Ab Initio Calculations on Proton Transfers

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9313657 Saunders Proton transfers from acids in which the ionizing proton is attached to carbon will be studied by quantum chemical methods. The energies and other properties of the separated reactants, the ion-dipole complexes, and the transition state structures for proton transfer will be calculated for a number of carbon acids that yield delocalized anions of the sort widely used in organic synthesis. A study will also be made of a prototype for oxygen acids that yield delocalized anions, acetaldehyde enol, and a comparison will be made to the carbon-centered acid, acetaldehyde. The aim of the research will be to explore the factors that influence barriers to proton transfer: acidity, heavy-atom reorganization, charge transfer, and polarizability. These gas-phase calculations will be compared to literature experimental results in both the gas-phase and solution. Calculations of isotope effects will be done on selected systems, including deprotonation of propene by hydroxide ion and elimination reactions in order to establish what level of calculation is necessary to give reasonable isotope effects, and to compare the results with experimental data in solution. %%% This grant from the Organic Dynamics Program supports the work of Professor William H. Saunders at the University of Rochester. The transfer of a proton from an acid is one the most common and most important reactions in chemistry. This work will study proton transfers reactions by computational methods and compare the results to experimental data. The individual factors that control the energy barrier to proton transfer will be probed in these calculations. Deuterium substitution, which alters the rate of proton (or deuterium) transfer and is important in determining the mechanism of proton transfer, will be calculated and compared to experimental results. ***