In chemistry, a nitrogen compound like ammonia in a trigonal pyramid geometry undergoes rapid nitrogen inversion whereby the molecule turns inside out.

This interconversion is a room temperature process because the energy barrier (24.2 kJ/mol) is relatively small. Contrast this to phosphine which does not show inversion at room temperature (energy barrier: 132 kJ/mol).

Even if all three substituents on the nitrogen in an amine are different, rapid inversion would prevent the nitrogen atom from becoming a permanent chiral center, since such inversion becomes effectively like a conformational change. However, if the nitrogen is a bridgehead atom in a bicyclo or a similar compound where it cannot invert around the lone electron pair, then the nitrogen atom could be a chiral center if all three substituents on it are effectively different. An example of such a compound is Tröger's base.

Reference

• Kölmel, C.; Ochsenfeld, C.; Ahlrichs, R. An ab initio investigation of structure and inversion barrier of triisopropylamine and related amines and phosphines. Theor. Chim. Acta. 1991, 82, 271-284. doi:10.1007/BF01113258

amines | chemistry