See image — Reaction Mechanism Chemistry Question

💡 Solution & Explanation

Concept: Grignard reagents react with esters in a two-step addition process. When 2 moles of a Grignard reagent react with an ester, the first mole attacks the carbonyl of the ester, expelling the alkoxy group to form a ketone intermediate, and the second mole adds to this ketone to give a tertiary alcohol after hydrolysis. Step 1: Identify the ester. Methyl butanoate is C3H7COOCH3 (butanoyl group = C3H7CO-, with methoxy as the leaving group). Step 2: First mole of CH3MgBr attacks the carbonyl carbon of methyl butanoate. The methoxy group (OCH3) is expelled as a leaving group, forming a ketone intermediate: C3H7COCH3 (methyl propyl ketone, i.e., 2-butanone extended: actually C3H7COCH3 = pentan-2-one... more precisely butanone with propyl: C3H7CO- + CH3 = C3H7COCH3). Step 3: The second mole of CH3MgBr adds to the ketone intermediate C3H7COCH3. The Grignard adds to the carbonyl carbon, placing another CH3 group on the carbonyl carbon. Step 4: After hydrolysis (H3O+/H2O), the magnesium alkoxide is protonated to give a tertiary alcohol: C3H7C(OH)(CH3)2. This is a tertiary alcohol where the central carbon bears the propyl group (C3H7), two methyl groups (from the original ester methyl and the second Grignard methyl), and an OH group. Why other options fail: - (a) C3H7COCH3 is only the ketone intermediate formed after the first Grignard addition; with 2 moles present, reaction proceeds further. - (c) C3H7CHOHCH3 would be a secondary alcohol, which would result from a Grignard reacting with an aldehyde, not consistent here. - (d) C3H7COCH(CH3)2 is a ketone product, not an alcohol; this does not result from this reaction sequence. Therefore, the correct answer is B.