Due to presence of electron withdrawing nitro group, delocalisation of lone pair of electron is improved. This effect observed in para and ortho position. In ortho position, very close inductive effect of nitro group is also observed. Hence, O-nitroaniline is less basic than p-nitroaniline. In m-nitroaniline, only inductive effect is present. Order of basicity is as follows: aniline >m-nitroaniline >p-nitroaniline >O-nitroaniline.