The energy barrier for inversion of a tetrahedral (sp3) nitrogen atom is influenced by various structural features.

In the case of the chloroaziridine 1, the pyramidal N atom bears an electronegative chlorine and is part of a strained three-membered ring. This combination gives rise to significant configurational stability at room temperature.

Stereochemical inversion of pyramidal nitrogen in 1-chloro-2,2-diphenylaziridine
X-Ray structure of (<em>R</em>)-1-chloro-2,2-diphenylaziridine
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Absolute configuration of a chiral N-chloroaziridine with molecular asymmetry due solely to a trivalent nitrogen atom. X-Ray structure of (R)-(−)-1-chloro-2,2-diphenylaziridine; S. Brückner, A. Forni, I. Moretti and G. Torre, J. Chem. Soc., Chem. Commun., 1982, 1218–1219 (DOI: https://doi.org/10.1039/C39820001218).

Relationships between solid-state structures of enantiomers and the corresponding racemic compounds in small ring derivatives. Comparison of crystal structures and solid-state properties of (R)-(–)- and racemic 1-chloro-2,2-diphenylaziridine. Solvent effect on the racemization of (R)-(–)-1-chloro-2,2-diphenylaziridine; A. Forni, I. Moretti, G. Torre, S. Brückner, L. Malpezzi and G. Di Silvestro, J. Chem. Soc., Perkin Trans. 2, 1984, 791–797 (DOI: https://doi.org/10.1039/P29840000791).