JEE Main · 2022 · 25 Jun 2022 · Shift 2 · Aldehydes Ketones and Carboxylic Acids

Enamine formation requires the ketone to undergo nucleophilic addition of a secondary amine followed by elimination of water. This requires at least one α-hydrogen for the elimination step. More importantly, the carbonyl carbon must be accessible to nucleophilic attack. In option (C), the ketone has bulky tert-butyl groups on both sides of the carbonyl ($(\mathrm{CH}{}_3){}_3\mathrm{C}-\mathrm{CO}-\mathrm{C}(\mathrm{CH}{}_3){}_3$). This creates severe steric hindrance that prevents the secondary amine from approaching and attacking the carbonyl carbon. Therefore, this ketone will NOT form an enamine.