With this Renewal Award, the Chemical Structure, Dynamics, and Mechanisms Program continues to support Professor Scott Gronert of Virginia Commonwealth University in a project involving investigations of organic reaction mechanisms in the gas-phase using mass spectrometric methodologies. The studies will be focused in two major areas. In the first, important catalyst systems will be examined with goals of understanding their mode of action and developing approaches for optimizing their selectivity. Specifically, the formation and reactivity of metal/carbene systems will be explored and a new, general method for screening the stereoselectivity of metal-centered, Lewis acid catalysts will be developed. In the second component of the overall project, the factors that control the rates and the selectivities of substitution and elimination reactions will be explored. Specifically, the effect of substituent groups on the rates and products of nucleophilic aromatic substitution reactions will be determined and the regioselectivity and stereoselectivity of elimination reactions will be characterized. For all of these studies, the central hypothesis is that the gas-phase reactivity patterns will generally parallel those observed in solution and offer an alternative means of investigating the processes. The rationale for this work is that by using gas-phase studies, the bonding characteristics of specific, isolated intermediates can be probed, thus, gaining mechanistic information not readily available from experiments in the more complicated condensed phase environment. This information can be highly valuable in the future development of applications employing these reactions.
This research, to understand gas phase reactivity patterns and show how these will generally parallel those observed in solution, has implications for understanding the mechanistic pathways of many important chemical reactions. These studies are ideally suited for training undergraduate researchers and potentially recruiting them into advanced degree programs. Outreach efforts will include recruiting trips to local colleges and universities with large under-represented populations as well as the direct recruiting of at least one student per year from Virginia Union University (a local HBCU) for a summer research experience in the PI's lab. The PI's research program has traditionally attracted a diverse group of students (currently three from under-represented groups and five women) and outreach efforts will be aimed at enhancing diversity in the group and the department. The PI has had success incorporating undergraduates into meaningful research experiences in the past and will actively recruit them for these studies.
During the grant period advances were made in the development of technology, the discovery of new scientific results, and the development of human capital in STEM fields. The major technical advance was the design, construction, and validation of a variable-temperature, quadrupole ion trap mass spectrometer. This device allows chemists and physicists to study gas- phase ion reactions at multiple temperatures. There are potential applications in atmospheric science, materials development, and the design of new chemical reactions. Currently, it is being used to develop an understanding of what factors control the distribution of products in fundamental organic chemistry reactions. Scientific advances were made in the study of catalysts that can be used in the synthesis of fine chemicals and pharmaceuticals. Our goals were to uncover the key reactive intermediates that are involved in the catalytic cycle and develop rules for understanding structural elements that enhance or reduce their efficiency in cyclopropanation reactions. Surprisingly, we discovered that the accepted intermediates did not have the appropriate characteristics to participate in the catalytic cycle. This led us to propose new intermediates and opens the door to designing more effective approaches in the synthesis of important chemicals. In addition, we probed the mechanism of nucleophilic aromatic substitution processes and developed new guidelines for predicting products in this fundamental and synthetically useful reaction. Student training was a major goal as a broader impact. The effort included a focus on undergraduates and members of under-represented groups. A total of 11 students were trained, including 7 undergraduates. The research effort also included 5 contributors from under-represented groups. A key part of the effort was recruiting a student each summer from a local HBCU to participate in a research experience in the group.
