Illustrated Glossary of Organic Chemistry

Nitrogen inversion: A process in which the lone pair of an sp³ nitrogen atom migrates from one face of the atom, travels through the nucleus (quantum tunneling), and reappears on the other side. This causes the nitrogen atom's substituents to move in a manner like an umbrella inverting in a strong wind. The two stereochemical configurations of the inverting nitrogen atom are in equilibrium. Nitrogen inversion does not occur if the inversion processes causes too much strain, or if the nitrogen atom lacks a lone pair (because of resonance or because it is an alkylammonium cation).


(S)-Ethyl methyl amine		(R)-Ethyl methyl amine

Nitrogen inversion causes the interconversion of the S and R enantiomers of ethyl methyl amine. K_eq = 1 and the rate of inversion is so fast that the enantiomers cannot be separated. Therefore so this molecule exists as a racemic mixture.

Quinuclidine (shown above) does not undergo nitrogen inversion because the nitrogen inversion transition state structure has too much ring strain. Test this with a model.

The tetramethylammonium cation (shown above) does not undergo nitrogen inversion because it has no nitrogen lone pair.