X-Ray crystal structure conformational studies on r-4,c-6-dimethyl-1,3-dithian and its oxides, r-4,c-6-dimethyi-1,3-dithian t-1 -oxide, and r-4,c-6-dimethyl-1,3-dithian t-1,t-3-dioxide

Abstract

The crystal structures of the title compounds [the 1,3-dithian (I), and its oxides (II) and (III)] have been determined from X-ray diffractometer data. Monoclinic crystals of (I) and (II) are isomorphous, space group C2/c, with for (I) : a= 20.08(1), b= 5.71(1). c= 15.69(1)Å. β= 118.4(1)°; and for (II) : a= 20.33(1), b= 5.68(1), c= 16.11(1)Å. β= 119.0(1)°. Crystals of (III) are also monoclinic, space group P2₁/c, with a= 5.49(1), b= 15.52(1). c= 10.81 (1)Å, β= 105.9(1)°. The structures were solved by the heavy-atom method and atomic parameters were refined by full-matrix least-squares calculations to R 0.047 (I), 0.044 (II), and 0.072 (III) over 1 129, 1 594, and 1 241 statistically significant reflections. In all three molecules the dithian rings adopt chair conformations which are increasingly more puckered as the number of substituents increases. The C–S distances in (I) and (II) reveal interesting differences which depend upon the degree of substitution at the carbon atoms.