Q44 / 180 · COMEDK 2023 (Evening Shift) · Chemistry
Select the strongest base from the given compounds:
[A] p- $\mathrm{NO}_2-\mathrm{C}_6 \mathrm{H}_4 \mathrm{NH}_2$
[B] $\mathrm{C}_6 \mathrm{H}_5-\mathrm{CH}_2-\mathrm{NH}_2$
[C] $\mathrm{m}-\mathrm{NO}_2-\mathrm{C}_6 \mathrm{H}_4 \mathrm{NH}_2$
[D] $\mathrm{C}_6 \mathrm{H}_5 \mathrm{NH}_2$
- A[A]
- Correct answerB[B]
- C[D]
- D[C]
Solution
The basicity of amines is determined by the availability of the lone pair of electrons on the nitrogen atom for protonation.
In p-nitroaniline [A] and m-nitroaniline [C], the $-\mathrm{NO}_2$ group is a strong electron-withdrawing group (EWG) that decreases the electron density on the nitrogen atom through both inductive (-I) and resonance (-M) effects, significantly reducing basicity compared to aniline [D].
In aniline [D], the lone pair of electrons on the nitrogen atom is in conjugation with the benzene ring, which decreases its availability for protonation.
In benzylamine [B], the $-\mathrm{NH}_2$ group is attached to a $-\mathrm{CH}_2-$ group, which is attached to the benzene ring. The $-\mathrm{CH}_2-$ group acts as an insulator, preventing the lone pair of electrons on the nitrogen from being delocalized into the benzene ring via resonance. Consequently, benzylamine behaves like an aliphatic amine and is significantly more basic than aniline and its derivatives.
Answer: [B]
In p-nitroaniline [A] and m-nitroaniline [C], the $-\mathrm{NO}_2$ group is a strong electron-withdrawing group (EWG) that decreases the electron density on the nitrogen atom through both inductive (-I) and resonance (-M) effects, significantly reducing basicity compared to aniline [D].
In aniline [D], the lone pair of electrons on the nitrogen atom is in conjugation with the benzene ring, which decreases its availability for protonation.
In benzylamine [B], the $-\mathrm{NH}_2$ group is attached to a $-\mathrm{CH}_2-$ group, which is attached to the benzene ring. The $-\mathrm{CH}_2-$ group acts as an insulator, preventing the lone pair of electrons on the nitrogen from being delocalized into the benzene ring via resonance. Consequently, benzylamine behaves like an aliphatic amine and is significantly more basic than aniline and its derivatives.
Answer: [B]
Hence, the correct answer is option: 'B'.