Fluorine and Proton NMR Study of Gaseous Hydrogen Fluoride

Abstract

The 19F and 1H resonances for gaseous hydrogen fluoride were measured over the range from low pressure to saturated vapor. In each spectrum, only a single line is observed, which shows an unusually large and monotonic change in chemical shift with HF density. The monomer chemical shifts were determined by extrapolation, to zero total pressure, of data for mixtures with various foreign gases. The 19F chemical shifts, in parts per million relative to SiF4 gas at zero pressure, are HF (g, monomer): 46.85 ± 0.35 ppm, DF(g, monomer): 49.35 ± 0.35 ppm, HF (liq, cylinder): 25.53 ± 0.04 ppm. The 1H shifts relative to CH4 gas at zero pressure are HF(g, monomer): − 2.10 ± 0.20 ppm, HF (liq, cylinder): − 8.67 ± 0.02 ppm. These data are for 34°C, but the extrapolated monomer shifts appear to be practically independent of temperature. The absence of spin-spin splittings, and the observation of only a single averaged resonance in HF-DF mixtures, proves that there are rapid monomer-breaking exchange processes in the vapor. This is evidence for the presence of a ring polymer.