Why is carbon-nitrogen bond length in aromatic amines shorter than in aliphatic amines?

Explanation

Due to electron-donating resonance effect (+R-effect) of the `NH_2` group, the carbon-nitrogen bond in aromatic amines has some double bond character. In contrast, in aliphatic amines, the carbon-nitrogen bond has only single bond character. Therefore, carbon-nitrogen bond length in aromatic amines is shorter than in aliphatic amines.