Complete the following reaction. Cyclohexanone $[A]$ reacts with $\mathrm{HCN}$ to give $[B]$, which on treatment with conc. $\mathrm{H}{}_2\mathrm{SO}{}_4$/heat gives $[C]$. $C$ is:

Solution & Explanation

\textbf{Answer:} (D) cyclohexane carboxylic acid \textbf{Solution:} Cyclohexanone ($A$) undergoes nucleophilic addition of $\mathrm{HCN}$ to give the cyanohydrin 1-hydroxycyclohexane-1-carbonitrile ($B$, ring bearing $-\mathrm{OH}$ and $-\mathrm{CN}$). On heating with conc. $\mathrm{H}{}_2\mathrm{SO}{}_4$, the nitrile group is hydrolysed (with loss of the alpha-hydroxy group) to give cyclohexane carboxylic acid ($C$, ring bearing $-\mathrm{COOH}$).