Compounds Containing Nitrogen — JEE Advanced · 2020 · 27 Sep 2020 · Paper 2 Question with Solution

Consider the following four compounds I, II, III, and IV.

Choose the correct statement(s).

(A)The order of basicity is II $> I >$ III $>$ IV.
(B)The magnitude of $p K_{b}$ difference between I and II is more than that between III and IV.
(C)Resonance effect is more in III than in IV.✓ Correct
(D)Steric effect makes compound IV more basic than III.✓ Correct

Answer: (C), (D)

Solution

The compounds are:

I: Aniline ( $C_{6} H_{5} NH_{2}$ )
II: N,N-Dimethylaniline ( $C_{6} H_{5} N (CH_{3})_{2}$ )
III: 2,4,6-Trinitroaniline
IV: N,N-Dimethyl-2,4,6-trinitroaniline

Basicity order: II > I > IV > III

(A) Incorrect — actual order is II > I > IV > III ✗

(B)

p K_{b}

difference between I and II ≈ 0.53, while between III and IV ≈ 4.6. So the difference is greater for III and IV. ✗

(C) In III (2,4,6-trinitroaniline), the lone pair on nitrogen is strongly delocalized into the benzene ring due to strong -R effect of

- NO_{2}

groups. Resonance is more effective in III. ✓

(D) In IV, the two methyl groups cause steric inhibition of resonance (SIR) — the nitrogen lone pair is twisted out of the plane of the benzene ring, making it more available for protonation. Hence IV is more basic than III. ✓

Correct: (C), (D)

JEE Advanced · 2020 · 27 Sep 2020 · Paper 2 · One or more correct options

JEE Advanced · 2020 · 27 Sep 2020 · Paper 2 · Compounds Containing Nitrogen

Solution

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