EPR-SPECTRA AND STRUCTURE OF THE RADICAL CATIONS OF FLUORINATED BENZENES

EPR spectra for the radical cations of a series of fluorinated benzene s, generated by irradiation with gamma-rays in halocarbon solid matric es, have been observed at low temperatures. The spectra consist of a h yperfine structure with axially symmetric anisotropy mainly due to flu orine nuclei. The observed spectra have been analysed by simulation. A b initio calculations have been conducted for the cation radicals to o btain their optimized geometries. The results reveal that an unambiguo us deformation in geometry is brought about by cationization in each c ase. INDO calculations have been performed for-the optimized geometrie s of these radical cations to calculate the hyperfine couplings. The c alculated couplings strongly support the observed ones. The symmetry o f the SOMO for the radical cations resembles that of the HOMO of their neutral mother molecules. The deformed geometries of these radical ca tions suggests that in the process of releasing an electron from an HO MO, those chemical bonds with bonding nature in the HOMO become elonga ted and those bonds with antibonding nature become shortened. It is co ncluded that the structure and symmetry of the SOMO of these radical c ations are affected not only by the number of substitutions by fluorin e but also by the position of substitution.