This grant in the Organic Dynamics Program provides support for the research of Dr. Fred Bordwell of Northwestern University. This work is divided into four areas: (1) the measurement of the acid strength of neutral and positively charged organic compounds, (2) the estimation of the energy required for the homolytic breakage of C-H, N-H and S-H bonds, (3) the effect of substituent groups on this latter, bond breaking process, and (4) organic reaction mechanisms involving the transfer of an electron. This work will provide insight into the pathway of organic reactions, especially those involving negatively charged species. The ease with which a molecule H-A can be cleaved thermally into two radical fragments, i.e., H-A giving H atom and A atom, provides an important insight into its reactivity. The Bordwell group has recently devised a method of estimating the size of such bond dissociation energies (BDE's) by combining the oxidation potential of the anion and the acidity constant of its conjugate acid, both measured in dimethyl sulfoxide solution. This method will be used to estimate BDE's for a large number of important weak acids for which BDE's have hitherto been inaccessible. By combining the oxidation potentials of the acid and the anion, and the acidity constant of the acid, the acidities of radical cations have been estimated. No previous information of this type has been available despite the importance of radical cations as intermediates. Finally, redox potentials combined with rate studies are expected to reveal significant new details concerning the role of single electron transfer in reactions of anions with electrophiles.
