Theoretical and infrared studies on the conformational isomerism of trans-2-bromo-alkoxycyclohexanes

The infrared spectra of trans-2-bromo-alkoxycyclohexanes (alcoxy = OMe, OEt, OiPr and OtBu) were obtained for the neat liquid, and the C–Br stretching mode was quantitatively analyzed to give insight about the conformational isomerism of these compounds. Frequency calculations supported the band assignments, and the relative band intensities suggest that the diaxial conformer is prevalent for the methoxy and tert-butoxy derivatives (51 and 56%, respectively), while the diequatorial form is preponderant for the ethoxy and isopropoxy derivatives (76 and 77%, respectively). Therefore, the size of the alkoxy group plays a determinant role in determining the conformational preferences of the title compounds.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights• The conformational equilibrium of 2-bromo-alkoxycyclohexanes was examined. • Theoretical calculations allowed the band assignments. • The C–Br stretching mode was analyzed. • Conformer populations are dependent on steric effects.