NMR-spektroskopische Untersuchungen an Chalkogenverbindungen, VI [1]. 34S-Isotopeneffekte auf 19F-NMR-Frequenzen und ihre Abhängigkeit von Bindungslängen / NMR Spectroscopic Studies on Chalcogen Compounds, VI [1] l4.34S Isotope Effects on 19F-NMR Frequencies and their Dependence on Bond Lengths

Abstract

Abstract Nineteen values for 34S-induced isotope shifts on the NMR frequency of directly bonded fluorine of fourteen S(II), S(IV), and S(VI) compounds are reported. The dependence of these 1Δ19F(34/32S) values on the S-F bond length is demonstrated. Three reasons for this correlation are discussed. (1) A nonlinear dependence of nuclear shielding on bond distance. (2) Decreasing energy difference of two isotopomers with increasing bond distance. (3) Decreasing anharmonicity of the potential curve with increasing bond length. Some previously unknown S-F bond distances have been estimated by this correlation. The isotope shifts decrease with increasing temperature. This is attributed to vibrationally excited states in conjunction with a nonlinear dependence of nuclear shielding on bond distance. Furthermore, 34S-induced isotope shifts on fluorine-19 over two bonds, 2Δ19F(34/32S), have been observed for the first time, and the 33S-induced isotope effect in SF6 has been measured.