13C, 2H coupling constants and 2H-induced 13C NMR isotope chemical shifts in deuteriated cyclohexanes: application for measurements of conformational equilibrium isotope effects

Abstract

¹³ C, ²H coupling constants and ²H-induced ¹³C isotope shifts have been measured in [²H₁]-cyclohexane 1 and [1,1-²H₂]cyclohexane 2. We have observed differences in ¹³C, ²H coupling constants in 1 and 2 and also between the ¹³C isotope shifts in 1 and 2 for each deuterium substitution. The observed differences in coupling constants for C¹, C² and C³ are sums of intrinsic and thermodynamic effects and the intrinsic contribution predominates for C¹ while the thermodynamic contribution predominates for C³. The differences in the ¹³C isotope shifts are almost completely due to the non-additivity effects. Thus only the vicinal isotope effects for ¹³C, ²H or ¹³C, H coupling constants can be expected to be used for the estimates of shifts of conformational equilibria in deuteriated cycloalkanes.