Explain the mechanism of addition of HCN to a carbonyl group in presence of a base.

Explanation

(i) `HCN+OH^(-) hArr CN_(-) +H_(2)O`

Detailed Answer:
The mechanism of addition of HCN to carbonyl group takes places according to the following steps.
Step- (1): Addition of nucleophilic `(CN^(-))` to carbonyl carbon.
The nucleophilic attacks the `sp^(2)` hybridised carbonyl carbon atom forming tetrahedral alkoxide intermediate product.

Step- (2): Addition of proton of alkoxide ion.
Alkoxide ion intermediate product picks up a proton from the reaction medium to form the electrically neutral final product.