Question

Which amines form stronger bases:aliphatic or aromatic amines?

Answer 1

Aliphatic amines are clearly the stronger bases.

Explanation:

The lone pair on an aromatic amine is conceived to be delocalized to some extent about the aromatic ring. For the aliphatic amine, the lone pair is confined to the nitrogen atom. Given this, the nitrogen lone pair of the aniline derivative is less available for donation to `H^+`. Because we are physical scientists, however, we should look at actual values of basicity. The `pK_a` values of the anilinium cation, `C_6H_5NH_3^+` is 4.6 whereas for methyl ammonium cation, `H_3C-NH_3^+`, it is 10.6. How is this consistent with the argument about their respective basicities of the free bases?