Match the List-I with List-II.
| List-I Compounds | List-II pKb (aqueous phase) |
| (A) N, N-Dimethylaniline | (I) 4.70 |
| (B) Phenylmethanamine | (II) 3.27 |
| (C) Benzenamine | (III) 8.92 |
| (D) N-Methylmethanamine | (IV) 9.38 |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A) - (III), (B) - (I), (C) - (IV), (D) - (II)
pKb = −log Kb, so a lower pKb means a stronger base. An amine is basic because the lone pair on nitrogen can take up a proton. Alkyl groups (+I) push electrons towards N and make it more basic. When N is attached directly to a benzene ring, its lone pair is delocalised into the ring by resonance, which makes it a much weaker base.
(A) N, N-Dimethylaniline — This matches (III) 8.92. N sits on the ring, so it is a weak base, but its two methyl groups (+I) make it a little stronger than aniline.
(B) Phenylmethanamine — This matches (I) 4.70. This is \( \ce{C6H5CH2NH2} \) (benzylamine). The CH2 group separates NH2 from the ring, so the lone pair is not delocalised and it behaves like an aliphatic amine.
(C) Benzenamine — This matches (IV) 9.38. Aniline’s lone pair is fully delocalised, so it is the weakest base with the highest pKb.
(D) N-Methylmethanamine — This matches (II) 3.27. \( \ce{(CH3)2NH} \) is a 2° aliphatic amine with two +I methyl groups, so it is the strongest base with the lowest pKb.
Shortcut: The pair (B)–(I) appears only in Option (3).
NCERT (2026-27 edition):
Chemical Reactions
| Name of amine | pKb |
|---|---|
| Methanamine | 3.38 |
| N-Methylmethanamine | 3.27 |
| N,N-Dimethylmethanamine | 4.22 |
| Ethanamine | 3.29 |
| N-Ethylethanamine | 3.00 |
| N,N-Diethylethanamine | 3.25 |
| Benzenamine | 9.38 |
| Phenylmethanamine | 4.70 |
| N-Methylaniline | 9.30 |
| N,N-Dimethylaniline | 8.92 |