What product would you expect to obtain when reacting ethanal (or acetaldehyde) with potassium cyanide (KCN) in dilute acid? Draw a curly arrow mechanism for this transformation, and determine whether you obtain one enantiomer or a racemic mixture.

The product obtained is a cyanohydrin, with the formula CH3CH(OH)(CN) where the cyanide anion has acted as a nucleophile towards the aldehyde. The mechanism would first show the lone pair on the carbonyl oxygen becoming protonated by the acid, putting a positive charge on the oxygen. This makes the carbonyl carbon more electrophilic, so the next step is to show the lone pair on the carbon of the cyanide anion attacking the carbonyl carbon, pushing the electrons up to the carbonyl oxygen, quenching the positive charge. This forms the desired cyanohydrin.This process forms a stereogenic centre, where there are 4 different substituents on one carbon. However, as the cyanide anion can attack from either face of the carbonyl, a racemic mixture will form.