Question

Give a plausible explanation for the following:

Why are aliphatic amines stronger bases than aromatic amines?

Answer 1

Due to the −R effect of the benzene ring, the electrons on the N- atom are less available in the case of aromatic amines. Therefore, the electrons on the N-atom in aromatic amines cannot be donated easily. This explains why aliphatic amines are stronger bases than aromatic amines.

Answer 2

Aromatic amines are far less basic than ammonia and aliphatic amines because of the following reasons:

1. Due to resonance in aniline and other aromatic amines, the lone pair of electrons on the nitrogen atom gets delocalised over the benzene ring and thus it is less easily available for protonation. Therefore, aromatic amines are weaker bases than ammonia and aliphatic amines.
2. Aromatic amines are more stable than corresponding protonated ions; Hence, they have very little tendency to combine with a proton to form a corresponding protonated ion, and thus they are less basic.