Arrange the following amines in the decreasing order of their basicity in aqueous phase.
A. C2H5NH2
B. C6H5NHCH3
C. (C2H5)2NH
D. C6H5NH2
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → C, A, B, D
An amine is basic because the lone pair on nitrogen can accept a proton. Two factors decide the order here:
Aliphatic versus aromatic: in an aryl amine, the nitrogen lone pair is delocalised into the benzene ring by resonance, so it is much less available. Every aliphatic amine is therefore a much stronger base than any aryl amine.
Alkyl groups (+I effect): alkyl groups push electrons towards nitrogen. In water, the ethyl amines follow 2° > 1°, because of the combined effect of induction, solvation and steric hindrance. On an aryl amine, an N-methyl group also raises basicity slightly.
Combining the two factors (a lower pKb means a stronger base):
\( \displaystyle \text{aliphatic }2^{\circ} > \text{aliphatic }1^{\circ} > \text{N-alkyl aryl amine} > \text{aryl amine} \)
Matching the given compounds:
(C) \( \ce{(C2H5)2NH} \): diethylamine (aliphatic 2°)
(A) \( \ce{C2H5NH2} \): ethanamine (aliphatic 1°)
(B) \( \ce{C6H5NHCH3} \): N-methylaniline (aryl, with an N-methyl group)
(D) \( \ce{C6H5NH2} \): aniline (aryl)
Shortcut: Diethylamine (C) is the strongest base and aniline (D) the weakest. Only Option (1) starts with C and ends with D.
NCERT (2026-27 edition):
Basic Character of Amines – …
