Abstract:We report high quality B3LYP Ab Initio studies of the electric dipole polarizability of three related series of molecules: para-XC 6 H 4 Y, XC 6 H 4 CH=CHC 6 H 4 Y and XC 6 H 4 N=NC 6 H 4 Y, where X and Y represent H together with the six various activating through deactivating groups NH 2 , OH, OCH 3, CHO, CN and NO 2 . Molecules for which X is activating and Y deactivating all show an enhancement to the mean polarizability compared to the unsubstituted molecule, in accord with the order given above. A number of representative Ab Initio calculations at different levels of theory are discussed for azoarene; all subsequent Ab Initio polarizability calculations were done at the B3LYP/6-311G(2d,1p)//B3LYP/6-311++G(2d,1p) level of theory.We also consider semi-empirical polarizability and molecular volume calculations at the AM1 level of theory together with QSAR-quality empirical polarizability calculations using Miller's scheme. Least-squares correlations between the various sets of results show that these less costly procedures are reliable predictors of <α> for the first series of molecules, but less reliable for the larger molecules.
SUMMARYWe report accurate ab initio studies of the geometries, electric dipole moments and dipole polarizabilities of azulene, fulvalene and naphthalene at both the Hartree Fock and density functional levels of theory. The molecular geometry was optimized in each case at the HF/6-311G(3d,2p) level of theory, and polarizabilities were then calculated at the same geometry but with the addition of diffuse Gaussian primitives.The BLYP density functional formulation was used for the density functional calculations. We also report semi-empirical (AM1, MNDO and PM3) electric dipole and dipole polarizability calculations for comparison; in each case the geometry was optimized before the properties were calculated. The semi-empirical polarizabilities give poor agreement with the ab initio values for the component of the tensor perpendicular to the molecular plane.The calculated mean polarizabilities of the title molecules, together with benzene and fulvene, have been decomposed into contributions from atoms and from groups of atoms.
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