Hydrogen-mediated Stone-Wales isomerization of dicyclopenta[de,mn]anthracene.

The mechanism of transformation of two radicals (R1p and R1i) obtained by addition of a hydrogen atom to an external and internal carbon atom of dicyclopenta[de,mn]anthracene (P1) was investigated. Two pathways were revealed. The first mechanism is a one-step process, whereas the second mechanism includes two transition states and a cyclobutyl intermediate. The formation of R1p and R1i and the homolytic cleavage of the radicals obtained during the isomerization processes were also examined. In both pathways the addition of a hydrogen atom to the internal carbon significantly lowers the activation energy for hydrogen-mediated isomerization of P1 to acefluoranthene. This finding could be explained by the specific electronic structures of the transition states and intermediates participating in the isomerization processes.