This grant in the Organic and Macromolecular Chemistry Program supports research by Dr. Przemyslaw Maslak aimed at elucidating the factors which control carbon-carbon bond cleavage reactions in a group of reaction intermediates known as ion radicals. Ion radicals are unique and reactive species which have complex and not yet well understood properties by virtue of having some of the characteristics of ions (electrical charge) and some of the characteristics of radicals (unpaired electrons) at the same time. Radical ions are increasingly recognized as an important class of reaction intermediates as chemists learn of more chemical reactions shown to occur via electron transfer mechanisms. Specifically, Dr. Maslak's research is aimed at providing quantitative measurements of the thermodynamic and kinetic parameters controlling these bond cleavage reactions. The investigation concentrates on the electron apportionment aspect of the cleavage reaction of radical ions wherein the odd-electron density is highly localized on one side of the scissile bond. It is thought that localization of the spin density on the same part of the molecule throughout the reaction is kinetically advantageous, even if it leads to thermodynamically less stable products. This research will explore the validity of such a spin regioconservation rule. The experimental distinction between the two possible ways in which electrons are apportioned to the fragments will be accomplished by linear free energy relationship studies and by trapping of the primary fragmentation products. Another approach will use especially designed molecules in which electron apportionment is reflected in the regiochemistry of the cleavage reaction. The influence of ion pairing and solvation on the fragmentation reactions will be probed by variation of solvent polarity and gas-phase studies. The results of this work may have practical value for improving processes based on electron-transfer catalysis, which are important in synthesis, solar energy conversion, coal liquefaction, and other areas.
