Electronic Structures of Aromatic Ketyl Radicals and Related Hydrocarbon Radicals

Abstract The π-electron structures of neutral aromatic ketyl radicals and their related hydrocarbon radicals were studied theoretically by combining the open-shell SCF MO method with the configuration-interaction calculation. The observed absorption bands of these radicals were well explained by the present theoretical study. From a comparison of the calculated transition energies and intensities with the observed values, it was concluded that the longest and second longest wavelength bands of the benzyl radical and the second longest wavelength band of the diphenylmethyl radical shift to shorter wavelengths upon hydroxy substitution. This may be regarded as characteristic of the substituent effect upon the absorption bands of aromatic radicals. The calculated spin densities were found to be consistent with the reactivity of the ketyl radicals in the formation of pinacols.