Conformational analysis of extracted natural dithiins from garlic and onion: a computational study

Optimized geometries and energies for conformations of 4H-1,2-dithiin, 3-vinyl-4H-1,2-dithiin, 4H-1,3-dithiin, and 2-vinyl-4H-1,3-dithiin were calculated using the HF/6-31+G*, B3LYP/6-31+G*, and MP2/6-31+G* levels of theory. In each of them, three energy minima and two transition states were found. The results indicated that twisted forms corresponded to all the above molecules were the most stable conformers than their other conformers (as global minimum). The boat forms related to each of them were observed as local minimum. The results showed that the twisted forms had more stability than the related boat forms. The half-chair conformers for each molecule were attributed to the transition state forms. The half-chair forms were calculated to be 12.4-23.9 kJ mol-1 less stable than their twisted conformations.