Carbene, cyclobutyl, and potential diradical mechanisms were studied computationally for Stone-Wales rearrangements in several derivatives of as-indacene and pyracyclene, including cyclopent[hi]acephenanthrylene, dicyclopenta[cd,fg]pyrene, corannulene, diindeno[1,2,3,4-defg;1',2',3',4'-mnop]chrysene, and semibuckminsterfullerene. At the UM06-2X/cc-pVDZ and BD(T)/cc-pVDZ//UM06-2X/cc-pVDZ levels of theory, free energies of reaction reveal that transformations involving an increase in curvature are thermodynamically unfavorable. In addition, the carbene transition states or intermediates (corrected to 1000 °C) are generally around 100-120 kcal/mol higher than starting substrates, except for as-indacene (80 kcal/mol), which is the only process considered here that is predicted to have a barrier accessible under typical flash vacuum pyrolysis conditions.
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