The major product of the following reaction is:

Step 1: First reaction - Aqueous KOH

Dibromide + aqueous KOH → Substitution (not elimination)

$\ce{Br-CH2-CHBr-Ph + 2 OH- -> HO-CH2-CH(OH)-Ph + 2 Br-}$

Product: Diol (two OH groups)

Step 2: Second reaction - Oxidation with CrO₃/H⁺

Chromic acid oxidation:

• Primary alcohol → Carboxylic acid
• Secondary alcohol → Ketone

$\ce{HO-CH2-CH(OH)-Ph ->[CrO3/H+] HOOC-CO-Ph}$

Product: Keto acid

Step 3: Third reaction - Dehydration with H₂SO₄/Δ

Intramolecular esterification (lactone formation):

Keto acid cyclizes to form lactone (cyclic ester)

$\ce{HOOC-CO-Ph ->[H2SO4/Δ] Cyclic lactone}$

Answer: (b) Lactone structure

Key Reactions:

Lactone formation:

• Intramolecular esterification
• Hydroxy acid → Lactone + H₂O
• Favored for 5 and 6-membered rings
• Acid-catalyzed dehydration

Oxidation levels:

• 1° alcohol → Aldehyde → Carboxylic acid
• 2° alcohol → Ketone (no further oxidation)
• 3° alcohol → No oxidation

CrO₃/H⁺ (Jones reagent):

• Strong oxidizing agent
• Oxidizes 1° alcohols to carboxylic acids
• Oxidizes 2° alcohols to ketones