See image — Reaction Mechanism Chemistry Question

💡 Solution & Explanation

Step 1 - Identify the starting material: The structure shown is acetaldehyde (CH3CHO), a carbonyl compound with H and CH3 attached to the carbonyl carbon. Step 2 - Reaction with PhMgBr (Grignard reagent): The phenylmagnesium bromide acts as a nucleophile and attacks the carbonyl carbon of acetaldehyde. The carbonyl carbon is sp2 (planar, trigonal), so attack can occur from either the re-face or si-face with equal probability. Step 3 - Product identification: The product after protonation (H+) is 1-phenylethanol: Ph-CH(OH)-CH3. The carbon bearing OH, Ph, CH3, and H is a new stereocenter. Step 4 - Stereochemical outcome: Since acetaldehyde is achiral and the Grignard reagent (PhMgBr) is also achiral, there is no chiral influence to favor one face of attack over the other. Attack from the re-face and si-face are equally probable, yielding (R)- and (S)-1-phenylethanol in equal amounts (50:50 ratio). Step 5 - Classification of product mixture: A 50:50 mixture of two enantiomers is called a racemic mixture (racemate). Step 6 - Why other options fail: - (a) Diastereomers: Only one new stereocenter is created; diastereomers require at least two stereocenters with different configurations, so this does not apply. - (c) Pure enantiomer: This would require asymmetric induction, which is absent here since both reactants are achiral. - (d) Meso: A meso compound requires an internal plane of symmetry with multiple stereocenters; not applicable here. Therefore, the correct answer is B.