See image — Aldehydes Ketones and Carboxylic Acids Chemistry Question

💡 Solution & Explanation

Concept: Cyanohydrin formation (Kiliani synthesis step) on an aldehyde bearing one chiral center creates a new chiral center at the former carbonyl carbon, giving two possible diastereomers. Step 1 – Identify the starting material. D-(+)-Glyceraldehyde is a chiral aldehyde with one stereocentre (C2, R configuration). Its Fischer projection shows H on the left and OH on the right at C2, with CHO at top and CH2OH at bottom. Step 2 – Reaction with KCN followed by H+. CN- acts as a nucleophile attacking the re or si face of the aldehyde carbonyl (C1). This creates a new stereocentre at C1 (formerly the carbonyl carbon), generating a cyanohydrin. After hydrolysis (H+), a 2-hydroxy acid (glyceric acid derivative, i.e., a tetrose precursor or threose/erythrose chain as cyanohydrin) is formed. Step 3 – Stereochemical outcome. Because CN- can attack either face of the planar carbonyl, two products are formed: one where the new OH at C1 is on the same side as C2-OH (syn addition → one diastereomer) and one where it is on the opposite side (anti addition → another deavdiastereomer). Both products retain the original chiral centre at C2 unchanged (it is not inverted). The two products are NOT mirror images of each other (because C2 is fixed in the R configuration in both), so they are diastereomers, not enantiomers. Step 4 – Why not the other options? - Racemic (b): A racemic mixture consists of equal amounts of enantiomers. The two products here are NOT enantiomers because C2 has the same absolute configuration in both; they differ only at C1. So the mixture is diastereomeric, not racemic. - Meso (c): A meso compound requires an internal plane of symmetry. The products here do not have the structural symmetry required for a meso compound (they have two different stereocentres, CHO-end OH vs. CHOH-CH2OH, with no internal mirror plane). - Optically pure enantiomer (d): Only one face would need to be exclusively attacked for an optically pure product. Since attack is non-selective (no chiral catalyst), both faces are attacked and a mixture is obtained, ruling this out. Step 5 – Conclusion. The two cyanohydrin (and subsequently hydroxy acid) products formed are diastereomers of each other (e.g., analogous to erythrose and threose in the Kiliani synthesis of glucose). Therefore, the correct answer is A.