The Chemistry of -Oxo Ketene Cyclic Dithioacetals Xⅳ. The Stability and Characters of 1,1-（1,3-Dithiopropylidene）-3,4-diphenyl -1,3-dibutene

The structures of the title compounds were studied with quantum chemistry semi-empirical MNDO method. By calculation, it was shown that, similar as the experimental results, the two isomers of the title compounds of 4a and 5a are stable, 4a has lower system energy than 5a.Comparing with determination values, the structures of the title compounds were established via calculation. In two isomers, same as shown by the UV value of 4a and 5a, the two phenyl groups were not conjugated with the diene system.