Unpaired spin densities for a series of prototype heteroatom radicals (p-benzosemiquinone, o-benzosemiquinone, pyrogallolsemiquinone, and 2,5-dihydroxy-p-benzosemiquinone) are calculated using McLachlan's SCF theory with variation of MO parameters. Agreement with ESR hyperfine splittings is considerably improved relative to that obtained by means of Hückel MO theory.
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