All aliphatic amines are more basic than ammonia but due to delocalization of lone pair of electrons of the nitrogen atom on the benzene ring, aniline is a weaker base than ammonia. The basic strength of the substituted anilines, however, depends upon the nature of the substituent. Whereas electron-donating groups tend to increase, electron-withdrawing groups tend to decrease the basic strength. The base strengthening effect of the electron-donating groups and base weakening effect of the electron-withdrawing groups is, however ,more pronounced at p-than at m-position. However, due to ortho effect, o-substituted anilines are weaker bases than anilines regardless of the nature of substituent whether electron-donating or electron-withdrawing.
What is the order of basicity of
I. p-methylaniline
II. m-methylaniline
III, aniline
IV. o-methylaniline

Options

A. `I gt II gt III gt IV`
B. `I gt II gt IV gt III`
C. `IV gt I gt II gt III`
D. `II gt I gt IV gt III`

Answer

A

Explanation

Due to ortho-effect, o foluidíne is the weakest base even weaker than aniline. Since `CH_3` group is electron donating both by +I-effect and hyperconjugation effect, therefore, both m-toluidine and p-toluidine are stronger bases than aniline. However, a `CH_3` group cannot exert its hyperconjugation effect but can exert only its +I-effect from m-position. Therefore, m-toluidine is a weaker base thar prolidine.