Electronic structure study of thermal intraconversions of some dicyclopenta-fused polycyclic aromatic compounds

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.

Formation and isomerization of dicyclopenta[de,mn]anthracene. Electronic structure study

The formation of dicyclopenta[de,mn]anthracene (P1) and its isomerization into dicyclopenta[jk,mn]phenanthrene (P3) was investigated using density functional theory. It was shown that P1 is formed from 1,4-diethynilanthracene, but due to its instability, it undergoes further transformation. This transformation involves rearrangements of some hydrogen atoms and ring contraction/ring expansion process, yielding as a final product the isomer P3. The energies of activation for the P1-->P3 intraconversion show that this reaction is competitive to the other, previously investigated isomerization of P1 into dicyclopenta[de,kl]anthracene (P2). In addition, our investigation shows that the formation of P3 from P1 is energetically more favorable than the formation of P3 from P2. Thus, the presence of the isomer P3 in the reaction mixtures could also be caused by the isomerization of the very unstable isomer P1.