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

Abstract 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, ‘δea’). The effects reported are of consequence in investigations of conformational problems by 13C n.m.r. techniques.