In this project funded by the Chemical Synthesis Program of the Chemistry Division, Professor Mark Mascal of the Department of Chemistry at the University of California Davis will explore the fundamentals of molecular curvature and electronics by synthesizing organic polycycles that enclose volumes of space, from concave, to hemispherical, to completely closed shell bodies. The research program revolves around the triquinane molecular framework, a rigid, bowl-shaped, fused tricycle. Key features of synthetic interest are the oxidation of heterotriquinanes to nonplanar aromatic hemi-fullerene fragments, and the prospect of building out such structures into heterododecahedranes. The triquinane platform stabilizes chemical species that are normally seen only as reactive intermediates, such as tertiary oxonium salts, oxonium ylides, and tetravalent oxadionium ions.
In addition to the fundamental scientific impact, this project has the potential to contribute substantially to applied material science, in view of the continuing interest in curved aromatic surfaces in the area of nanotechnology. The broader impacts in terms of training and diversity lie in the program's interdisciplinary nature, encompassing at various points organic synthesis, noncovalent bonding, coordination chemistry, reactive intermediates, hypervalency, issues in aromaticity, crystallography, theoretical chemistry, and aspects of nanotechnology. Principal educational deliverables are the incorporation of research into undergraduate chemistry laboratory courses and the promotion of undergraduate research, particularly involving under-represented groups, through the involvement in dedicated, university-sponsored programs. Outreach involves participation in the ACS Project SEED, the UC Davis Youth Scholars Program, and the UC COSMOS program.
This research project involved the investigation of the chemistry of a molecular ring system known as heterotriquinane. The heterotriquinane ring system consists of three fused, pentagonal rings with a heteroatom, that is, an atom other than carbon, such as nitrogen (N), oxygen (O), or sulfur(S), in the central apex. The molecular structure is as shown in the first image, on the left. The fusion of these rings results in a puckered, trefoil shape, as shown in the first image, on the right, looking at the molecule edge-on. This project dealt largely with fundamental concepts in chemical bonding, in which heterotriquinane molecules were the objects of the investigations. Triquinanes are particularly useful for this purpose, since their rigid structure enables the observation of otherwise unstable bonding arrangements. The project gave insights into the nature of reactive chemical intermediates and new molecular species. Work of this kind advances fundamental science, the foundation upon which technological applications are built. Specifically, during this grant period we have been learning about how to better build outwards from the periphery of the heterotriquinane molecule in such a way that we can move towards a fully closed sphere, as demonstrated in the second image. Spherical molecules could be useful for the generation of products with novel material properties, for example, new high-performance plastics. The activities carried out under this grant also provided excellent opportunities for teaching and mentoring in science, and the inclusion of underrepresented groups, which constitute broader impacts of the research program. For example, one graduate student trained during this project was an African-American. The development of new educational materials was also undertaken by incorporation of research themes (chemical synthesis) into an undergraduate organic chemistry teaching laboratory. Finally, the research program also provided outreach in science and technology to young people, in the form of the COSMOS program (California State Summer School for Mathematics and Science), a summer residency program for high school students to learn science and research skills.
