Electronic Spectra and Electron Affinity of Monomethyl- and Dimethyl-Substituted Benzyl Radicals

Article abstract of DOI:10.1021/j100438a015

Three monomethylbenzyl radicals and five dimethylbenzyl radicals have been authentically generated by the dissociative electron attachment to corresponding methyl-substituted benzyl chlorides in γ-irradiated glassy matrices and studied by the fluorescence spectrophotometric method at 77 K.For the radicals in a polar ethanol matrix where they are free from the chloride counterion, the wavelengths for the O-O bands of the fluorescence spectra and of the fluorescence-excitation spectra (to the third excited state, in 320-330-nm region) have been determined.These results revise the previous assignment of the spectra of 2,4- and 3,4-dimethylbenzyl radicals.In a nonpolar 3-methylhexane matrix, the association of the counterion with the radicals causes the change in vibrational structures, as well as the shifts of the spectra due to the radicals, and the appearance of a charge-transfer band due to the chloride ion-radical pairs.From the transition energies of the CT bands, the electron affinities have been determined for all eight methyl-substituted benzyl radicals with reference to the reported electron affinity of the benzyl radical.These experimental electron affinities are in general agreement with those calculated theoretically within the INDO approximation.It has been also found that the photolysis of substituted and unsubstituted benzyl chlorides at 77 K results in the rupture of a C-H bond as well as a C-Cl bond, so that several isomeric benzyl-type radicals are generated simultaneously.