ECLIPSED GROUND-STATE CONFORMATIONS FOR METHOXYCYCLOHEXANES WITH ADJACENT METHYL-GROUP SUBSTITUTION - AN NMR CRITERION AND MOLECULAR MECHANICS CALCULATIONS

Molecular mechanics calculations suggest that the conformation of the ring-to-oxygen bond in several methoxycyclohexanes with equatorial met hyl substituents in both the 2- and 6-positions is eclipsed. The three bond coupling constant of the methine proton with the methoxy carbon, which is large compared with that of methoxycyclohexane. confirms thi s and is diagnostic of an eclipsed conformation. The corresponding acy clic compound 2,4-dimethyl-3-methoxypentane is also concluded to have an eclipsed C-O bond.