Interpretation of Hydrogen/Deuterium Isotope Effects on NMR Chemical Shifts of (FHF) − Ion Based on Calculations of Nuclear Magnetic Shielding Tensor Surface
ZEITSCHRIFT FUR PHYSIKALISCHE CHEMIE-INTERNATIONAL JOURNAL OF RESEARCH IN PHYSICAL CHEMISTRY & CHEMICAL PHYSICS(2003)
摘要
Using ab initio calculations of H-1, F-19 magnetic shielding tensors of hydrogen difluoride ion as the functions of three coordinates of symmetry, an attempt is made to estimate the contributions of different vibrational isotope effects to H/D NMR isotope shifts referred in the literature. It is shown that the contributions of the amplitudes of proton stretching and bending vibrations dominate whereas the contribution of the totally symmetric vibration can be neglected. Different signs of the H/D isotope effects on hydron and fluorine chemical shifts are caused by very strong angle dependence of the fluorine magnetic shielding. The agreement of the calculated and measured values is nearly quantitative. An unusually strong paramagnetic deshielding of hydrogen for the equilibrium geometry of the [FHF](-) ion is noted.
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关键词
hydrogen bonding,hydrogen difluoride,H/D isotope effect,NMR,shielding surfaces
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