Long range 13C shift effects (δ and ϵ) in methylcyclohexanes

¹³C n.m.r. spectra of a number of methyl substituted cyclohexanes, some of them conformationally homogeneous, have been recorded in CDCl₃ and used to determine shift effects engendered by the introduction of methyl groups on carbon atoms remote from the site of substitution. Sizeable changes in shifts are found, including a substantial effect of an equatorial methyl group on an axial methyl group δ to it (+0.6₇ ppm, ‘δ_ea’). The effects reported are of consequence in investigations of conformational problems by ¹³C n.m.r. techniques.