Organic Free Radical and Electron Transfer Chemistry

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This grant within the Organic Dynamics Program represents a continuation of the work by Martin Newcomb of Texas A&M University. The aim of this project is to elucidate the pathway of organic reactions which involve free radicals or radical anions. This work is quite significant in that it will investigate many reactions suspected to proceed by the pathway known as SET (single electron transfer) which have previously been considered to react by other mechanisms. This will enhance knowledge about how organic reactions proceed, and, therefore, how they can be improved. Continued studies in the areas of organic free radicals and mechanisms of potential electron transfer processes in organic reactions will be investigated. Kinetics of exceedingly fast carbon radical rearrangemens will be studied by the PTOC/thiol method developed in the Texas A&M laboratory with the objective of calibrating radical clocks so fast that they may be used in competition with diffusion-controlled second order processes in non-viscous solvents. In the PTOC/thiol method, N-hydroxypyridine-2-thione esters are employed as radical precursors and thiophenol is used as a radical trapping agent, and reactions with first order rate constants in excess of 1 x 10exp-9/s at 25 degrees C can be calibrated. Aminyl and aminium cation radicals from N-hydroxpyridine-2-thione carbamates will also be studied. The main objective will be to determine the rate constants for simple second order reactions (such as hydrogen atom transfer) of these intermediates; with basis reaction rate constants available, nitrogen-centered radical clocks will be calibrated. Potential electron transfer processes (especially in reactions of lithium dialkylamides) will continue to be studied. Verification of the experimentally derived oxidation potential for the dialklamide anion--dialkylaminyl radical couple will be sought. Reactions of lithium dialkylamides with trityl halides will be studied; recent results suggest that a previously unconsidered reaction process may be operating in this case.