The effect of methyl substitution on the electronic structure and spectra of benzyl-type radicals

The effect of methyl substitution on the electronic properties of the benzyl radical has been studied by spectroscopic as well as theoretical methods. The polymethylbenzyl radicals were produced from solid state photolysis of the corresponding methylbenzenes dispersed in n-hexane at 77 degrees K. The energies of the first and third excited doublet states of each radical were determined from the 0, 0 bands or their fluorescence (around 5000 angstrom) and UV excitation (at about 3300 angstrom) spectra. respectively. In addition, these energies were calculated using an SCF MO method with configuration interaction, the participation of the methyl groups to the pi-electron system being introduced by the concept of hyper-conjugation. Correlations between spectroscopic and theoretical data are discussed, particularly in cases where the parent molecules give rise to several isomeric radicals.