See image — Reaction Mechanism Chemistry Question

💡 Solution & Explanation

Step 1 - Identify the target alcohol. The target molecule is a tertiary alcohol with the structure: a central carbon bearing four substituents - Ph (phenyl), CH3 (methyl), CH2CH3 (ethyl), and OH. This is 2-phenyl-2-butanol... wait, let me re-examine: the carbon bears Ph, CH3, CH2CH3, and OH, making it 1-phenyl-1-methylpropan-1-ol (or equivalently, the carbon bonded to Ph, Me, Et, and OH). Step 2 - Understand the Grignard retrosynthesis. To form a tertiary alcohol via Grignard reaction with a ketone, we break one of the C-C bonds to the central carbon (not the C-OH bond). The central carbon has three carbon substituents: Ph, CH3, and Et. Each bond can be disconnected to give a Grignard reagent and a ketone: - Disconnect Ph: PhMgBr + ketone (CH3-C(=O)-Et = 2-butanone) --> target - Disconnect CH3: CH3MgBr + ketone (Ph-C(=O)-Et) --> target - Disconnect Et: EtMgBr + ketone (Ph-C(=O)-CH3 = acetophenone) --> target Step 3 - Evaluate each option. (a) PhMgBr + 2-butanone (CH3-CO-CH2CH3): PhMgBr attacks the carbonyl of 2-butanone, giving the carbon bonded to Ph, CH3, Et, and OH. This WORKS. Correct combination. (b) EtMgBr + Ph-C(=O)-CH3 (acetophenone): EtMgBr attacks acetophenone carbonyl, giving carbon bonded to Et, Ph, CH3, and OH. This WORKS. Correct combination. (c) CH3MgBr + Ph-C(=O)-Et (phenyl ethyl ketone): CH3MgBr attacks the carbonyl, giving carbon bonded to CH3, Ph, Et, and OH. This WORKS. Correct combination. (d) EtMgBr + Ph-C(=O)-CH2CH3 (phenyl ethyl ketone / propiophenone): EtMgBr attacks the carbonyl of Ph-CO-Et, giving a central carbon bonded to Et, Ph, Et, and OH - i.e., Ph-C(OH)(Et)(Et), which is 1-phenyl-1-ethylpropan-1-ol. This product has Ph, two ethyl groups, and OH on the central carbon - NOT the target alcohol (which requires Ph, CH3, and Et). This does NOT give the required alcohol. Step 4 - Conclusion. Option (d) cannot be used to prepare the given alcohol because EtMgBr reacting with Ph-C(=O)-CH2CH3 produces Ph-C(OH)(Et)2, not Ph-C(OH)(Me)(Et). Therefore, the correct answer is D.