  The ring-coalescence and annealing model for fullerene formation postulates a [2+2] cycloaddition of polyynes to produce a polyethynyl-substituted cyclobutadiene which then undergoes a Bergman cyclization to produce a p-benzyne.  Computationally, the cyclization of diethynylcyclobutadiene proceeds in the expected manner and is slightly exothermic, but the subsequent ring-opening to produce cyclooctadiendiyne has a vanishingly small barrier.  The diradical will thus be short-lived, which appears to be inconsistent with the current model.

Model studies for elementary steps in carbon condensation mechanisms

243rd National Meeting (2012)

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