Question

Isocyanide can be prepared from alkyl halide on treatment with

• A. $\text{AgCN}$
• B. $\text{AgNC}$
• C. $\text{KCN}$
• D. None of these

Answer 1

Answer: (A)

$R-X+KCN\to \underset{\begin{array}{c}\text{alkyl}\text{cyanide}\\ \text{(attack}\text{occurs}\text{through}\text{C)}\end{array}}{\mathrm{RCN}}$ $R-X+AgCN\to \underset{\begin{array}{c}\text{alkyl}\\ \text{isocyanide}\\ \text{(attack}\text{occurs}\text{through}\text{N)}\end{array}}{R-NC}$ $\text{AgCN}$ is predominantly covalent, therefore, in this case only N-atom is free to donate electron pair. Thus, the attack mostly occurs through the N-atom of the cyanide group forming alkyl isocyanides. $C{N}^{-}$ behaves as an ambidentate nucleophile.