See image — Reaction Mechanism Chemistry Question

💡 Solution & Explanation

Concept: The Hoffmann bromamide (Hofmann rearrangement) reaction converts a primary amide (RCONH2) to a primary amine (RNH2) with one fewer carbon, via an isocyanate intermediate. The reagent is Br2/KOH. Step 1: Identify the substrate. The starting material is Ph-CH(OH)-C(=O)-NH2, an alpha-hydroxy amide. The amide group is -C(=O)-NH2, and the R group attached to the carbonyl is Ph-CH(OH)-. Step 2: Apply Hofmann rearrangement. In the Hofmann rearrangement, the amide RCONH2 loses the carbonyl carbon as CO2 (via an isocyanate R-N=C=O intermediate that hydrolyzes), giving the amine R-NH2. Here R = Ph-CH(OH)-, so the amine formed would be Ph-CH(OH)-NH2. Step 3: However, Ph-CH(OH)-NH2 is an alpha-amino alcohol (a gem-amino alcohol on the benzylic position). Under the strongly basic aqueous conditions (KOH, heat), Ph-CH(OH)-NH2 is unstable and undergoes elimination or tautomerism. Actually, Ph-CH(OH)-NH2 is an aminol, which is the hydrated form of an imine/aldehyde. An aminol Ph-CH(OH)-NH2 readily loses NH3 (ammonia) to give Ph-CHO (benzaldehyde). Step 4: Therefore, the net product of the Hofmann rearrangement on Ph-CH(OH)-CONH2 is Ph-CHO (benzaldehyde), because the initially formed alpha-hydroxy amine Ph-CH(OH)-NH2 spontaneously loses NH3 under the reaction conditions to give the aldehyde. Why other options fail: - (a) Ph-C(=O)-CH3 (acetophenone): This would require a different carbon skeleton and no loss of the carbonyl carbon. - (c) Ph-CH(OH)(NO2): There is no source of NO2 in the reaction. - (d) Ph-CH2-NH2 (benzylamine): This would require reduction of the OH group and retention of the amine, which does not occur here. Therefore, the correct answer is B.