See image — Reaction Mechanism Chemistry Question

💡 Solution & Explanation

Step 1 - Identify the target molecule: 2-phenyl-2-butanol is a tertiary alcohol with the structure CH3CH2C(OH)(Ph)CH3. The carbon bearing the OH group (C2) is bonded to: a phenyl group (Ph), an ethyl group (CH3CH2-), a methyl group (CH3), and OH. Step 2 - Grignard reactions with ketones/aldehydes: A Grignard reagent (R-MgX) acts as a nucleophile (carbanion equivalent) and attacks the carbonyl carbon of a ketone or aldehyde. The carbon of the Grignard becomes bonded to the carbonyl carbon, and after aqueous workup, an alcohol is formed. Step 3 - Retrosynthetic analysis of 2-phenyl-2-butanol: The C2 carbon has three carbon substituents: Ph, CH2CH3, and CH3. We can disconnect any one C-C bond at C2 to generate a Grignard + carbonyl pair: - Disconnect C2-CH2CH3: gives CH3CH2MgBr + PhC(=O)CH3 (methyl phenyl ketone = acetophenone with Ph) - Disconnect C2-CH3: gives CH3MgX + PhC(=O)CH2CH3 - Disconnect C2-Ph: gives PhMgX + CH3C(=O)CH2CH3 (methyl ethyl ketone) Step 4 - Evaluate option (a): CH3CH2MgBr + Ph-C(=O)-CH3. The Grignard (ethyl) attacks the carbonyl carbon of phenyl methyl ketone (acetophenone). The product after workup is: Ph-C(OH)(CH2CH3)(CH3) = 2-phenyl-2-butanol. This is correct. Step 5 - Evaluate option (b): CH3CH2MgBr + C6H5CH2C(=O)H. This is phenylacetaldehyde (PhCH2CHO). Attack by ethyl Grignard gives PhCH2CH(OH)CH2CH3, which is 1-phenyl-2-butanol, not 2-phenyl-2-butanol. Incorrect. Step 6 - Evaluate option (c): CH3MgI + C6H5CH2C(=O)CH3. The ketone is phenylacetone (PhCH2COCH3). Attack by methyl Grignard gives PhCH2C(OH)(CH3)2, which is 2-methyl-1-phenyl-2-propanol, not 2-phenyl-2-butanol. Incorrect. Step 7 - Evaluate option (d): C6H5MgCl + CH3C(=O)CH2CH2CH3. The ketone is 2-pentanone (methyl propyl ketone). Attack by phenyl Grignard gives Ph-C(OH)(CH3)(CH2CH2CH3) = 2-phenyl-2-pentanol, not 2-phenyl-2-butanol. Incorrect. Therefore, the correct answer is A.