The decreasing order of basicity of the following amines in aqueous solution is
(A) Ethylamine
(B) N-Ethylethanamine
(C) N,N-Diethylethanamine
(D) Benzenamine
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (B), (C), (A), (D)
An amine is basic because the lone pair on nitrogen accepts a proton. In water the basic strength of alkylamines is decided by three factors working together:
Inductive effect: alkyl groups push electrons towards nitrogen (+I), so on this count 3° > 2° > 1°.
Solvation of the ammonium ion: the more N–H hydrogens the cation has, the better it is stabilised by hydrogen bonding with water, so on this count 1° > 2° > 3°.
Steric hindrance: bulky ethyl groups crowd the nitrogen and hinder both protonation and solvation, which pulls the tertiary amine down.
For the ethyl amines the balance of these factors gives 2° > 3° > 1°. Aniline is much weaker than all of them, because its lone pair is delocalised into the benzene ring and is less available for a proton.
(A) Ethylamine: \( \ce{C2H5NH2} \), primary.
(B) N-Ethylethanamine: \( \ce{(C2H5)2NH} \), secondary.
(C) N,N-Diethylethanamine: \( \ce{(C2H5)3N} \), tertiary.
(D) Benzenamine: \( \ce{C6H5NH2} \), aromatic.
Shortcut: The secondary amine is the strongest base and aniline the weakest, so the order starts with (B) and ends with (D): Options (1) and (2). Since the tertiary ethylamine is stronger than the primary one, (C) comes before (A), which leaves Option (2).
NCERT (2026-27 edition):
Basic Character of Amines – “… The order of basic strength in case of methyl substituted amines and ethyl substituted amines in aqueous solution is as follows:
(C2H5)2NH > (C2H5)3N > C2H5NH2 > NH3”
Basic Character of Amines – “… Hence, the proton acceptability or the basic nature of aniline or other aromatic amines would be less than that of ammonia.”