See image — Reaction Mechanism Chemistry Question

💡 Solution & Explanation

Concept: The Hoffmann bromamide (Hofmann rearrangement) reaction requires a primary amide (R-CO-NH2) as the starting material. The reaction involves treatment of a primary amide with Br2 in alkaline (NaOH) solution, forming an N-bromoamide intermediate, which then undergoes rearrangement to give a primary amine with one fewer carbon. Step 1 - Identify the requirement: The substrate must be a primary amide, i.e., it must have a free -NH2 group attached to the carbonyl carbon (R-CO-NH2). This allows bromination at nitrogen followed by rearrangement. Step 2 - Analyze each option: (a) CH3-CO-NH2: This is acetamide, a primary amide. It has -NH2 and can undergo Hofmann bromamide reaction. ✓ (b) Ph-CO-NH2: This is benzamide, a primary amide. It has -NH2 and can undergo Hofmann bromamide reaction. ✓ (c) CH3-CO-NH-Br: This is N-bromoacetamide, which is itself the N-bromo intermediate formed in the Hofmann reaction. It can proceed through the rearrangement steps and effectively give the Hofmann reaction product. ✓ (d) Ph-CO-NH-Ph: This is N-phenylbenzamide (a secondary amide / dianilide). It does NOT have a free -NH2 group; the nitrogen already bears two substituents (one H replaced by Ph). There is no N-H available for the required N-bromination in the classic Hofmann sense, and crucially it is not a primary amide, so it cannot undergo the Hofmann bromamide rearrangement. Step 3 - Conclusion: Option (d) Ph-CO-NH-Ph is a secondary amide (N-phenylamide) and lacks the primary amide (-NH2) functionality required for the Hofmann bromamide reaction. Therefore, the correct answer is D.