Reaction of an alkyl halide with KCN and AgCN gives different products ? Explain.

Explanation

KCN is predominately ionic and therefore both C and N atoms are free to donate electron pair. Since C -C bond is relatively stronger than C -N bond, the attack occurs mostly through the carbon atom of the cyanide group forming alkyl cyanides as the major products.
`K^(+) - bar(C)N + R^(delta-) to underset("Alkyleyanide") (R -C -= N + K^(+) X^(-))`
On the other hand AgCN is predominately covalent. Therefore in this case only Nitrogen atom is free to donate electron pair and the attack mostly occurs through the N-atom of the cyanide group forming alkyl isocyanide as the major products.
`Ag - C^(-) -= N: + R^(delta+) - X^(delta-) to underset("alkylisocyanide")(R - N^(+) -= C^(-) + AgX)`