RUI: Heavy-Atom Tunneling in Annulenes and Helical Polycyclic Conjugated Hydrocarbons

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With this award, the Chemical Structure, Dynamics and Mechanism Program of the NSF Chemistry Division is supporting Professor William Karney and his undergraduate research team in the Department of Chemistry at the University of San Francisco to explore the extent of quantum mechanical tunneling by heavy atoms in reactions of organic molecules. The project combines experiment and theory, and will contribute to a basic understanding of what types of chemical reactions proceed by passage through a barrier rather than over the barrier. Passage through the barrier is known as quantum mechanical tunneling. Systems to be studied include compounds with potential as molecular switches, and reactions relevant to organic synthesis and biochemistry. Students on the project will gain experience in synthesis, spectroscopy, and a wide range of computational chemistry methods. The highly diverse student population at USF translates to high potential for training members of underrepresented groups in science, especially women, Latinx students, and those from the Pacific Rim.Despite the large atomic mass of carbon relative to hydrogen, carbon atoms can tunnel through barriers in chemical reactions if they travel only short distances. This project combines experiment and computations to investigate heavy-atom tunneling in annulenes and polycyclic conjugated hydrocarbons. Low-temperature nuclear magnetic resonance spectroscopy will probe possible tunneling by all 16 carbons in the planar pi-bond shifting of [16]annulene. Transannular electrocyclic ring closures in several annulenes will be studied by multidimensional tunneling calculations to explore the scope of tunneling in pericyclic reactions. Orbital-symmetry forbidden electrocyclizations of helical polycyclic conjugated hydrocarbons, systems of potential use as chiroptical switches, will be computationally investigated, with a focus on tunneling and symmetry lowering due to excited-state mixing. The work seeks to deepen our understanding of heavy-atom tunneling and to broaden the scope of reactions studied in which tunneling plays a major role. The project also will provide training in synthesis, spectroscopy, and high-level computational techniques for undergraduates and includes outreach activities with local middle school students to expose them to computational chemistry.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.