Ab initio and density functional study of the geometrical, electronic and vibrational properties of 2,2?-bipyridine

The conventional ab initio method at the closed restricted Hartree–Fock level (RHF) and the Density Functional Theory (DFT) approach at the B3-LYP level, using the 6–31G(+*) basis set, are applied to predict the molecular structure and the energetic and vibrational properties (harmonic wavenumbers, force fields and potential energy distributions) of five isotopomers of the neutral molecule 2,2′-bipyridine (22BPY). The theoretical results are compared to the Raman and infrared vibrational data. Using both methods, there is a very good agreement between theory and experiment concerning not only the absolute wavenumbers, but also the isotopic shifts. This accordance allows us to validate the calculated structure of 22BPY. The neutral molecule 22BPY is characterized by an aromatic structure in which two pyridyl rings are linked by a single bond in a trans-planar conformation. From a methodological point of view, the B3-LYP method predicts more accurate structures and harmonic vibrational wavenumbers than the RHF method.