RUI: Computational Studies on Hydrocarbon Rearrangements: From Reactions of Polycyclic Aromatic Hydrocarbons to Tunneling in Annulenes

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The Chemical Structure, Dynamics and Mechanism-A Program of the NSF Chemistry Division supports the research of Professors Claire Castro and William Karney in the Department of Chemistry at the University of San Francisco. Professors Castro and Karney and their students are computationally probing reactions of hydrocarbons that occur over a wide range of temperature: from those that occur during combustion to those that occur at ambient temperature. One goal of this research is to elucidate feasible mechanistic pathways that explain experimental results. The high temperature reactions are relevant to the synthesis of materials such as carbon nanotubes; the lower temperature reactions are relevant to understanding the quantum chemical concept of heavy-atom tunneling, a fundamental aspect of chemical reactions. The project lies at the interface of organic, physical, and materials chemistry. This research is well suited for the education of undergraduate physical science students. The Castro/Karney team is also well positioned to provide education and training for students from groups that are underrepresented in science. Aromatic hydrocarbons undergo dramatic rearrangements at both high and low temperatures. At temperatures of 800-1200 °C, reaction types of interest include hydrogen transfers, Stone-Wales rearrangements, and vinylidene insertions. The computational study attempts to place the various reactions on a common theoretical footing to compare relative rates and generate a unified picture of reactivity for polycyclic aromatic hydrocarbons. The work also aims to clarify structure-reactivity relationships, for example, by evaluating how the degree of curvature influences the different mechanisms for Stone-Wales rearrangement. At lower temperatures, pi-bond shifting in annulenes is known to be facile, and the research explores the contribution of quantum mechanical tunneling. The possibility that large numbers of carbon atoms are tunneling simultaneously are explored by comparing classical and quantum tunneling rates. The work addresses the scope of tunneling in organic reactions. The educational plan includes training physical science undergraduates in computational methods and both physical and organic chemistry principles.