Conformational Preferences of some Substituted Methyl Groups in Cyclohexanes as Studied by Carbon-13 Nuclear Magnetic Resonance

Article abstract of DOI:10.1002/mrc.1270150304

Low temperature 13C NMR spectra of 80 : 20 mixtures of cis and trans-4-CH3-C6H10CH2X, where -C6H10- is 1,4-disubstituted cyclohexyl and X=Br, CN, OH, OCH3, Si(CH3)3, Sn(CH3)3, Pb(CH3)3 and HgOCOCH3 have been recorded.The signals of the trans (e, e) components were assigned from the ambient temperature spectra of C6H11CH2X 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 (ca. 180 K) of the two conformational isomers.From these equilibria A values of CH2X were calculated, assuming additivity of conformational energies of CH3 and CH2X (the counter-poise approach).In general, these values are very similar to the value of CH3, although some trends do emerge.This study provides α, β, γ and δ effects for a wide range of axial and equatorial -CH2X groups.