Nitrogen inversion

Nitrogen inversion in ammonia

Inversion of an amine. The pair of dots represents the lone electron pair on the nitrogen atom.

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) ^[1]. 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.

In one study the inversion in an aziridine was slowed down by a factor of 50 by placing the nitrogen atom in the vicinity of a phenolic alcohol group compared to the oxidized hydroquinone ^[2] :

The system interconverts by oxidation by oxygen and reduction by sodium dithionite.

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