Arrange the following anilines in decreasing order of basicity 1. $ \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2} $ 2. o- $ \mathrm{CH}_{3} \mathrm{C}_{6} \mathrm{H}_{4} \mathrm{NH}_{2} $ 3. $ \mathrm{m}-\mathrm{CH}_{3} \mathrm{C}_{6} \mathrm{H}_{4} \mathrm{NH}_{2} $ 4. $ \mathrm{p}-\mathrm{CH}_{3} \mathrm{C}_{6} \mathrm{H}_{4} \mathrm{NH}_{2} $

Question

Arrange the following anilines in decreasing order of basicity 1. $ \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2} $ 2. o- $ \mathrm{CH}_{3} \mathrm{C}_{6} \mathrm{H}_{4} \mathrm{NH}_{2} $ 3. $ \mathrm{m}-\mathrm{CH}_{3} \mathrm{C}_{6} \mathrm{H}_{4} \mathrm{NH}_{2} $ 4. $ \mathrm{p}-\mathrm{CH}_{3} \mathrm{C}_{6} \mathrm{H}_{4} \mathrm{NH}_{2} $, $ 4>1>2>3 $, $ 4>3>1>2 $, $ 1>2>3>4 $, $ 4>3>2>1 $

MARKS App · Accepted Answer

- 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).

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