JEE Advanced 2026 Paper 1, Chemistry Section 3 Q3: Carboxylic Acid Derivatives

Reaction (i). A β-keto acid loses CO${}_2$ on heating (decarboxylation). The given diacid has two β-keto carboxylic acid groups (each CO${}_2$H is β to the central ketone), so both decarboxylate to give pentan-3-one (CH${}_3$CH${}_2$–CO–CH${}_2$CH${}_3$). $\mathbf{X}$ contains 1 carbonyl group.

Reaction (ii). trans-3,4-dicarboxy-cyclopentanone has two adjacent –CO${}_2$H groups on neighbouring ring carbons. On heating, these undergo intramolecular dehydration to form a cyclic anhydride, fused to the unchanged cyclopentanone ring. The product $\mathbf{Y}$ is a bicyclic system containing one ring ketone (C=O) and two anhydride carbonyls (–CO–O–CO–), giving 3 carbonyl groups.

Sum = $1+3=4.00$.