Thermal Isomerizations of Diethynyl Cyclobutadienes and Implications for Fullerene Formation

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• 作者：Brian J. Esselman ; Frank L. Emmert III ; Andrew J. Wiederhold ; Stephanie J. Thompson ; Lyudmila V. Slipchenko ; Robert J. McMahon
• 刊名：Journal of Organic Chemistry
• 出版年：2015
• 出版时间：December 4, 2015
• 年：2015
• 卷：80
• 期：23
• 页码：11863-11868
• 全文大小：386K
• ISSN：1520-6904

文摘

The mechanism by which carbon condenses to form PAHs or fullerenes is a problem that has garnered considerable theoretical and experimental attention. The ring-coalescence and annealing model for the formation of C₆₀ involves a [2 + 2] cycloaddition reaction of a cyclopolyyne to form a tetraalkynyl cyclobuta-1,3-diene intermediate, followed by a Bergman cycloaromatization reaction of the enediyne moiety. Intramolecular trapping of the incipient p-benzyne diradical across a diyne moiety of the macrocyclic ring affords an aromatic ring that must undergo further intramolecular reactions via polyradical intermediates to produce a condensed graphitic structure or fullerene. Computational studies of a model system for the intriguing tetraalkynylcyclobuta-1,3-diene intermediate, however, reveal that the corresponding p-benzyne diradical lies in a shallow minimum with a very low barrier to ring opening to cyclooctadienediyne. This pathway has not been previously considered in the mechanism for carbon condensation.