See image — Aldehydes Ketones and Carboxylic Acids Chemistry Question

💡 Solution & Explanation

Concept: Acetal formation from an aldehyde or ketone reacting with a diol. Step 1: Examine the product. In the product, the CH2O (from the primary alcohol at C1) and the oxygen at C2 (secondary OH) have both reacted with a single carbon bearing a Ph group and one H, forming a 1,3-dioxolane-type cyclic acetal. The acetal carbon bears Ph and H, which means it came from an aldehyde R-CHO where R = Ph. Step 2: An acetal is formed when an aldehyde reacts with a 1,2-diol (or 1,3-diol). Here, the CH2OH at the top (C1) and the OH at C2 form a five-membered cyclic acetal with the aldehyde carbon, giving a -O-CH(Ph)-O- bridge. The acetal carbon has one H and one Ph substituent, consistent with benzaldehyde (PhCHO). Step 3: If the reagent were acetophenone (option a), the acetal carbon would bear Ph and CH3 (no H). If it were phenylacetaldehyde (option c) or phenylacetone (option d), the acetal carbon would bear Ph-CH2 rather than Ph directly. Only benzaldehyde (PhCHO) gives an acetal carbon bearing exactly Ph and H. Step 4: Why other options fail: - (a) Acetophenone would give acetal carbon with Ph and CH3, not Ph and H. - (c) Phenylacetaldehyde would give acetal carbon with Ph-CH2 and H. - (d) Phenylacetone would give acetal carbon with Ph-CH2 and CH3. Therefore, the correct answer is B.