The Chemical Structure, Dynamics, and Mechanisms Program supports Professor Nancy S. Mills at Trinity University whose proposal describes the evaluation of the antiaromaticity of indenylidene dications through changes in the placement of substituents and changes in the manner in which the ring systems are linked together. The extension to indenyl systems has the potential to provide antiaromatic species with a broader range of antiaromaticity because the indenyl cation has been shown to be more antiaromatic than the fluorenyl cation. In addition, the local antiaromaticity of the 5-membered ring can be probed through 1H NMR shifts, and its inherent antiaromaticity varied through substitution on the 5-membered ring. These two approaches are not possible for the fluorenyl system whose central 5-membered ring possessed neither protons to be used as a probe nor the possibility of substitution. The opportunity to examine the effect of substituents on both 5-and 6-membered rings in the indenyl system, coupled with the potential for enhanced antiaromaticity of an indenyl system makes this an exciting system for examination. Extension of the investigations of antiaromatic hydrocarbon dianions to the dianion of di-and tribenzannulated heptafulvalene and to antiaromatic heterocyclic dianions is also proposed.

With the support of the Chemical Structure, Dynamics, and Mechanisms Program in the Chemistry Division at the National Science Foundation, Dr. Mills' research will study aromaticity, a key concept in organic chemistry. This study will help to explain the stability of chemical compounds and guide the design of new molecules. Trinity University has an active undergraduate research program that emphasizes the early exposure of undergraduates to research. Students will be exposed to the theory that explains the key concepts of aromaticity and see how these are validated by experimental observations. In addition, the research will help support the activities of a research/teaching post-doctoral associate, patterned after the Dreyfus Scholar/Fellow program. Because Trinity University has a relatively large cohort of research /teaching post-doctoral fellows, currently four in chemistry, the department is able to implement a series of activities designed to prepare this group for successful academic careers at principally undergraduate institutions (PUIs).

Project Report

The understanding of factors that affect the stability of molecules is extremely important to chemists because stability dictates the kinds of molecules that can be synthesized. For an organic chemist, one who deals with compounds that are based on carbon, molecules that are considered "aromatic" are very stable, and are often found in nature because of that stability. The theory that explains their stability also predicts that there are compounds that would be particularly unstable. Because these compounds are the antithesis of aromatic compounds, they are known as antiaromatic compounds. These compounds are very poorly understood because no one tried to prepare them because their instability was assumed to make them very hard to characterize. Through a fortuitous experiment that went awry, the Mills research group has been able to prepare dozens of antiaromatic ions, and to use their antiaromaticity to better understand stability, primarily because antiaromatic ions exhibit some of the properties seen in aromatic compounds much more dramatically. These discoveries are even more remarkable because they were made primarily by dozens of undergraduate researchers from Trinity University. With support from the National Science Foundation, as well as other sources, between 9 and 13 students each summer prepare the precursors to the antiaromatic dications and dianions, in addition to converting them into the antiaromatic species. Students working in the lab have become research scientists, medical doctors, and teachers in high school, community college, and four-year colleges. Their research experience has deepened their understanding of science in a way that is much more effective than is often found though class work.

National Science Foundation (NSF)
Division of Chemistry (CHE)
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Tyrone D. Mitchell
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Trinity University
San Antonio
United States
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