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 methyl 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 this and is diagnostic of an eclipsed conformation. The corresponding acyclic compound 2,4-dimethyl-3-methoxypentane is also concluded to have an eclipsed C–O bond.