Arrange the following in decreasing order of the basic character in aqueous phase
(A) Ethanamine
(B) Benzeneamine
(C) Phenylmethanamine
(D) N-methylaniline
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (A), (C), (D), (B)
Correct order of decreasing basic strength in aqueous phase:
(A) > (C) > (D) > (B)
i.e. Ethanamine > Phenylmethanamine > N-Methylaniline > Benzeneamine (Aniline)
Explanation (Kb or pKb order):
|
Compound |
Name |
Type |
Reason for basicity order |
Order |
|
(A) CH₃CH₂NH₂ |
Ethanamine |
Aliphatic 1° amine |
Pure +I effect, no resonance, full solvation of conjugate acid |
1 |
|
(C) C₆H₅CH₂NH₂ |
Phenylmethanamine |
Benzylamine |
+I effect dominates, phenyl not directly attached to N |
2 |
|
(D) C₆H₅NHCH₃ |
N-Methylaniline |
Aromatic 2° amine |
Lone pair partially delocalized into ring, but less than aniline (steric + hyperconjugation from methyl) |
3 |
|
(B) C₆H₅NH₂ |
Aniline (Benzeneamine) |
Aromatic 1° amine |
Lone pair strongly delocalized into benzene ring → least basic |
4 |