Solvent Effects on Hsngbnd;F Couplings: Dipole Orientation Requirements for Solvent Dependence of Coupling Constants

摘要

Solventhyphen;dependent variations of2JHF,cis3JHF, andtrans3JHFhave 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 of2JHFmay be obtained by observing the change of2JHFas a function of solvent.