See image — Reaction Mechanism Chemistry Question

💡 Solution & Explanation

Step 1 - Identify product A from Reaction 1: PhMgBr (phenyl Grignard) reacts with CH3CN (acetonitrile). A Grignard reagent adds to a nitrile to give, after hydrolysis (H3O+), a ketone. Specifically, PhMgBr adds to the carbon of CH3CN to form an imine salt intermediate; upon aqueous acid workup (H3O+), this hydrolyzes to a ketone: Ph-C(=O)-CH3 (acetophenone). This is product A from Reaction 1. Step 2 - Verify product A from Reaction 2: Ph-C(=O)-OH is benzoic acid. Treatment with excess CH3Li (two equivalents): The first equivalent of CH3Li deprotonates the carboxylic acid (acting as a base) to give the carboxylate salt Ph-COO^- Li^+. The second equivalent of CH3Li adds to the carboxylate as a nucleophile to give, after aqueous workup (H3O+), a ketone: Ph-C(=O)-CH3 (acetophenone). Excess organolithium with carboxylic acids gives methyl ketones because the carboxylate intermediate resists a second addition under normal conditions (the dianion intermediate collapses to ketone on workup). Step 3 - Both reactions give Ph-C(=O)-CH3 (acetophenone): Reaction 1: PhMgBr + CH3CN -> [H3O+] -> Ph-CO-CH3 Reaction 2: PhCOOH + excess CH3Li -> [H3O+] -> Ph-CO-CH3 Both yield acetophenone, which is Ph-C(=O)-CH3. Step 4 - Why other options fail: (a) Ph-C(OH)(CH3)2 is 2-phenyl-2-propanol (tertiary alcohol) - this would require excess Grignard adding twice to a ketone, but that is not what happens here. (b) Ph-CHO (benzaldehyde) - no methyl group is introduced in a way that gives an aldehyde. (d) Ph-CH2-CO2H (phenylacetic acid) - unrelated to these reaction pathways. Therefore, the correct answer is C.