How does the basicity of aliphatic amines compare with that of ammonia?

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amine Examples of different types of amines.

Aliphatic amines are generally stronger bases than ammonia.12

The basicity of these compounds is measured by their $p K_{b}$ value, where a larger $p K_{b}$ indicates a weaker base. For comparison, ammonia has a $p K_{b}$ of 4.75. In contrast, most aliphatic amines exhibit lower $p K_{b}$ values, reflecting their increased basic strength.1

This difference in basicity is largely attributed to the presence of alkyl groups, which act as electron-repelling substituents. These groups increase the electron density on the nitrogen atom, thereby enhancing the molecule's ability to accept a proton and act as a base. Conversely, electron-attracting substituents would have the opposite effect, making a base weaker.2