Quantitive dependence of N-methyl inversion barriers in six-membered rings on electronic and steric effects. Direct observation of the conformational equilibria in tetrahydro-1,3-oxazines and hexahydropyrimidines

Abstract

Low-temperature ¹H n.m.r. spectra of N-methyl and N,C-polymethyl derivatives of tetrahydro-1,3-oxazine and hexahydropyrimidine allow calculation of conformational equilibria and the rationalisation of steric and electronic effects on N-methyl inversion barriers.