A theoretical study of the dimerization of 1,2-dithia-4-cyclohexene (or 3,6-dihydro-1,2-dithiin), and its corresponding O, N and Se-substituted relatives

Computational studies have been carried out at DFT-B3LYP/6-31G** level of theory on the structural and spectroscopic properties and the dimerization of 1,2-dithia-4-cyclohexene (T, or 3,6-dihydro-1,2-dithiin), and its relatives, 1,2-diselena-4-cyclohexene (S, or 3,6-dihydro-1,2-diselenine), 1,2-dioxa-4-cyclohexene (O) and 1,2-diaza-4-cyclohexene (A). The optimized geometries of the monomers and dimers and their bonding characteristics, and IR and NMR spectra, as well as thermodynamic properties have been calculated and analyzed. The results of this study show that the dimer of S is more stable than its monomer, partly due to the less bond angle strains. This is while thermal dimerizations of S, O and A are not favored at STP. The optimized geometry for the dimer of T is in excellent agreement with the solid state X-ray data. The poor agreement between experimental and calculated NMR chemical shifts for T is probably due to the gas-to-liquid shifts and solvent effects. Dimerization of these compounds proceeds via the cleavage of their heteroatom-heteroatom bond.