The decreasing order of basic strength of the following amines in aqueous solution is
(A) EtNH2
(B) NH3
(C) (Et)2NH
(D) (Et)3N
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (C), (D), (A), (B)
An amine is basic because the lone pair on nitrogen can accept a proton. In water, the basic strength of aliphatic amines is decided by three factors acting together:
Inductive effect (+I): alkyl groups push electrons towards nitrogen and make the lone pair more available. More alkyl groups mean a stronger effect: 3° > 2° > 1°.
Solvation (hydration): the protonated amine is stabilised by hydrogen bonding with water. The more N–H hydrogens it has, the better it is stabilised: 1° > 2° > 3°.
Steric hindrance: bulky alkyl groups crowd the nitrogen and hinder this hydrogen bonding; least for 1°, greatest for 3°, so on this count: 1° > 2° > 3°.
For ethyl-substituted amines, these factors together make the secondary amine the strongest base in water, followed by the tertiary and then the primary amine. Matching the given compounds:
(C) \( \ce{(Et)2NH} \): diethylamine (2°)
(D) \( \ce{(Et)3N} \): triethylamine (3°)
(A) \( \ce{EtNH2} \): ethylamine (1°)
(B) \( \ce{NH3} \): ammonia
NCERT (2026-27 edition):
Alkanamines versus Ammonia – …
