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METHYLTRITHIOPHOSPHONIC ACID AND RELATED COMPOUNDS - SYNTHESIS, SOLUTION, AND SOLID-STATE NMR SPECTROSCOPY AS WELL AS SHIELDING TENSOR CALCULATIONS

1996; Taylor & Francis; Volume: 116; Issue: 1 Linguagem: Inglês

10.1080/10426509608040476

1563-5325

J. Hahn, U. Drexler, S. Oimann, G. Großmann, Gisela Ohms, Kerstin Krüger,

Organophosphorus compounds synthesis

Abstract Methyltrithiophosphonic acid (1) has been prepared in a pure state. The thermal decomposition of 1 into 2,4-dimethyl-2,4-dithio-1,3,2,4-dithiadiphosphetane (3) proceeds via dimethylpentathiodiphosphonic acid (2), which has been characterized by its 1H and 31P high resolution NMR parameters and by a derivatization reaction with norbornadiene. Solid-state 31P CP MAS spectra of 1, 3, and the related compounds, 3,5-dimethyl-3,5-dithio-1,2,4,3,5-trithiadiphospholane (4), and 3,6-dimethyl-3,6-dithio-1,2,4,5,3,6-tetrathiadiphosphorinane (5), have been measured. The experimentally determined phosphorus anisotropic shielding tensors are compared with results of IGLO calculations. From a comparison of the experimental values with those calculated for different geometry optimized conformations of 1, 4, and 5 structural assignments became possible: In the solid state 1 most probably shows a trans orientation of the H-S-P─S unit, 4 probably realizes a half-chair and 5 a chair conformation, both with bisaxial orientation of the methyl groups. Using the orientation of the shielding tensor in the molecular framework obtained from IGLO calculations and the experimentally determined [sgrave]ii values, the calculated shielding ovaloids have been plotted in order to visualize the variation of the shielding value in dependence on the molecule orientation relative to the magnetic field direction. The shielding or deshielding contributions of localized molecular orbitals (LMO) available from IGLO calculations have also been inspected Principal axis 3, corresponding to the most shielding value [sgrave]33, nearly coincides with the P─S double bond for all molecules. In spite of large deshielding contributions from P-C and P-S single bonds the high shielding along this axis results from the very low P─S LMO contribution.