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

Abstract

Difluoromethane (CH2F2) 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 CH2F2 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 CH2F2 molecule (J0 and σ0) were obtained. It was shown that the influence of intermolecular interactions on the NMR spectral parameters of CH2F2 is rather significant. Strong linear density-dependence was found for the 1JCF and 1JCH spin–spin coupling constants while the 2JFH coupling constant was almost independent of density in the gas phase. All the shielding constants of CH2F2 (σH, σC and σF) had linear density-dependence and they were diminished with the increase of gas density. Isotope effects in 19F shielding of CH2F2 have been determined when the 13CH2F2 and CHDF2 isotopomers were observed at the natural abundance of the heavier nuclei.