The results of valencehyphen;bond spinhyphen;density calculations for a number of positive (+) and negative (mdash;) aromatic ion radicals are given. For naphthalene, it is found that the agr; and bgr; position spin densities in the positive ions do not equal those in the negative ion; that is (rgr;agr;(+)/rgr;agr;(minus;)) = 1.01 and (rgr;bgr;(+)/rgr;bgr;(minus;)) = 0.933. This result, which contrasts with that of molecularhyphen;orbital calculations, may provide a partial explanation of the small hyperfine splitting differences found in (+/mdash;) ion pairs. It is noted that for a number of ion radicals, predominantly positive ions, the symmetries of the ground state, as predicted by the valencehyphen;bond and molecularhyphen;orbital methods, are not the same. Although these symmetry disagreements introduce only small changes in the spin densities of most of the molecules studied, the azulene positivehyphen;ion results may be sufficiently different to permit an ESR test of the theories. Other experiments and calculations which would also be important for evaluating the valencehyphen;bond method for ion radicals are discussed.
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