International Collaboration in Chemistry: Is the Single Transition State Model appropriate for the Fundamental Reactions of Organic Chemistry?

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).The Organic and Macromolecular Chemistry Program in the Chemistry Division at the National Science Foundation supports a proposal from Professor Vernon D. Parker of Utah State University. This proposal, submitted in response to solicitation NSF 08-602: International Collaboration in Chemistry between US Investigators and their Counterparts Abroad (ICC), is a collaboration with Professors Xiao-Qing Zhu and Jin-Pei Cheng of Nankai University in China. The research team will focus on a research project in physical organic chemistry with profound importance for mechanistic organic chemistry. The scientific objective of this proposal is to provide an answer to the question; "Is the single-transition state model appropriate for the fundamental reactions in organic chemistry?" The basis for the question is that Professor Parker has presented preliminary evidence that several fundamental organic reactions including C-H proton transfer reactions, hydride exchange reactions, carbenium ion-nucleophile combination reactions, neutral-anion and neutral-neutral combination reactions, SN2 reactions as well as the classical E2 elimination reactions take place by a 2-step mechanism. The 2-step mechanism is designated as the "kinetically significant pre-association mechanism" to distinguish it from pre-association mechanisms which cannot be kinetically differentiated from the single-step mechanism. The PI's preliminary non-steady-state kinetic methods including "instantaneous rate constant analysis" and his hypothesis that the single-transition state model is not generally appropriate for the fundamental reactions of organic chemistry, have not gained general acceptance by the physical organic chemistry community. A new and extremely simple kinetic isotope effect (KIE) mechanism probe has been developed, which unambiguously differentiates between 1-step and the kinetically significant pre-association reaction mechanisms. Thus the new method differentiates between the mechanisms and evaluates KIE for the kinetically significant pre-association mechanism without the need to evaluate any rate constants. Detailed studies of six different fundamental reaction types are proposed. The broader impacts are enormous and range from the outstanding training students will receive at both universities to having a large impact on the field of physical organic chemistry. The overall impact is that this international project will foster cooperation and good will between the scientific communities of the United States of America and the People's Republic of China. This project will contribute to the National Science Foundation's effort to fund training of a diverse, globally-engaged, U.S. science workforce.