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Theoretical study on the stereochemistry of bis(methylthio)methane, a model of dithioacetal segment in thiosaccharides

I. Tvaroška

Institute of Chemistry, Centre for Chemical Research, Slovak Academy of Sciences, CS-842 38 Bratislava


Abstract:  The stereochemistry of bis(methylthio)methane, a model of dithioacetal segment in thiosaccharides, was studied by the semiempirical quantum chemical methods. PCILO method was applied for calculation of the conformational map of rotation around the central С—S bonds. The geometry of stable conformations sc,sc, sc,ар, and ар,ар was optimized by MNDO method. The ratio of individual conformers in the isolated molecule, calculated on the basis of MNDO energies, was 78:21:1. Influence of a solvent was calculated by the procedure, which involved contributions of electrostatic and dispersion interac­tions and a cavity term. Contribution of electrostatic interactions was shown to be the most conformationally dependent. Populations of conformers in dilute solutions depend on a solvent character and the proportion of conformers with the antiperiplanar positions of the methyl groups increases with the increasing polarity of solvent. In methanol, for example, the proportion of conformers is already 57:40:3, and in water 31:59:10; while sc,ар conformer was shown to be the most stable. Comparison with the oxygen analogues revealed that both anomeric and exoanomeric effects in dithioacetal segment are lower than in acetal one.

Full paper in Portable Document Format: 382a189.pdf


Chemical Papers 38 (2) 189–197 (1984)

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