Reaction Trajectories at Nonstereogenic Atoms

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This grant in the Organic and Macromolecular Chemistry Program supports research by Prof. Peter Beak, University of Illinois, aimed at determining the trajectories of atomic motion during chemical reactions. Reaction trajectories may be considered among the most fundamental sorts of information to be derived about chemical reactivity, and knowledge of the geometrical arrangements of atoms in molecules has provided the basis for understanding molecular structure and its relationship to chemical reactivity. However, this work is directed towards determining geometries of transition structures involving nonstereogenic atoms, which heretofore have been unavailable. Dr. Beak and co-workers will investigate the trajectories for reactions at nonstereogenic heteroatoms by use of the endocyclic restriction test. In this approach, the geometry of the transfer of atom Z will be evaluated by investigations of systems in which the bond-forming atom X and the leaving atom Y are joined by a chain. The size of the ring required for a concerted endocyclic intramolecular reaction in the transfer of Z from Y to X limits the available reaction geometry. If the transfer has geometrical requirements which cannot be met intramolecularly, the reaction becomes intermolecular. These possibilities will be distinguished by double labeling, isotope effect, and kinetic experiments. Alternative mechanisms involving associative and dissociative steps will also be evaluated. Investigations of the geometries of reactions at oxygen, nitrogen, halogen, hydrogen and sulfur will be made. Other mechanistic probes, including substituent effects and structural rearrangements will be used to provide mechanistic information about these and related reactions.