Arrange the following in increasing order of their basic strength in aqueous phase:
(A) $CH_3NH_2$
(B) $C_6H_5CH_2NH_2$
(C) $C_6H_5NH_2$
(D) $(CH_3)_3N$
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (C), (B), (D), (A)
(C) Aniline ($C_6H_5NH_2$) – Least basic: The lone pair on nitrogen is delocalised into the benzene ring due to resonance, so it is less available to accept a proton.
(B) Benzylamine ($C_6H_5CH_2NH_2$: The $-CH_2-$ group breaks resonance with the ring, so the lone pair is more available than in aniline.
(D) Trimethylamine ($(CH_3)_3N$): Alkyl groups show $+I$ effect and increase electron density on nitrogen, but in aqueous solution steric hindrance and poor solvation reduce its basic strength compared to methylamine.
(A) Methylamine ($CH_3NH_2$) – Most basic: Strong $+I$ effect and good solvation in water make it the strongest base among these.