NSERC grants at Laurentian University Subventions du CRSNG `a l ...

68Kenneth WestawayUsing kinetic isotope effects to model the SN2 transitionstateA grant of $45,000 per year.Une subvention de 45 000 $ par année.Discovery Grant – Subvention à la découverteReplacing an atom in a chemical reaction with itsisotope often causes a change in the rate of a reaction.The change in rate caused by the isotope is called akinetic isotope effect (KIE). We have spent considerableeffort learning how to interpret secondary alphadeuterium(where a hydrogen at the reacting carbonatom is replaced by deuterium) KIEs and to relate themagnitude of these KIEs to the structure of the transitionstate (the high energy species that forms duringthe reaction) of substitution reactions.Nu- + RCH2-X → RCH2-Nu + XWe will use heavy atom (carbon, nitrogen or chlorine) and primary andsecondary deuterium KIEs to determine the structure of the transition statesof several substitution reactions to learn how and why changes in1. the structure of the reactants (substitutent effects);2. the solvent, i.e. the reaction medium;3. ion-pairing of the nucleophile (Nu-); and4. increasing the ionic strength of the reaction medium by adding inert saltsto the solvent,affect substitution reactions and their transition states.The proposed research will1. develop new kinds of KIEs that can be used by ourselves and others todetermine transition state structure; and