See image — Reaction Mechanism Chemistry Question

💡 Solution & Explanation

Step 1 – Identify product A from (C2H5O)2CO (diethyl carbonate) with excess CH3MgBr / H3O+. Diethyl carbonate is a carbonate ester with the structure (C2H5O)2C=O. When treated with excess Grignard reagent (CH3MgBr), the reaction proceeds in two stages: - First equivalent of CH3MgBr attacks the carbonyl to give, after loss of one ethoxy group, an ester intermediate (CH3C(=O)OC2H5, ethyl acetate). - A second equivalent of CH3MgBr attacks the ester carbonyl to give, after hydrolysis, a tertiary alcohol: (CH3)2C(OH)CH3, i.e., 2-methyl-2-propanol (tert-butanol), specifically CH3C(OH)(CH3)CH3 = 2-methyl-2-propanol. Wait – let us recount: diethyl carbonate + 2 CH3MgBr → after first addition and elimination of EtO⁻ gives ethyl acetate (CH3COOEt); ethyl acetate + 1 more CH3MgBr → after hydrolysis gives 2-methyl-2-propanol (tert-butanol, (CH3)3COH). So overall 2 equivalents of CH3MgBr are consumed. Product A = (CH3)3COH (2-methyl-2-propanol / tert-butanol). Step 2 – Check option (a): CH3CH2CHO (propanal) + CH3MgBr (2 mol) / H3O+. Propanal is an aldehyde; the first mole of CH3MgBr adds to give, after hydrolysis, a secondary alcohol CH3CH2CH(OH)CH3 (2-butanol). But an aldehyde only consumes one mole of Grignard per molecule (one carbonyl). The product is 2-butanol, not tert-butanol. Option (a) does NOT give product A. Step 3 – Check option (b): CH3C(=O)OC2H5 (ethyl acetate) + CH3MgBr (2 mol) / H3O+. Ethyl acetate is an ester. Two moles of CH3MgBr react: the first gives an intermediate (hemiketal-type tetrahedral intermediate) that collapses to a ketone (acetone, CH3COCH3), and then the second mole of CH3MgBr adds to acetone to give, after hydrolysis, (CH3)3COH (tert-butanol). Product = tert-butanol = A. Option (b) GIVES product A. Step 4 – Check option (c): CH3C(=O)CH3 (acetone) + CH3MgBr (1 mol) / H3O+. Acetone + one mole of CH3MgBr → after hydrolysis gives (CH3)3COH (tert-butanol). Product = tert-butanol = A. Option (c) GIVES product A. Step 5 – Evaluate the answer choices. Option (a) gives 2-butanol, not tert-butanol → incorrect. Option (b) gives tert-butanol → correct. Option (c) gives tert-butanol → correct. Option (d) states "as in (b) and (c)" → both (b) and (c) give product A → this is the correct answer. Therefore, the correct answer is D.