JEE Main 2025 · 7 April · evening · Single correct · +4 / −1
The descending order of basicity of the following amines is :
(D) CH₃NH₂
(E) (CH₃)₂NH
Choose the correct answer from the options given below :
- (a) E > A > D > C > B
- (b) E > D > A > B > C
- (c) E > D > B > A > C
- (d) B > E > D > A > C
Answer and solution
Answer (c) E > D > B > A > C
Solution
Chemistry ma’am · 3 steps
Aliphatic amines first, then rank the anilines by whether the para group pushes or pulls electrons.
- Aliphatic beat aromatic. In D and E the nitrogen lone pair stays on nitrogen, and the methyl groups push electron density onto it. In A, B and C the lone pair is delocalised into the benzene ring, so it is much less available for a proton.
- Among aliphatic amines. (CH₃)₂NH has two electron-donating methyl groups and its cation is still well solvated. In water this makes it a stronger base than CH₃NH₂, so E > D.
Amine Para group Effect on the lone pair pK_b (approx.) E, (CH₃)₂NH none (aliphatic) two +I methyl groups 3.3 D, CH₃NH₂ none (aliphatic) one +I methyl group 3.4 B, p-anisidine -OCH₃, +R donor ring gets electron-rich, lone pair more available 8.7 A, aniline -H lone pair delocalised into ring 9.4 C, p-nitroaniline -NO₂, -R and -I withdrawer lone pair pulled strongly into the nitro group 13.0 - So. Higher pK_b means a weaker base, so the descending order is E > D > B > A > C, which is option (c).
The idea to keep. For substituted anilines, compare with aniline: a para donor like -OCH₃ raises basicity, a para withdrawer like -NO₂ lowers it sharply. Simple aliphatic amines beat them all.
Answer from the NTA final answer key. Solution by PrepWiser.