Elementary Steps Associated with Addition and Elimination Reactions

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The Organic and Macromolecular Chemistry Program supports the research of Drs. Heinz and Judith Koch, which aims at an experimental study of those electronic factors that influence 1,2-elimination reactions. The base induced elimination of a hydrogen and a leaving group (x) from an adjacent carbon is a very complicated process that has relevance to both biological and industrial chemistry. The reverse process, the addition of HX across a double bond is also a major reaction in organic chemistry and an understanding of its various mechanisms is an important topic worthy of study. More specifically, proton-transfer reactions between carbon and oxygen will be studied and compared to ejection of halide from carbanion intermediates that are generated in alcoholic alkoxide solutions. Reactions of saturated haloalkanes with alkoxide result in proton transfer from carbon to oxygen to form a hydrogen-bonded carbanion with a beta-halide. The anion can be neutralized by either a loss of the beta-halide to form an alkene, or transfer of the proton back to carbon (internal return). The latter is a no-reaction process, but it can be detected by the study of primary kinetic isotope effects of hydrogen associated with the elimination reaction. A third reaction would lead to a new carbanion that is free of contact stabilization. If that anion is neutralized prior to halide loss, the process can be detected by using a deuterated alcohol as solvent. Both alpha and beta-carbon isotope effects associated with the eliminations will also be measured. Reactions of fluorohaloalkenes with alkoxide generate a free carbanion directly. If reaction occurs in alcohol there is a competition between loss of halide or protonation to neutralize the anion. Chemistry of carbanions generated by both methods will be compared.