The rotation-dominated ring inversion/nitrogen inversion/rotation process in N-acyloxy-2,2,6,6-tetramethylpiperidines. A dynamic NMR study

Abstract

The temperature dependence of the NMR spectra of a series of N-acyloxy-2,2,6,6-tetramethylpiperidines is reported and discussed in terms of a conformational process which involves ring inversion, nitrogen inversion and rotation about the nitrogen–oxygen bond. Nitrogen inversion contributes ca. 11 kcal mol^–1 to the observed barriers, so in the compounds with higher barriers, steric interaction of the acyl and methyl groups during rotation determines the barrier height.