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 shifted toward the 2H tautomer in the gas phase (Delta E(1H-->2H) = similar to-4 kcal mol(-1)) can only be reproduced theoretically if electron correlation is introduced during the geometry optimization (MP2-6-31G**). The geometries obtained at this level yield excellent rotational constants, and the associated charges explain the different vectorial components of the experimental dipole moment, a result that 6-31G** geometries cannot afford. Recept spectroscopic data obtained for benzotriazole in the gas phase, interpreted assuming that the major tautomer is the 1H-benzotriazole, were reanalyzed to show that they can be explained considering a mixture of both tautomers and its dependence with temperature.