Chemistry - GOC Question with Solution | TestHub

In 4-chlorobenzylamine the $\mathrm{N}{\mathrm{H}}_2$ group is separated from the ring by a $\mathrm{C}{\mathrm{H}}_2$, so its lone pair is fully available (conjugate acid $\mathrm{p}{K}_{\mathrm{a}}$ ≈ 9.3). In 4-chloroaniline and 4-nitroaniline the lone pair delocalises into the ring (pKaH ≈ 4 and ≈ 1), and in the amide the lone pair is tied up by the adjacent carbonyl (essentially non-basic). 4-Chlorobenzylamine is the most basic.