• The carbonyl group -C=O, in aldehydes and ketones is?polarised
• The oxygen atom is more?electronegative?than carbon drawing electron density towards itself
• This leaves the carbon atom?slightly?positively?charged?and the oxygen atom?slightly?negatively?charged
• The carbonyl carbon is therefore susceptible to attack by a?nucleophile, such as the cyanide ion

Nucleophilic addition

• The nucleophilic addition of hydrogen cyanide to carbonyl compounds is a two-step process
• In?step 1?the cyanide ion attacks the carbonyl carbon to form a negatively charged intermediate
• In?step 2?the negatively charged oxygen atom in the reactive intermediate quickly reacts with aqueous H+?(either from HCN, water or dilute acid) to form 2-hydroxynitrile

The cyanide ion attacks the carbonyl carbon to form a negatively charged intermediate which quickly reacts with a proton to form a 2-hydroxynitrile compound