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

ABSTRACT 19 F NMR spectra were recorded in gaseous CFCl 3 /Xe mixtures on the NMR spectrometer, operated with a standard 2 H(D) lock system. These results and shielding values obtained from the best relativistic quantum chemical calculations for single isolated CFCl 3 were used to establish the 19 F nuclear magnetic moment: μ ( 19 F) = 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 Δ σ gl = −5.28(1) ppm. Next, the 1 H, 19 F, and 3 He NMR spectra were measured in CH 3 F/ 3 He and CF 4 / 3 He gaseous mixtures as density functions. Extrapolating linear relationships to the zero‐pressure limit yields frequency parameters for isolated CH 3 F, CF 4 , and helium atoms. These results have verified shielding constants for both fluorinated simple molecules. New exact results for the absolute 19 F shielding of 16 chemical compounds measured in the gas phase were reported. Based on the new 19 F shielding constant of the reference liquid CFCl 3 , a large set of previously measured shielding constants for fluorine compounds in the gas phase was obtained.