An ab initio and DFT study of the valence isomers of pyridine

Ab initio (HF, MP2, and CCSD(T)) and density functional theory computed res ults on the equilibrium geometries, relative stabilities, strain energies, and vibrational spectra of the nine possible valence isomers of pyridine ar e reported. Although some aza-benzvalenes (V1N and V3N) lie lower in energy than Dewar pyridines (D1N and D2N), the strain energies for the latter are lower. Relative stabilities of the valence isomers, thermodynamic stabilit y. and skeletal rigidity are comparable to those of benzene valence isomers . (C) 2001 Elsevier Science B.V. All rights reserved.