See image — Aldehydes Ketones and Carboxylic Acids Chemistry Question

💡 Solution & Explanation

Concept: Grignard reagents (RMgX) act as nucleophiles and attack electrophilic carbonyl or epoxide carbons. To obtain a tertiary alcohol, the product carbon bearing the -OH group must be bonded to three carbon substituents. Step 1 - Analyze option (b) C2H5CO2CH3 (ethyl methyl ester / methyl propanoate): An ester reacts with excess Grignard reagent in two stages. First equivalent of CH3MgBr attacks the ester carbonyl, displacing -OCH3 to form a ketone intermediate (C2H5COCH3, methyl ethyl ketone). The ketone intermediate cannot escape the reaction mixture before the second equivalent of CH3MgBr attacks again. Second equivalent of CH3MgBr adds to the ketone, giving after hydrolysis: C2H5C(CH3)2OH, which is 2-methyl-2-butanol — a tertiary alcohol (the carbon bearing OH is bonded to C2H5, CH3, and CH3 — three carbon groups). Step 2 - Analyze why other options fail: (a) C2H5CHO (propanal, an aldehyde): One equivalent of CH3MgBr adds to give C2H5CH(OH)CH3 after hydrolysis — a secondary alcohol, not tertiary. (c) C2H5COOH (propanoic acid): The acidic proton first reacts with CH3MgBr to destroy one equivalent (forming CH4 gas). The carboxylate salt formed is unreactive to further Grignard addition under normal conditions, so no clean tertiary alcohol is obtained. (d) 2,3-dimethyloxirane (epoxide): CH3MgBr opens the epoxide to give a secondary alcohol (CH3CH(OH)CH(CH3)2 type product) — not tertiary. Step 3 - Conclusion: Only the ester (option b) reacts with two equivalents of CH3MgBr to reliably produce a tertiary alcohol. Therefore, the correct answer is B.