Nitrogen isotopic exchange

The kinetics of reaction (29) have been investigated by rapid-scan i.r. spectroscopy. The experimental rate constant is in reasonable agreement with an earlier calorimetric value, but the use of isotopic NO has now established the reaction mechanism to be a Cl atom transfer. Rate constants for the nitrogen isotope exchange reactions (30) and (31) have also been determined. ... 

The rate of nitrogen isotope exchange corresponds to the forward and backward rate of the first step. If the rate determining step is the first step, the rate of isotope exchange (reverse reaction) should be zero at ammonia synthesis conditions. This method can be used for the determination of reaction rate determining step for Ru-K/AC(Ref. 172) and Mo2N. ... 

N2 isotopic exchange over fused Fe is inhibited by O2 [490]. The activation energy for nitrogen isotope exchange is higher in the presence of chemisorbed oxygen [534]. 

Addition of a small amount of K results in an increase in the catalytic activity for ammonia synthesis [139, 217, 240, 242, 244, 248, 249, 288, 289, 609-611] and an increase in activity for nitrogen isotopic exchange [611]. For ammonia synthesis the acitivity effect depends on the pressure [563, 564]. 

The H/D isotopic exchange in the uridine system (from starred nitrogen) may be explained by the mechanism (equation 8) involving dimerization of the hydroxy heterocycle70. Dimerization of hydroxy derivatives of aza-containing heterocycles plays an important role in assembling molecules, and in their tautomeric equilibria. 

Kirkley MB, Gurney JJ, Otter ML, HiU SJ, Daniels LR (1991) The application of C-isotope measurements to the identification of the sources of C in diamonds. Appl Geochem 6 477 94 Kirshenbaum I, Smith JS, Crowell T, Graff J, McKee R (1947) Separation of the nitrogen isotopes by the exchange reaction between ammonia and solutions of ammonium nitrate. J Chem Phys 15 44(M46... 

Firestone, M. K., Firestone, R. B., and Tiedje, ]. M. (1979). Nitric oxide as an intermediate in denitrification Evidence from nitrogen-13 isotope exchange. Biochem. Biophys. Res. Commun. 91, 10-16. 

Shearer, G., and Kohl, D. H. (1988). Nitrogen isotope fractionation and "O exchange in relation to the mechanism of denitrification of nitrite by Pseudomonas stutzeri. J. Biol. Chem. 263, 13231-13245. 

One of the important features of D20 is its ability to undergo isotope exchange with many compounds. For example, when NH3 is placed in D20, all of the H atoms exchange rapidly with deuterium. Presumably, this is because the exchange with NH3 can proceed by interaction of D20 with the unshared pair of electrons on the nitrogen atom in an associative process that can be illustrated as... 

The area is an important surface parameter for catalytic studies. It is needed to evaluate the rate constant of the surface reaction from the kinetics as well as to allow a fair comparison to be made of the effectiveness of different catalysts. Areas are commonly determined by nitrogen or krypton gas adsorption interpreted by the Brunauer-Emmett Teller (BET) isotherm [30, 32], A number of other methods has been proposed and utilised including microscopy, isotopic exchange, chromatography, gas permeability, adsorption from solution, and negative adsorption (desorption) of co-ions [30, 33]. 

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