NMR-spektroskopische Untersuchungen an Chalkogenverbindungen, II [1]. 125Te-, 77Se-, 19F- und 13C-chemische Verschiebungen von CF3-substituierten Selen- und Tellurverbindungen [2] / NMR Spectroscopic Studies on Chalcogen Compounds, II [1]. 125Te-, 77Se-, 19F- and 13C Chemical Shifts of CF3 Substituted Selenium and Tellurium Compounds [2]

Abstract

⁷⁷Se chemical shifts of compounds CF₃SeX exhibit an extraordinary good linear correlation with Huggins‘ electronegativities of χx. A range of 1051 ppm is covered for χx values between 1.9 and 3.15. Effective electronegativities are derived from the δ(⁷⁷Se) values. For some compounds unexpected ⁷⁷Se chemical shifts are found. This indicates an uncommon electronic constitution at selenium. Electron excitation energies are reported for some of the compounds and their importance for the paramagnetic shielding term is discussed. The relative shieldings of the tellurium compounds are analogous to those of the corresponding selenium compounds. In contrast to ⁷⁷Se, the ¹⁹F shieldings of CF₃EX compounds (E = chalcogen) depend inversely on the electronegativity of E and X. The ¹³C chemical shifts do not correlate with the χx values. NMR data of some CF₃Se(IV) and CF₃Te(IV) compounds are also reported for comparison