Analysis of ESR Spectra Observed in Irradiated Aromatic Systems

Several structures have been proposed to explain the large hyperfine splittings observed in aromatic systems which have been exposed to ionizing radiation or hydrogen-atom bombardment. The observed extra hyperfine structure was used to obtain electron densities on the various carbon atoms of the cyclohexadienal radical, and McLachlan's treatment was applied to calculate the splitting of the two hydrogen atoms on the single carbon atom of the C6H7 radical. The calculated values are in satisfactory agreement with the 45- to 50-G splitting between lines of the observed triplet. The other proposed structures are shown to be unlikely to produce such large splittings, or not applicable to purely aromatic systems.