Identify Potential for Intramolecular Reaction:
- Look for carboxylic acids with additional functional groups that can participate in a ring closure.
Common Intramolecular Reactions:
- Lactonization:
  - Formation of a cyclic ester (lactone) from a hydroxy acid.
  - Mechanism:
    - Hydroxyl group attacks the carboxyl carbon.
    - Loss of water molecule (dehydration) to form a lactone.
  - Example:
    - 4-Hydroxybutanoic acid → γ-Butyrolactone.
- Lactamization:
  - Formation of a cyclic amide (lactam) from an amino acid.
  - Mechanism:
    - Amino group attacks the carboxyl carbon.
    - Loss of water molecule to form a lactam.
  - Example:
    - 4-Aminobutanoic acid → γ-Butyrolactam.

Hell-Volhard-Zelinsky (HVZ) Reaction:
- Identify Reactants:
  - Carboxylic acid (R-COOH)
  - Halogen (Br₂ or Cl₂)
  - Catalyst (PBr₃ or PCl₃)
- Reaction Mechanism:
  - Bromination of Carboxylic Acid:
    - PBr₃ converts the carboxylic acid to an acyl bromide.
    - Acyl bromide tautomerizes to an enol.
    - Enol reacts with Br₂ to form an α-bromo acyl bromide.
    - Hydrolysis of α-bromo acyl bromide to α-bromo carboxylic acid.
  - Example:
    - R-COOH + Br₂ + PBr₃ → α-Bromo carboxylic acid.
- Detailed Mechanism Steps:
  - R-COOH + PBr₃ → R-COBr (acyl bromide) + HBr.
  - R-COBr ⇌ Enol form (R=C(OH)-Br).
  - Enol reacts with Br₂ → α-Bromo acyl bromide (R-CBr=OBr).
  - Hydrolysis: R-CBr=OBr + H₂O → α-Bromo carboxylic acid (R-CHBr-COOH) + HBr.

Lesson 3: Carboxylic Acid Reactions: Intramolecular Reactions and HVZ Mechanism