With support from the Organic Dynamics Program of the Chemistry Division of NSF, Professor Kenneth R. Fountain of Northeast Missouri State University will study the alpha effect, i.e. the rate enhancement in nucleophilic substitution reactions deriving from the presence of a second lone pair of electrons adjacent to the attacking pair on the nucleophile. The project lies within the NSF Program for Research in Undergraduate Institutions. The issue to be examined is the extent to which single electron transfer (SET) models the reactivity in such reactions. Rates of transfer of alkyl groups from alkyldiarylsulfonium salts to alpha or non-alpha nucleophiles will be measured. Since the sulfonium salts are amenable to electrochemical analysis, structure-reactivity studies affording plots of log(rate) vs. redox potential can be constructed and the effect of SET capability deduced therefrom. Computations at the 3-21G** level, kinetic isotope effect studies, and certain studies of symmetric substitutions expected to lead to radical trapping, will also contribute to the project. Study of nucleophilic substitutions, reactions well known to undergraduate students of organic chemistry, will provide understanding of an effect of a certain structural change of the nucleophile on reactivity. The experimental work will be supported by computational modeling. The project design encourages students to view their individual work in the context of a larger and overarching scientific goal.
