A direct determination of the position of equilibrium in trans-1,2-dimethylcyclohexane

Abstract

The ¹³C n.m.r. spectrum of trans-[1-methyl-¹³C]-1,2-dimethylcyclohexane at 169 K reveals a single due to the methyl carbons of the trans-diaxil conformation (equilibrium constant ca. 3 655; –ΔG°_aa→eeca. 2.75 kcal mol^–1), whilst studies of the broadening of the natural abundnce ¹³C signals in the range 195–240 K yield a more accurate value for –ΔG°_aa→ee of 2.58 ± 0.05 kcal mol^–1, in good agreement with calculations by Allinger.