See image — Alcohols Phenols and Ethers Chemistry Question

💡 Solution & Explanation

Step 1 - Identify the starting material: The starting compound is 2-(2-oxoethyl)benzoic acid, i.e., a benzene ring bearing a carboxylic acid (-CO2H) at C1 and a -CH2-CHO group at C2 (ortho positions). Step 2 - Reaction with NaBH4 to give (A): NaBH4 is a mild reducing agent that selectively reduces aldehydes and ketones but does NOT reduce carboxylic acids. Therefore, NaBH4 reduces the aldehyde (-CHO) to a primary alcohol (-CH2OH). The carboxylic acid remains intact. Compound (A) is thus 2-(2-hydroxyethyl)benzoic acid: a benzene ring with -CO2H at C1 and -CH2CH2OH at C2. Step 3 - Reaction of (A) with H+ and heat (delta) to give cyclic (B): Under acidic conditions with heat, an intramolecular esterification (lactonization) occurs between the -CO2H group and the -OH group. The -CH2CH2OH chain has two carbons between the benzene ring and the OH. The carboxylic acid carbon plus the two-carbon chain (-CH2-CH2-OH) forms a six-membered lactone ring (delta-lactone) fused to the benzene ring. This product is 3,4-dihydroisocoumarin (isochroman-1-one): a benzene ring fused to a six-membered ring containing -O-C(=O)- with two CH2 groups. This corresponds to option (a). Step 4 - Why not (c): Option (c) shows a five-membered lactone (phthalide/isobenzofuranone). This would require only one carbon between the ring and the OH (i.e., -CH2OH directly on the ring), but in compound (A) there are two carbons (-CH2CH2OH), so a six-membered ring forms preferentially, not a five-membered ring. Step 5 - Why not (b): Option (b) is compound (A) itself (the open-chain hydroxy acid), not a cyclic product. Step 6 - Why not (d): Since only (a) is correct, (d) is wrong. Therefore, the correct answer is A.