Question

Account for the following.

pK_b of aniline is more than that of methylamine.

Answer 1

In aniline, the lone pair of electrons on the N-atom is delocalized over the benzene ring. As a result electron density on the nitrogen decreases. In contrast in CH₃NH₂, the +I effect of CH₃ increases the electron density on the N-atom. Therefore, aniline is a weaker base than methylamine and hence its pK_b value is more than that of methyl amine.