Arrange the following amines in increasing order of basicity in aqueous solution
(A) $(CH_3)_2NH$
(B) $CH_3NH_2$
(C) $(CH_3)_3N$
(D) $NH_3$
Choose the correct answer from the options given below.
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (D), (C), (B), (A)
Basicity of amines in aqueous solution depends on:
- +I effect of alkyl groups
- Hydration (solvation) of the protonated amine — this stabilizes the conjugate acid.
General order in aqueous medium:
$\text{Secondary amine} > \text{Primary amine} > \text{Tertiary amine} > \text{Ammonia}$
Reason:
- Secondary amines are most basic due to strong +I effect + good hydration.
- Tertiary amines are less hydrated, so they become less basic than primary in water.
Given amines:
(A) (CH₃)₂NH → secondary amine → most basic
(B) CH₃NH₂ → primary amine
(C) (CH₃)₃N → tertiary amine
(D) NH₃ → least basic
Increasing order of basicity (least → most):
$\text{NH₃} < \text{(CH₃)₃N} < \text{CH₃NH₂} < \text{(CH₃)₂NH}$
✔ Correct order: (D), (C), (B), (A)