Kinetic nitrogen isotope effects on methyl transfer to amines

Using 11C/14C Incoming Group and Secondary α-Deuterium KIEs To Determine How a Change in Leaving Group Alters the Structure of the Transition State of the SN2 Reactions between m-Chlorobenzyl para-Substituted Benzenesulfonates and Cyanide Ion

“…6 In fact, the only data that require a reactant-like transition state are the large k 11 /k 14 isotope effects. Although the authors are unable to explain why large k 11 /k 14 isotope effects are observed in this system where the best explanation of the data is a product-like transition state, it is important to note that all of the incoming group KIEs that have been reported [19][20][21][22][23][24][25] are normal or only very slightly inverse. In fact, the most inverse incoming group KIE was reported by Kurz et al, 21 who found a slightly inverse nitrogen incoming group KIE of 0.9937 ( 0.0002 for the Menshutkin reaction between 4-methylpyridine and methyl triflate in acetonitrile at 25 °C.…”

“…Although the authors are unable to explain why large k 11 /k 14 isotope effects are observed in this system where the best explanation of the data is a product-like transition state, it is important to note that all of the incoming group KIEs that have been reported [19][20][21][22][23][24][25] are normal or only very slightly inverse. In fact, the most inverse incoming group KIE was reported by Kurz et al, 21 who found a slightly inverse nitrogen incoming group KIE of 0.9937 ( 0.0002 for the Menshutkin reaction between 4-methylpyridine and methyl triflate in acetonitrile at 25 °C. The failure to find large inverse incoming group KIEs in the benzenesulfonate reactions suggests that the relationship between transition state geometry and the magnitude of the KIEs is not as simple as currently believed.…”

Using Incoming Group 11C/14C Kinetic Isotope Effects To Model the Transition States for the SN2 Reactions between Para-Substituted Benzyl Chlorides and Labeled Cyanide Ion

“…Kurz and co-workers also found very small nitrogen incoming group kinetic isotope effects in an extensive study of 25 S N 2 reactions between methyl and ethyl substrates and various amine nucleophiles. In spite of a wide variation in the leaving group, the nucleophile, and the solvent, the isotope effects are all very small, i.e., they were all between 1.0028 and 0.9937 with experimental errors ranging from 0.002 to 0.0002 . Finally, a small, but real, nitrogen kinetic isotope effect of 1.0019 ± 0.0001 in the Menshutkin reaction between methyl iodide and N,N -dimethyl- p -toluidine in methanol at 25 °C was reported by Paneth and O'Leary .…”

An Altered Mechanism of Hydrolysis for a Metal-Complexed Phosphate Diester

“…The magnitude of the 15 N KIE depends on the amount of negative charge developed on the leaving group in the transition state, while the 18 O lg KIE is a measure of P-O bond fission. 6 The data indicate much greater P-O bond fission and more negative charge on the leaving group in the transition state of the hydrolysis of diester complex 1 than in the hydrolysis of uncomplexed alkyl-pnitrophenyl phosphodiesters, consistent with the larger β lg .…”