At high temperatures, benzene ring contractions and 1,2-shifts contribute to the formation and interconversions of PAHs, but the mechanism for such reactions remains unclear.  We report computational results on the detailed mechanisms of  rearrangements reported by Vollhardt and coworkers, including benzene, biphenylene, angular [3]phenylene and other systems. The carbene-based processes generally occur in two steps, with barriers of 80 kcal/mol (biphenylene) to 96 kcal/mol (benzene) obtained at the CCSD(T)/cc-pVDZ//B3LYP/6-31G* level. The relatively low barrier for biphenylene arises from the release of ring strain. The computational results from smaller systems were used to analyze more complicated mechanisms involved in the rearrangement of angular [3]phenylene (69.9 kcal/mol).

Polycyclic aromatic hydrocarbon rearrangements under high temperature and flash vacuum pyrolysis

245th National Meeting (2013)

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