Gas-phase acidity and aromaticity of 1,2-dithiosquaric acid

The conformation, aromaticity and gas-phase acidity (free energy of deprotonation, Delta G(-)) of 1, 2-dithiosquaric acid (3, 4 -dihydroxy-3-cyclubutene-1, 2-dithione) were calculated at the SCF and MP2 and B3LYP levels using 6-311G(d, p) and 6-311+G(d, p) basis sets. The global minimum found on the potential energy surface of 1, 2-dithiosquaric acid presents a planar conformation. The ZZ isomer was found to be the most stable one of the three planar conformers. The aromatic stabilization energy (E-AS) and magnetic susceptibility exaltation (Lambda) were also computed by using the homodesmotic reaction and RHF-CSGT (Continue set of Gauge Transformations) (IGAIM, a slight variation on CSGT) and B3LYP-CSGT(IGIAM) methods at the 6-311+G(d, p) level. The calculated EAS and were more negative values, indicating that 1, 2-dithiosqaric acid is aromatic. Thus the titled compound fulfilled the geometrical, energetic and magnetic criteria of aromaticity. The most reliable theoretical gas-phase acidity are Delta G(298.1)(-) = 1278.2 kJ.mol(-1) and Delta G(298.1)(-) = 1648.5 kJ.mol(-1).