An 2H(D) isotope shift in the 1H NMR spectra of water in gaseous environment of fluoromethanes

Measurements of 1H chemical shifts in H216O and HD16O molecules in gaseous mixtures with excess of fluoromethanes CHnF4 − n with n ⩽ 4 have been obtained. Over the range of accessible pressures of the gaseous buffers used at room temperature the proton chemical shift vs. density of the medium relation are linear for either isotopomer and can be subjected to linear regression analysis. This analysis allowed to find the proton shielding constants in isolated water molecules. The isotope effect associated with this shieldings 2Δ1H (2/1H) was evaluated to be 0.0386 ppm and the value was compared with the available literature data. The new result for the isotope effect shows a better fit to the results obtained by the ab initio calculations, than the experimental data thus far known for liquid phase. Obviously, for the strongly polar water molecules the interactions in liquids are very strong and significantly affect the 1H shielding parameters. Thus measurements in gaseous solutions proved expedient, with extrapolation of the results to a zero pressure. The effect of molecular interactions in the CHnF4 − n/H2O/HDO systems on the shielding of protons of water in the gaseous complexes formed were discussed. The spin-spin coupling 2J(1H, 2H) was measured experimentally (−1.06 Hz) in the partly deuterated water in gas phase for the first time. The coupling constant 2J(1H, 1H) found on this basis is −6.89 Hz.