The conformation, aromaticity and gas-phase acidity (free energy of deprotonation, ΔGⅲ) of 1, 2-diselenosquaric acid (3, 4-dihydroxy-3- cyclubutene-1, 2-diselenone) 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- diselenosquaric acid presents a planar conformation. The ZZ isomer was found to be the most stable of the three planar conformers. The homodesmotic reaction aromatic stabilization energy (HASE) and magnetic susceptibility exaltation (Λ) were also computed by using the SCF-CSGT (Continues 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 HASE and Λ were more negative values, indicating that 1, 2-diselenosqaric acid is aromatic. Thus the titled compound fulfills the geometrical, energetic and magnetic criteria of aromaticity. The most reliable theoretical gas-phase acidity are ΔGⅲ ~1~(~2~9~8~K~)=1271.5kJ/mol and ΔGⅲ ~2~ (~2~9~8~K~)=1619.6kJ/mol.

Key words: SELENIUM COMPOUNDS, SQUARIC ACID, AROMATICITY, AB INITIO CALCULATION, ACID PROPERTY