Ab initio study of 1,2-dithiosquaric acid

Result of ab initio SCF calculation of 1,2-dithiosquaric acid (3,4-dihydroxy-3-cyclobutene-1,2-dithione) are reported. The ZZ isomer is found to be the most stable of the three isomers. An isodesmic energy analysis has been carried out at the HF 6-31G*//6-31G* level for the three planar isomers. The three isomers have positive isodesmic energies or small negative ones, suggesting that 1,2-dithiosquaric acid is not aromatic. Vibrational frequencies have also been calculated for the three isomers.