Intermolecular effects on spin–spin coupling and magnetic shielding constants in gaseous difluoromethane

Abstract

Difluoromethane (CH 2F 2) has been studied using 1H, 13C and 19F nuclear magnetic resonance (NMR) spectra in the gas phase at 300 K. For the first time all indirect spin–spin couplings in CH 2F 2 were measured as functions of density. 1H, 13C and 19F magnetic shielding constants were also monitored at various densities. After extrapolation to the zero-density limit the relevant values of an isolated CH 2F 2 molecule ( J 0 and σ 0) were obtained. It was shown that the influence of intermolecular interactions on the NMR spectral parameters of CH 2F 2 is rather significant. Strong linear density-dependence was found for the 1 J CF and 1 J CH spin–spin coupling constants while the 2 J FH coupling constant was almost independent of density in the gas phase. All the shielding constants of CH 2F 2 ( σ H, σ C and σ F) had linear density-dependence and they were diminished with the increase of gas density. Isotope effects in 19F shielding of CH 2F 2 have been determined when the 13CH 2F 2 and CHDF 2 isotopomers were observed at the natural abundance of the heavier nuclei.