 Pyramidal inversion

Interconversion of the two spatial orientations of a three-coordinate pyramidal centre through a flatter geometry. Quaternary ammonium nitrogen has no lone pair and cannot follow the ordinary three-coordinate amine pathway.

Pyramidal inversion is a phenomenon that occurs in certain molecules where the configuration of a chiral center can interconvert between two different arrangements. Specifically, this term is often used in the context of molecules that adopt a pyramidal geometry at a nitrogen or phosphorus atom. In a pyramidal structure, the central atom is bonded to three other atoms or groups in a manner that gives it a trigonal pyramidal shape, resembling a pyramid.