Propose a mechanism for each cyanohydrin synthesis just shown.

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

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.