Estimation of Inductive Effect PMO Parameters of Methyl & Ethyl Groups from Charge-Transfer Bands of Some π-Molecular Complexes

Abstract

The inductive effect PMO parameters of methyl and ethyl groups have been calculated from the trends in the chargetransfer bands of two series of π-molecular complexes; (i) of methyl- and ethyl-benzenes with iodine monochloride and (ii) of methylated thiophenes with tetracyanoethylene. Coulson-Longuet-Higgins perturbation technique has been applied to obtain expressions for the energies of the donor- MO's in terms of the Hiickel parameters of alkyl groups, and by correlating such expressions linearly with the longest wavelength CT-absorption bands of the molecular complexes, values of the Hiickel parameters of the alkyl groups have been determined. The calculated value for the methyl group is approximately the same for the two series studied and is close to the ones obtained by previous workers. The PMO parameter for ethyl group is found to be less than that for methyl group as expected, since inductive effect decreases with increase in chain-length of the alkyl group.