Q45 / 71 · NTA Abhyas (JEE Main) 2020 · Chemistry · Amines

Arrange the following anilines in decreasing order of basicity

1. C6H5NH2

2. o-CH3C6H4NH2

3. m-CH3C6H4NH2

4. p-CH3C6H4NH2

  • A
    4 > 1 > 2 > 3
  • Correct answer
    B
    4 > 3 > 1 > 2
  • C
    1 > 2 > 3 > 4
  • D
    4 > 3 > 2 > 1

Solution

-CH3 group is inductively electron-donating and base-strengthening from all position. Moreover, if -CH3 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-CH3C6H4NH2 (hyper-conjugation and induction) > m-CH3C6H4NH2 (induction) > C6H5NH2>o-CH3C6H4NH2 (ortho effect).

Hence, the correct answer is option: 'B'.

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