Pyramidal inversion

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Nitrogen inversion: The amine C3 axis is horizontal; the pair of dots represent the lone pair (on that axis). Note that the two amine molecules are symmetric across a mirror plane. If the three R groups attached are all unique, then the amine is chiral; isolability depends on the free energy required to invert the molecule.

In chemistry, pyramidal inversion (also umbrella inversion) is a fluxional process in compounds with a pyramidal molecule, such as ammonia (NH3) "turns inside out". It is a rapid oscillation of the atom and substituents, the molecule or ion passing through a planar transition state. For a compound that would otherwise be chiral due to a stereocenter, pyramidal inversion allows its enantiomers to racemize. The general phenomenon of pyramidal inversion applies to many types of molecules, including carbanions, amines, phosphines, arsines, stibines, and sulfoxides.

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