2 -Substituted 1,3-dithianes conformational analysis

Ab initio calculations at the MP2 level of theory of a collection of substituted 1,3-dioxanes, 1,3-oxathianes, and 1,3-dithianes have been employed to study both the position of the conformational equilibria and the validity of the Perlin effect <2005T7349>. The 7h,c coupling constant proved to be a valuable tool in conformational analysis both twist conformers, in addition to the chair and alternative chair forms, could be readily identified simply by comparing experimental Vh,c coupling constants to the corresponding calculated values in the particular forms. In addition, the Perlin and reversed-Perlin effects of the C2-H fragments, c in 1,3-dioxanes,... 

In contrast to a thoroughly performed conformational analysis of 1,4-dioxanes and 1,4-oxa-thianes, the data on the conformational behavior of 1,4-dithianes are quite limited. According to NMR ( H, C) spectroscopy and molecular mechanics calculations, 2-alkyl-substituted 1,4-dithianes exist preferentially in the conformation with equatorially oriented substituents. For 1,4-dithianes with substituents of tbe CHjX type (X = aeetoxy, halogen), the predominance of axial conformers is observed originating from an intramolecular electrostatic attraction <91T9455). 

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