Ethyl-group rotational barriers in hindered trialkylamines. A dynamic NMR and molecular mechanics investigation

Abstract

The stereodynamics of N-ethyl-N-tert-butylneopentylamine 2 and three similar compounds 3–5, are reported and discussed. Dynamic NMR spectroscopy yields experimental barriers to nitrogen inversion–rotation, N–tert-alkyl bond rotation and N–ethyl bond rotation for 2 of 8.1, 7.3 and 6.0 kcal mol^–1, respectively, and shows that two different conformations about the latter bond are populated in the ratio 9 : 1. Molecular mechanics calculations fit well with these observations indicating which these conformations are and yielding a calculated ethyl group rotation barrier in good accord with experiment. Comparable results are obtained for the other three compounds.