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. Precise analyses of the 3He and other nuclei resonance frequencies show linear dependences on the gas density. Extrapolation of the gas phase results to the zero-pressure limit gives 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. 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 evaluation of nuclear moments without shielding impact on bare nuclei: 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 reevaluation of absolute nuclear magnetic shielding in molecules under study. Additionally, 3He gas in water solutions of lithium and sodium salts was used for measurements of 6/7Li and 23Na magnetic moments and reevaluation of 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 presented as well.