Nitrogen inversion and N-O bond rotation in some hydroxylamine and isoxazolidine derivatives

A series of trisubstituted hydroxylamine derivatives, both cyclic and acyclic, has been prepared. The energy barriers in these hydroxylamines are found to be dominated either by nitrogen inversion or N-O bond rotation depending on the nature of the substituents attached to the nitrogen. In several series of compounds, having XC₆H₄CH₂ substituents attached to nitrogen, Hammett free energy correlations are obtained with positive ρ values, indicating increased electron density at the transition state for the inversion process. Isoxazolidines with C(5) ethoxy substituents demonstrate a strong anomeric effect.