Alkyl group effect on the conformational isomerism of trans-2-bromo-alkoxycyclohexanes analyzed by NMR spectroscopy and theoretical calculations

Abstract

Suitable 3JH,H coupling constants and theoretical calculations were used to define the conformational preferences of trans-2-bromoalkoxycyclohexanes (alkoxy = OMe, OEt, OiPr, and OtBu) for the isolated molecule and as a function of the medium. The diaxial conformer was preponderant, or at least similarly populated to the diequatorial form, for the tert-butoxy derivative only, while the diequatorial conformer was prevalent for the remaining alkoxy derivatives (except for the OMe derivative in CCl4 solution). The conformational behavior of these compounds was analyzed on the basis of classical steric effects and attractive electron delocalizations, by means of natural bond orbital analysis.