Photoelectron spectroscopic investigations indicate that (i) monocyclic diaziridines prefer a trans‐conformation of the nitrogen‐lone pairs, and (ii) the interaction between these is comparable to that exhibited by open‐chain analogues, i.e. alkyl‐substituted hydrazines. The chemical experience concerning the particular case of NHNH→NN oxidation of diaziridines can therefore not be accounted for by a prevailing unfavorable ‘lone pair’ interaction. Thermochemical as well as entropy arguments may serve as an explanation. A rather unsatisfactory agreement between predictions from various theoretical procedures and experimental results for the ionization potentials of ‘lone pair’ MO electrons is noted.