Optical anisotropies of methyl benzoate and diesters of benzenedicarboxylic acids as determined from the analysis of Kerr constants and depolarized light scattering measurements

Abstract

Mean-square optical anisotropies of methyl esters of benzoic, terephthalic, isophthalic and phthalic acids have been measured at T= 25°C by analysis of the depolarized Rayleigh spectra of their dilute solutions in CCl₄ and CHCl₃. A planar Fabry–Perot interferometer was used to record the spectra and the VH spectrum of benzene was used as standard. The experimental values thus obtained were 〈γ²〉= 46, 136, 97 and 58 Å⁶ respectively, for methyl benzoate, dimethyl terephthalate, dimethyl isophthalate and dimethyl phthalate. The analysis of these experimental results, together with values of Kerr constants of the same molecules taken from the literature, allows the formulation of the anisotropic part of the optical polarizability tensors of phenyl and ester groups, including the inductive effects produced when these groups are linked together. The results seem to indicate that the inductive effects do not depend on the number of ester groups or the positions by which they are attached to the benzene ring; however they are very sensitive to whether both groups are coplanar.