INFLUENCE OF LONE-PAIR REPULSION VS RESONANCE ENERGY ON THE RELATIVE STABILITIES OF MOLECULAR-STRUCTURES - A THEORETICAL APPROACH TO THE EQUILIBRIUM BETWEEN 1H-BENZOTRIAZOLE AND 2H-BENZOTRIAZOLE TAUTOMERS

The experimental conclusion that the tautomerism of benzotriazole is s hifted toward the 2H tautomer in the gas phase (Delta E(1H-->2H) = sim ilar to-4 kcal mol(-1)) can only be reproduced theoretically if electr on correlation is introduced during the geometry optimization (MP2-6-3 1G*). The geometries obtained at this level yield excellent rotationa l constants, and the associated charges explain the different vectoria l components of the experimental dipole moment, a result that 6-31G* geometries cannot afford. Recept spectroscopic data obtained for benzo triazole in the gas phase, interpreted assuming that the major tautome r is the 1H-benzotriazole, were reanalyzed to show that they can be ex plained considering a mixture of both tautomers and its dependence wit h temperature.