Deuterium transfer, competition

Analysis of the pH-dependence of the kinetic parameters and competitive inhibitor K values indicates that the p/fa values of the Bi and B2 groups are 7.6 and 6.0, respectively.791 These groups have not been identified, but the observed low degree of deuterium transfer ( 8%)80 82) suggests that the basic group Bi is polyprotic and, therefore, may be the -amino group of a lysine residue. 

The exo and the endo ring closures (the kc reactions) are in competition with the aryl radical-tributyltin hydride transfer (the ks or ku reaction). These workers162 used this competition to determine the primary hydrogen-deuterium kinetic isotope effect in the hydride transfer reaction between the aryl radical and tributyltin hydride and deuteride. 

The strategy above provides a means to understand the competition between H-atom transfer and electron transfer + protonation in general. Additionally, it may be used to gather values for H-atom abstraction rate constants and kinetic isotope effects that are not readily accessible otherwise. It also provides guidelines for optimizing deuterium incorporation reactions. 

Probing mechanism of the reaction involving intramolecular competition between different isotopic species at several chemically equivalent positions, the number of equivalent sites must be taken into consideration. In the case of deuterium content at natural abundance the concentration of multiply labelled molecule is negligible and not-deuterated molecules are invisible in the 2H NMR. When reaction is taken to the completion the retained and transferred deuterium can be calculated from the 2H spectra of substrate and product. The KIE is given by ... 

---