Edge Migration of Aromatic Rings by Radical ReactionsKinetics and Directionality

A series of five- and seven-ring migration reactions
of polyaromatic
radicals were examined theoretically. Computed reaction energetics
and rate constants demonstrate the facileness of such migrations.
The results show, however, that the direction of migration is not
identical for homologous reactions. It is determined by strain-induced
changes in molecular geometry, which is confirmed by the harmonic
oscillator model of aromaticity analysis. One of the notable outcomes
of the present study is that fused five-membered rings can form, not
split, thereby challenging the isolated pentagon rule.