Write the mechanism of the following reaction:
`nBuBr+KCN overset(EtOH-H_(2)O)(rarr)nBuCN`.

Explanation

KCN ionises in solution to form cyanide ion `(overset(color(red)(Theta))( :C)-=N: harr :C = underset( .. )overset(color(red)(Theta))(N): )`, which is an ambident nucleophile. It attacks through C-atom rather than N-atom, because carbon has more polarisable electron cloud owing to its larger size and lower electronegativity. Thus n-butyl cyanide is the predominant product. since, C-C bond is stronger than C-N bond, it favours the formation of this product.
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