Aziridines N-non substituées: XI—Inversion de l'azote dans des composes C-substitués symetriquement ou non de part et d'autre du cycle

The occurrence of nitrogen inversion in 2- and/or 3-substituted aziridines has been proved by ¹H n.m.r. Only one invertomer was found when the difference in the bulkiness of the substituents on opposite sides of the ring is very great. From the different chemical shifts and the coupling constants of HC? NH one can show that the preferential invertomer, or the only invertomer, is always the one that has the N? H proton on the least hindered ring side. For the symmetrically substituted aziridines the energy barrier measurements have shown a decrease in the energy of the inversion as the steric hindrance of the molecule increases. A new stabilization factor, due to the preferential conformations of the aromatic ring, was found for the invertomers of phenyl substituted aziridines.