Decreasing order of basicity for the following compounds:
(A) Ethylamine
(B) Diethylamine
(C) Ammonia
(D) Benzenamine
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (B), (A), (C), (D)
The basic strength of an amine depends on how easily the lone pair on nitrogen is available to take a proton. Three factors decide it:
+I effect of alkyl groups: ethyl groups push electron density onto nitrogen, so alkylamines are stronger bases than ammonia; on this factor alone, more ethyl groups means a stronger base.
Solvation of the cation in water: the ammonium ion is stabilised by hydrogen bonding with water through its N–H bonds; more N–H bonds give better solvation.
Resonance in arylamines: in aniline the lone pair is spread into the benzene ring, so it is much less available, and aniline is weaker than ammonia.
For the ethylamines in water, the +I effect and solvation together put the secondary amine first, then the primary amine:
\( \displaystyle \text{secondary amine} \gt \text{primary amine} \gt \text{ammonia} \gt \text{arylamine} \)
\( \displaystyle \ce{(C2H5)2NH} \gt \ce{C2H5NH2} \gt \ce{NH3} \gt \ce{C6H5NH2} \)
(B) \( \ce{(C2H5)2NH} \): diethylamine (secondary amine)
(A) \( \ce{C2H5NH2} \): ethylamine (primary amine)
(C) \( \ce{NH3} \): ammonia
(D) \( \ce{C6H5NH2} \): benzenamine, aniline (arylamine)
Shortcut: Aniline is the weakest of the four, so the order must end with (D): Options (1), (2) and (3). Diethylamine is stronger than ethylamine, so (B) comes before (A), which leaves Option (3).
NCERT (2026-27 edition):
Basic Character of Amines – …
