Probing Nuclear Dipole Moments and Magnetic Shielding Constants through 3-Helium NMR Spectroscopy

Abstract

Multinuclear NMR studies of the gaseous mixtures that involve volatile compounds and 3He atoms are featured in this review. The precise analyses of 3He and other nuclei resonance frequencies show linear dependencies on gas density. Extrapolation of the gas phase results to the zero-pressure limit gives the ν0(3He) and ν0(nX) resonance frequencies of nuclei in a single 3-helium atom and nuclei in molecules at a given temperature. The NMR frequency comparison method provides an approach for determining different nuclear magnetic moments. The application of quantum chemical shielding calculations, which include a more complete and careful theoretical treatment, allows the shielding of isolated molecules to be achieved with great accuracy and precision. They are used for the evaluation of nuclear moments, without shielding impacts on the bare nuclei, for: 10/11B, 13C, 14N, 17O, 19F, 21Ne, 29Si, 31P, 33S, 35/37Cl, 33S, 83Kr, 129/131Xe, and 183W. On the other hand, new results of nuclear moments were used for the reevaluation of absolute nuclear magnetic shielding in the molecules under study. Additionally, 3He gas in water solutions of lithium and sodium salts was used for measuring 6/7Li and 23Na magnetic moments and reevaluating the shielding parameters of Li+ and Na+ water-solvated cations. In this paper, guest 3He atoms that play a role in probing the electron density in many host macromolecules are also presented.

Keywords

• nuclear magnetic dipole moment
• nuclear magnetic shielding
• gas-phase NMR