Data on the number of resonance structures of free radical polycyclic conjugated hydrocarbons are tabulated and studied. The first examples of fluoranthenoid / fluorenoid and indacenoid polyradical systems are presented. Some comparative generalizations between benzenoid free radicals and fluoranthenoid / fluorenoid and indacenoid polyradical systems are formulated. For example, there is a tendency of these latter even-carbon nonalternant hydrocarbons to have fewer radical isomers compared to the former alternant hydracarbons. Examples where Fowler's leapfrog algorithm identifies the more stable fluorenoid anion and indacenoid dianion isomer are presented.
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