Conformational preferences of some substituted methyl groups in cyclohexanes as studied by carbon‐13 nuclear magnetic resonance

Low temperature 13 C NMR spectra of 80:20 mixtures of cis and trans ‐4CH 3 CH 3 C 6 H 10 CH 2 X, where C 6 H 10 ‐is 1, 4‐disubtituted cyclohexyl and X=Br, CN, OH, OCH 3 , Si(CH 3 ) 3 , Sn(CH 3 ) 3 , Pb(CH 3 ) 3 and HgOCOCH 3 have been recorded. The signals of the trans (e, e) components were assigned from the ambient temperature spectra of C 6 H 11 CH 2 X and the established substituent effects of an equatorial methyl group in cyclohexane. Conformational equilibria of the cis (e, a⇄a, e) components were then computed from the intensities of the (remaining) signals (∼180 K) of the two conformational isomers. From these equilibria A values of CH 2 X were calculated, assuming additivity of conformational energies of CH 3 and CH 2 X (the counter‐poise approach). In general, these values are very similar to the value of the CH 3 , although some trends do emerge. This study provides α, β, γ, and δ effects for a wide range of axial and equatorial CH 2 X groups.