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.
Among the following, the weakest base is

Options

A. `C_6 H_5 NH_2`
B. `p-CH_3 O-C_6 H_4 NH_2`
C. `m-CH_3 O-C_6 H_4 NH_2`
D. `o-CH_3 O - C_6 H_4 NH_2`

Answer

C

Explanation

When `-OCH_3` group is present at m-position, it can exert only its -I-effect since resonance effect does not operate at m-position. This decreases the electron density on the nitrogen atom to such an exten that m-methoxyaniline (m-anisidine) becomes a weaker base than aniline even weaker than o-methoxyaniline .