The tautomers (E1, E2, E3, E4, and K) and the ground state intramolecular proton transfer reaction of 2-(2-mercaptophenyl)benzoxazole were studied at the B3LYP/6-31G(d,p) level. The effect of solvent (water, dimethylsulfoxide, acetonitrile, ethanol, aniline, and cyclohexane) was studied at the B3LYP/6-31G (d,p) level, using the polarizable continuum model. The results of density functional calculations indicate that the enol form E1 is the most stable tautomer at the ground state. In these solvents there is an equilibrium for 2-(2-mercaptophenyl)benzoxazole in the ground state between E1 and K, and the equilibrium shifts toward the tautomer K as the polarity of the solvent increases. E1 is the preferential conformation in cyclohexane, but K is the more stable tautomer in water.

Key words: 2-(2-mercaptophenyl)benzoxazole, intramolecular proton transfer, density functional theory, polarizable continuum model