Static Dipole Polarizability of o-,m- and p-Benzyne isomers: Ab initio,DFT and CCSD calculations

We report a study of the static dipole polarizability (α) of the o-, m- and p-benzyne isomers in their singlet ground state. Due to the biradical character of benzynes, calculations were performed at ab initio unrestricted Hartree-Fock (UHF) level of theory. The correlation effects were accounted for with second order Møller Plesset (MP2) method, Density Functional Theory (DFT) with the BLYP and B3LYP hybrid approaches and the coupled cluster CCSD method with 6-31+G(d,p) standard basis set with optimized geometries. C₂v symmetry restriction was employed for the geometry of o- and m-benzynes (closed and open conformation) and D₂h for p-benzynes (open and closed conformation). Because the high quality of the basis set is a requirement for accurate α determination, MP2 and DFT calculations were performed with the 6-31+G(d,p), the extended 6-311++G(3d,3p) and the specialized Sadlej basis sets. The CCSD calculations were only carried out with the 6-31+G(d,p) and the Sadlej basis sets. The results indicate that the average α polarizability values for o- and m-benzynes are lower than the corresponding to the experimental value of benzene, while this property for p-benzyne is slightly higher than the benzene one. The anisotropy Δα values of benzyne isomers are always higher than the anisotropy of benzene molecule. Finally, was found that the conformations of p-C₆H₄ are the less stable isomers, and are the most polarizables and anisotropic compounds from the benzyne series.