Ab initio molecular orbital theory at the STO-3G level is used to elucidate the structures and relative abundances of stable conformations of the three benzenedicarbaldehydes. In addition, new measurements of the infinite-dilution dipole moments and molar Kerr constants of these molecules as solutes in dioxan at 25�C are reported and analysed. The previously recognized inability of the simple group- additivity model to reliably predict the anisotropy in the polarizability of benzene-1,4-dicarbaldehyde is shown to be due to a redistribution of the polarizability in the molecular plane.

Experimental dipole moments and infinite-dilution molar Kerr constants are reported for six p-substituted acetophenones (CH3COC6H4X; X = Me, But, NO2, CN, F, Br) as solutes in carbon tetrachloride at 298 K. Analysis of these results and reconsideration of previously reported data for acetophenone and p-chloroacetophenone yields the dihedral angle, Φ, between the planes of the carbonyl and aryl groups in the effective conformation of each molecule (X = H, Φ = 0°; Me, 0°; But, 10�10°; NO2, 20�15°; NO2, 20�20°; F, 27�5°; Cl, 32�5°; Br, 30�10°).

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