JEE Main · 2023 · 11 Apr 2023 · Shift 1 · Aldehydes Ketones and Carboxylic Acids

The substrate is a 2-alkylcyclohexanone. Hot $\mathrm{KMnO}{}_4$ oxidatively cleaves the ring at the carbon-carbon bond between the carbonyl carbon and the substituted $\alpha$-carbon: the original carbonyl carbon is oxidised to a carboxyl group while the $\mathrm{CHR}$ carbon is oxidised to a new ketonic carbonyl. This opens the ring to the keto-acid $\mathrm{R}-\mathrm{CO}-(\mathrm{CH}{}_2){}_4-\mathrm{COOH}$, which is A. Hydrazine with potassium hydroxide (Wolff-Kishner reduction) then converts only the ketonic $\mathrm{C}=\mathrm{O}$ to a $\mathrm{CH}{}_2$ group, leaving the carboxylic acid intact, after acidic work-up. Hence A is $\mathrm{R}-\mathrm{CO}-(\mathrm{CH}{}_2){}_4-\mathrm{COOH}$ and B is $\mathrm{R}-(\mathrm{CH}{}_2){}_5-\mathrm{COOH}$.