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

<jats:title>Abstract</jats:title><jats:p> Nineteen values for <jats:sup>34</jats:sup>S-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 <jats:sup>1</jats:sup>Δ<jats:sup>19</jats:sup>F(<jats:sup>34/32</jats:sup>S) 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, <jats:sup>34</jats:sup>S-induced isotope shifts on fluorine-19 over two bonds, <jats:sup>2</jats:sup>Δ<jats:sup>19</jats:sup>F(<jats:sup>34/32</jats:sup>S), have been observed for the first time, and the <jats:sup>33</jats:sup>S-induced isotope effect in SF<jats:sub>6</jats:sub> has been measured. </jats:p>