JEE Main · 2025 · 24 Jan 2025 · Shift 2 · Haloalkanes and Haloarenes

Silver cyanide is a covalent salt in which the softer carbon end of the ambident $\mathrm{C}{\mathrm{N}}^{-}$ ligand is already bonded to silver, so when it reacts with an alkyl halide the nucleophile attacks through carbon, giving the isocyanide (isonitrile) as the major product. This is the standard contrast with potassium cyanide: KCN, being ionic, reacts through the harder nitrogen end and gives the nitrile instead.

The aryl carbon–halogen bonds on the ring (the $-\mathrm{Br}$ and $-\mathrm{I}$ substituents) do not undergo nucleophilic substitution under these conditions, since aryl halides resist $S_{N}2$ attack. Only the reactive benzylic $-\mathrm{C}{\mathrm{H}}_2\mathrm{Cl}$ is displaced.

The major product therefore retains the bromo and iodo substituents on the ring, with the benzylic chloride converted to $-\mathrm{C}{\mathrm{H}}_2-\mathrm{NC}$.