Identify the major product $C$ formed in the following reaction sequence: $\mathrm{CH}{}_3\mathrm{CH}{}_2\mathrm{CH}{}_2\mathrm{I}\stackrel{\mathrm{NaCN}}{\to }$ $A$ $\underset{\mathrm{OH}{}^{-}}{\overset{\text{partial hydrolysis}}{\to }}$ $B$ $\stackrel{\mathrm{NaOH}+\mathrm{Br}{}_2}{\to }$ $C$ (major)

Solution & Explanation

1-Iodopropane undergoes $\mathrm{S}{}_{\mathrm{N}}2$ substitution with $\mathrm{NaCN}$ to give butanenitrile $\mathrm{CH}{}_3\mathrm{CH}{}_2\mathrm{CH}{}_2\mathrm{CN}$ ($A$). Partial (controlled) hydrolysis stops at the amide butanamide $\mathrm{CH}{}_3\mathrm{CH}{}_2\mathrm{CH}{}_2\mathrm{CONH}{}_2$ ($B$). $\mathrm{NaOH}+\mathrm{Br}{}_2$ is the Hofmann bromamide degradation, which removes one carbon and converts the amide to the primary amine with one fewer carbon: propylamine $\mathrm{CH}{}_3\mathrm{CH}{}_2\mathrm{CH}{}_2\mathrm{NH}{}_2$ ($C$).