See image — Alcohols Phenols and Ethers Chemistry Question

💡 Solution & Explanation

Concept: In dilute HCl, an amide bond can undergo acid-catalyzed hydrolysis. However, here the question asks about conversion to a constitutional isomer, meaning the molecular formula stays the same but connectivity changes. Step 1: Identify compound A. Compound A is a trans-1,2-disubstituted cyclopentane with: - C1 bearing an -OH group - C2 bearing an -NH-C(=O)-Ar group (where Ar = p-nitrophenyl) This is an amide with a free hydroxyl group on the adjacent carbon. Step 2: Understand the reaction with dil. HCl. In dilute HCl, the hydroxyl group and the amide nitrogen can participate in an intramolecular or intermolecular rearrangement. The key transformation here is an O-to-N acyl migration (or N-to-O acyl migration). Specifically, the acyl group migrates from nitrogen to oxygen: the -OH attacks the carbonyl of the amide intramolecularly, and the nitrogen leaves, converting the amide (-NH-C(=O)-Ar) into an ester (-O-C(=O)-Ar) while releasing -NH2. This is an O-acyl migration where the hydroxyl oxygen displaces the amine nitrogen at the carbonyl carbon. Step 3: Product identification. After N-to-O acyl migration: - The NH group becomes a free NH2 on the cyclopentane ring - The OH oxygen becomes the ester oxygen: -O-C(=O)-Ar - Result: cyclopentane ring with NH2 on one carbon and O-C(=O)-C6H4-NO2(para) on the adjacent carbon This matches option (a): cyclopentane with NH2 substituent and ester -O-C(=O)-C6H4-NO2 (para). Step 4: Verify it is a constitutional isomer. Compound A (amide with OH): same molecular formula as compound B (amine with ester). Both have the same atoms connected differently — one is an amide+alcohol, the other is an amine+ester. These are constitutional isomers. ✓ Step 5: Why other options fail: - (b) and (c): Show a cyclopentene (unsaturated ring) and a different connectivity at the benzylic carbon with OH; these would require loss of H2O or other changes inconsistent with simple acyl migration. - (d): Shows a bicyclic orthoester-like structure which is not a simple constitutional isomer produced by acyl migration under mild acidic conditions. Therefore, the correct answer is A.