Question

Propose a mechanism for each cyanohydrin synthesis just shown.

Short answer

The conjugate base of hydrogen cyanide (HCN) is cyanide ion (CN^-) . Cyanide ion is considered to be a strong base as well as a strong nucleophile also. Cynaide ion can attack carbonyl compounds (aldehydes and ketones) to form an additional product which is more commonly known as the cyanohydrins

Step-by-step solution

Cyanohydrins

The conjugate base of hydrogen cyanide (HCN) is cyanide ion (CN^-) . Cyanide ion is considered to be a strong base as well as a strong nucleophile also. Cynaide ion can attack carbonyl compounds (aldehydes and ketones) to form an additional product which is more commonly known as the cyanohydrins

Mechansim for the synthesis of each cyanohydrin

The formation of cyanohydrin is a type of base-catalyzed addition to a carbonyl group where a strong nucleophile (CN^-) adds in the first step to give an alkoxide which on protonation in the second step forms the cyanohydrin.

(propanol) (propanol cyanohydrin)

(butane-2-one) (butane-2-one cyanohydrin)

(di-tert-butylketone)

Ketones hindered by the presence of large alkyl groups usually react very slowly with hydrogen cyanide and give poor yields of cyanohydrins. Poor yield is due to steric effects.