Conformational free energy difference (–ΔG° value) of the methyl group in methylcyclohexane: an accurate determination by the direct, low-temperature nuclear magnetic resonance method

Abstract

The low-temperature pulse Fourier transform ¹³C n.m.r. spectrum of methylcyclohexane, enriched with ¹³C in the methyl substituent, shows that the ratio of major conformation (methyl equatorial) to minor conformation (methyl axial) is 164 : 1 (0·6% methyl axial), corresponding to a conformational free energy difference at 172 K of 1·74 ± 0·06 kcal mol^–1(7·30 ± 0·25 kJ mol^–1).