Gas-Phase Studies of ¹⁹F NMR Magnetic Shielding of Simple Isolated Molecules

¹⁹F NMR spectra were recorded in gaseous CFCl₃/Xe mixtures on the NMR spectrometer, operated with a standard ²H(D) lock system. These results and shielding values obtained from the best relativistic quantum chemical calculations for single isolated CFCl₃ were used to establish the ¹⁹F nuclear magnetic moment: μ(¹⁹F) = 2.6283258(27) μ_N and a new absolute shielding scale based on liquid trichlorofluoromethane. The fluorine gas-to-liquid shift for trichlorofluoromethane was measured as Δσ_gl = -5.28(1) ppm. Next, the ¹H, ¹⁹F, and ³He NMR spectra were measured in CH₃F/³He and CF₄/³He gaseous mixtures as density functions. Extrapolating linear relationships to the zero-pressure limit yields frequency parameters for isolated CH₃F, CF₄, and helium atoms. These results have verified shielding constants for both fluorinated simple molecules. New exact results for the absolute ¹⁹F shielding of 16 chemical compounds measured in the gas phase were reported. Based on the new ¹⁹F shielding constant of the reference liquid CFCl₃, a large set of previously measured shielding constants for fluorine compounds in the gas phase was obtained.