Arrange the following anilines in decreasing order of basicity 1 . C 6 H 5 N H 2 2 . o - C H 3 C 6 H 4 N H 2 3 . m - C H 3 C 6 H 4 N H 2 4 . p - C H 3 C 6 H 4 N H 2

Step-by-step solution

- C H 3 group is inductively electron-donating and base-strengthening from all position. Moreover, if - C H 3 is attached to benzene ring (or if R has benzylic H), it is electron-donating by hyper-conjugation from the ortho and para positions. Because of ortho effect, o-substituted aniline become less basic than aniline. Thus, p - C H 3 C 6 H 4 N H 2 (hyper-conjugation and induction) > m - C H 3 C 6 H 4 N H 2 (induction) > C 6 H 5 N H 2 > o - C H 3 C 6 H 4 N H 2 (ortho effect).