Answer
Basicity of Amines
Aliphatic amines are stronger bases than aromatic amines because the lone pair on the nitrogen atom in aliphatic amines is localized and readily available to accept a proton. In aromatic amines (like aniline), the lone pair on nitrogen is delocalized due to conjugation with the benzene ring, making it less available for protonation.
Among aliphatic amines, basicity increases with:
- Greater +I effect (inductive effect)
- Hyperconjugation
This leads to the following order:
Secondary amines (–N(Et)2) > Primary amines (–NHEt)
In anilines, the conjugation of the nitrogen lone pair with the benzene ring withdraws electron density from the nitrogen. However, a methyl group (–CH₃) can donate electron density through the +I effect and partially offset this, slightly increasing basicity.
Therefore, the correct order of basicity is:
N-ethylethanamine > ethanamine > N-methylaniline > benzenamine