About the benzotriazole tautomerism:: an ab initio study

The tautomeric equilibrium of benzotriazole was investigated using Hartree-Fock (HF), MP2, B3LYP and coupled cluster methodologies with a series of basis set. The HF and MP2 results present a clear preference for the 1H and 2H tautomers, respectively, while with B3LYP and coupled cluster both structures have a very similar energy. The inclusion of zero point energy was proved to be necessary when using B3LYP and coupled cluster methods, leading to a preference for the 1H tautomer. The geometric parameters obtained with MP2 and B3LYP using aug-cc-pVTZ basis set are very similar to experimental data of I H. The frequencies also provided a great concordance with experimental data with the correct use of scale factor. Dipole moment and rotational constants were also analysed. (C) 2003 Elsevier B.V. All rights reserved.