See image — Reaction Mechanism Chemistry Question

💡 Solution & Explanation

Concept: Grignard reagents react with carbonyl compounds (ketones, aldehydes, esters, epoxides, CO2) to give alcohols after aqueous workup. To synthesize t-butyl alcohol [(CH3)3COH], we need a tertiary alcohol with the structure where a central carbon bears three methyl groups and one hydroxyl group. Step 1: Identify the target molecule. t-Butyl alcohol is (CH3)3C-OH, a tertiary alcohol with four carbons total: one central carbon bonded to three methyl groups and one OH. Step 2: Retrosynthetic analysis for a Grignard approach. A tertiary alcohol from a Grignard reaction is best made by reacting a Grignard reagent with a ketone. The disconnection of (CH3)3COH gives: CH3MgBr (Grignard) + (CH3)2C=O (acetone, dimethyl ketone). When CH3MgBr attacks the carbonyl carbon of acetone [CH3-C(=O)-CH3], it forms the alkoxide (CH3)3C-O-MgBr, which upon acidic workup (H3O+) gives (CH3)3COH = t-butyl alcohol. Step 3: Evaluate option (c). CH3MgBr + CH3-C(=O)-CH3 (acetone) in Et2O, then H3O+. CH3MgBr adds to the carbonyl of acetone: the methyl carbanion attacks the carbonyl carbon (which already has two methyl groups), producing a tetrahedral intermediate that after protonation gives (CH3)3COH. This is exactly t-butyl alcohol. This is the correct synthesis. Step 4: Evaluate other options and why they fail. - Option (a): CH3CH2MgBr + ethylene oxide → after workup gives a primary alcohol, CH3CH2CH2CH2OH (1-butanol), not t-butyl alcohol. - Option (b): CH3CH2CH2MgBr + CO2 → after workup gives a carboxylic acid, CH3CH2CH2COOH (butanoic acid), not an alcohol at all. - Option (d): CH3CH2MgBr + CH3CHO (acetaldehyde) → after workup gives CH3CH2CH(OH)CH3 (2-butanol), a secondary alcohol, not t-butyl alcohol. Therefore, the correct answer is C.