Solvent Effects on H–F Couplings: Dipole Orientation Requirements for Solvent Dependence of Coupling Constants

Abstract

Solvent‐dependent variations of ²J_HF, cis ³J_HF, and trans ³J_HF have been observed in trifluoroethylene and vinyl fluoride. These data, in conjunction with previous observations, indicate that orientation of the solute dipole strongly affects the solvent dependence of geminal coupling constants. The electric field of the solvent appears to be the primary causative factor, but strong molecular associations (e.g., H bonding) may either enhance or decrease the observed effect. The limited results available suggest that the absolute sign of ²J_HF may be obtained by observing the change of ²J_HF as a function of solvent.