See image — Reaction Mechanism Chemistry Question

💡 Solution & Explanation

Concept: Reaction of a nitrile with a Grignard reagent followed by aqueous acid workup. Step 1: The Grignard reagent CH3MgI acts as a nucleophile. The methyl carbanion (CH3-) attacks the electrophilic carbon of the nitrile (C≡N) in CH3CN (acetonitrile). This addition gives an imine salt (metallated imine): CH3-C(=NMgI)-CH3. Step 2: Upon aqueous acid workup (H3O+), the metal is replaced by a proton, giving an imine (aldimine/ketimine): CH3-C(=NH)-CH3. This is the primary product immediately after hydrolysis of the metal-nitrogen bond. Step 3: Under mild aqueous acid conditions (H3O+), the imine can hydrolyze further to a ketone. The imine CH3-C(=NH)-CH3 hydrolyzes to give CH3-C(=O)-CH3 (acetone, a ketone) plus NH3. This is the major isolable product because imines readily hydrolyze under the acidic aqueous workup conditions used. Why other options fail: - (a) CH3-CH2-NH-CH3: This would be a secondary amine, which would require reduction conditions (e.g., LiAlH4), not Grignard addition. - (b) CH3-C(=NH)-CH3: This is the intermediate imine formed initially, but it hydrolyzes under H3O+ workup to give the ketone; it is not the major isolated product. - (d) CH3-CH2-COOH: A carboxylic acid would result from a different reaction pathway (e.g., Grignard addition to CO2), not from nitrile + CH3MgI. The overall transformation is: nitrile + RMgX → (after H3O+ workup) → ketone. CH3CN + CH3MgI → CH3COCH3 (acetone). Therefore, the correct answer is C.