BRAINCAKERelative Base Strength of Amines
Ammonia, primary aliphatic amines and primary aromatic amines are all bases, but they differ in strength. Base strength depends on how available the lone pair on the nitrogen is to accept a proton. The more electron density on the nitrogen, the more strongly the lone pair attracts H+ and the stronger the base.
Primary aliphatic amines are stronger bases than ammonia. Alkyl groups have a positive inductive effect: they release electrons towards the nitrogen. This increases the electron density on the nitrogen, so its lone pair is more available. For example, ethylamine is a stronger base than ammonia.
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