Question

O-nitroaniline or p-nitroaniline which will be more basic?

Answer 1

p-nitroaniline is more basic than o-nitroaniline.

The nitro group is an electron withdrawing group. When attached on the benzene ring, it activates the ring by pulling the electrons towards itself. In ortho isomer, the -NO2 group is on the adjacent carbon atom. Therefore the lone pair on nitrogen atom travels from aniline into the ring to the nitro group and is thus stabilised by the electron withdrawing nature of nitro group. Hence the nitrogen atom acquires a double bond character ( due to +R effect) andN-H bond in NH2 becomes weak. Hence it is more acidic ( H+ ion can be easily given away since the bond weakens). On the other hand, in para isomer the distance between the NH2 group and NO2 group increases. Therefore the inductive effect is less pronounced.

Hence p-nitroaniline is more basic ( as it is less acidic) than o-nitroaniline.

Hope this helps u

Answer 2

Because inductive effect depends upon distance and therefore is dominant more at ortho position making Ortho nitro aniline more acidic and less basic