See image — Reaction Mechanism Chemistry Question

💡 Solution & Explanation

Concept: Grignard reagents (RMgX) are strong bases and nucleophiles. When they react with compounds that have acidic protons (active hydrogen atoms), they act as a base and abstract the proton, producing a hydrocarbon (R-H) and the corresponding magnesium salt. This reaction is called the 'active hydrogen' reaction. Step 1: Identify what constitutes an 'active hydrogen' compound. Any compound with an O-H, N-H, or S-H bond (or terminal alkyne C-H) will react with RMgX to produce a hydrocarbon. Step 2: Analyze option (a) CH3CH2OH (ethanol). Ethanol is an alcohol containing an O-H bond. The O-H proton is sufficiently acidic to react with the Grignard reagent (RMgX). The reaction proceeds as: RMgX + CH3CH2OH → R-H (hydrocarbon) + CH3CH2OMgX. The Grignard reagent abstracts the O-H proton, producing a hydrocarbon (R-H). Step 3: Analyze why the other options do not simply produce a hydrocarbon. Option (b) CH3CHO (acetaldehyde) contains no active O-H proton; the Grignard reagent acts as a nucleophile and adds to the carbonyl carbon, yielding a secondary alcohol after workup, not a hydrocarbon. Option (c) CH3COCH3 (acetone) similarly undergoes nucleophilic addition at the carbonyl, giving a tertiary alcohol after workup, not a hydrocarbon. Option (d) CH3CO2CH3 (methyl acetate) also undergoes nucleophilic addition-elimination at the ester carbonyl, not simple proton abstraction to give a hydrocarbon. Step 4: Conclude that only CH3CH2OH, which has an active O-H hydrogen, reacts with the Grignard reagent via a proton-transfer (acid-base) reaction to directly yield a hydrocarbon. Therefore, the correct answer is A.