Alkyl halides give alkyl cyanides with KCN but alkyl isocyanides with AgCN. Explain.
Answer : In cyanide ion, both carbon and nitrogen atoms have a pair of electrons; therefore, reaction can take place either through carbon or through nitrogen.
Potassium cyanide (KCN) is predominantly ionic, and gives cyanide ion on solution. Although both carbon and nitrogen atoms can donate electrons, reaction takes place through carbon atom since C−C bond is stronger than C−N bond.
Silver cyanide (AgCN), on the other hand, is predominantly covalent. Therefore, only nitrogen electron pair is available for bond formation. As a result, alkyl isocyanides are obtained as major products.
Ambident nucleophiles : In cyanide ion, both carbon and nitrogen atoms are electron donors. Such nucleophiles that have more than one one site through which reaction can take place are known as ambident nucleophiles.