THE C-11/C-14 KINETIC ISOTOPE EFFECT METHOD - THE C-11/C-14 KINETIC ISOTOPE EFFECT IN THE SN2 REACTION OF N,N-DIMETHYL-PARA-TOLUIDINE WITH LABELED METHYL-IODIDE

Methodological aspects of the determination of C-11/C-14 kinetic isotope effects (KIEs) were investigated using the reaction of N,N-dimethyl-p-toluidine with labelled methyl iodide in methanol at 30-degrees-C as model system. The primary C-11 KIE was determined to be 1.202 +/- 0.008 for this reaction. The isotope effect was determined by a one-pot technique based on liquid chromatographic fractionation of the reactant and product followed by liquid scintillation counting of the C-11 and C-14 radioactivity in these fractions. The KIE value obtained agrees well with the value predicted from a previously determined C-12/C-14 KIE for the same reaction. Theoretical model calculations of both carbon KIEs were performed using the BEBOVIB IV program. Transition-state models ranging from reactant- to product-like were employed in the calculations, and three different reaction coordinate models with more or less pronounced Walden inversion of the methyl hydrogens were investigated.