity Tests and Medicinal Uses

A) Ethylenediamine (EDA)

Purity Tests:

PURITY TESTS FOR ETHYLENEDIAMINE
─────────────────────────────────────────────────────
1. APPEARANCE: Colorless to slightly yellow liquid

2. ODOR: Ammoniacal/fishy smell
   → Foul or different odor = impure

3. BOILING POINT: 116°C (pure)
   → Deviation = impurity present

4. SPECIFIC GRAVITY: 0.899 g/mL at 20°C

5. pH TEST: 11.9 (10% aqueous solution)
   → Basic (contains two NH₂ groups)

6. COPPER COMPLEX TEST:
   EDA + CuSO₄ → deep blue color (chelate complex)
   → Color confirms EDA

7. WATER CONTENT:
   → Moisture content by Karl Fischer titration
   (hygroscopic, absorbs water)

8. TITRATION:
   → Acid-base titration with HCl (2 equiv. needed)
   → Both NH₂ groups titratable
─────────────────────────────────────────────────────

Medicinal Uses:

MEDICINAL USES OF ETHYLENEDIAMINE
─────────────────────────────────────────────────────
1. AMINOPHYLLINE:
   → Ethylenediamine salt of theophylline
   → Used for BRONCHIAL ASTHMA, COPD
   → Increases theophylline solubility

2. ANTIHISTAMINE:
   → Ethylenediamine structure is found in 
     1st-generation antihistamines
   → (e.g., diphenhydramine, tripelennamine)

3. CHELATING AGENT:
   → Backbone of EDTA (ethylenediaminetetraacetic acid)
   → Used to treat heavy metal poisoning

4. ANTIFUNGAL:
   → EDA-based compounds have antifungal properties
─────────────────────────────────────────────────────

B) Ethylenediamine Dihydriodide (EDDI)

Preparation:

EDA + 2HI → EDA·2HI  (ethylenediamine dihydroiodide)

Purity Tests:

PURITY TESTS FOR EDDI
─────────────────────────────────────────────────────
1. APPEARANCE: White crystalline powder

2. SOLUBILITY: Freely soluble in water

3. MELTING POINT: Check against standard value

4. IODIDE TEST:
   → Solution + AgNO₃ → yellow precipitate of AgI
   → Confirms iodide content

5. ASSAY (Iodine content):
   → Titration with Na₂S₂O₃ after oxidation
   → Confirms iodine % (theoretical ~75%)

6. HEAVY METAL TEST:
   → Check for Pb, As contamination (limit test)
─────────────────────────────────────────────────────

Medicinal Uses:

MEDICINAL USES OF EDDI
─────────────────────────────────────────────────────
1. VETERINARY MEDICINE:
   → Iodine supplement in animal feed
   → Treats and prevents iodine deficiency in livestock

2. IODINE SOURCE:
   → Organic iodine compound (better absorbed than
     inorganic iodide)

3. THYROID HEALTH:
   → Provides bioavailable iodine
   → Used in iodine-deficient regions

4. ANTISEPTIC properties (due to iodine content)
─────────────────────────────────────────────────────

---

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

QUICK REVISION FLOWCHARTS (SUMMARY)

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

Types of Isomerism — Master Flowchart:

ISOMERISM
    │
    ├── STRUCTURAL (Constitutional)
    │       ├── Chain isomerism (different skeleton)
    │       ├── Functional isomerism (different functional group)
    │       ├── Position isomerism (different position of group)
    │       └── Tautomerism (dynamic interconversion, keto-enol)
    │
    └── STEREOISOMERISM (same connectivity, different 3D arrangement)
            ├── Geometric (cis-trans)
            │       ├── Cis (same side)
            │       └── Trans (opposite sides)
            ├── Optical
            │       ├── Enantiomers (mirror images)
            │       ├── Diastereomers (non-mirror stereoisomers)
            │       └── Meso (chiral center but internally symmetric)
            └── Conformational (rotation about C-C)
                    ├── Staggered (stable)
                    └── Eclipsed (unstable)

Reaction Mechanism Decision Tree:

Is the substrate an alkene?
    YES → Addition reaction
           ├── With H-X (no peroxide): Markovnikov (ionic/electrophilic)
           ├── With H-X (+ peroxide): Anti-Markovnikov (free radical)
           └── With X₂: Anti addition via halonium ion

    NO → Is substrate a C-X (alkyl halide)?
           ├── Unimolecular (3° substrate, weak/no base): SN1 or E1
           └── Bimolecular (1°/2° substrate, strong base/nucleophile):
                   ├── Strong nucleophile, no steric → SN2
                   └── Bulky strong base, high T → E2

    NO → Is it aromatic (benzene)?
           └── EAS (electrophilic aromatic substitution)
                   ├── Nitration: HNO₃/H₂SO₄ → NO₂⁺
                   ├── Sulfonation: fuming H₂SO₄ → SO₃
                   ├── Halogenation: X₂/FeX₃ → X⁺
                   ├── Acylation: RCOCl/AlCl₃ → RCO⁺
                   └── Alkylation: RCl/AlCl₃ → R⁺