Rate constant interchange reaction

Based on this description, the rate constant for reaction (3) would reflect the onset of two coupled initial equihbria (Kec, K )), followed by the irreversible ligand-interchange reaction, i.e., = x X fe H20- From an... 

Data for the reaction of nitrous acid with hydrogen peroxide1 follow Eq. (4-22), with kf = 3.76 s"1 and ks = 0.0854 s"1. We now show that either kf or ks may be k or k2. That is, an absorbance reading that rapidly rises and slowly declines does not necessarily imply the first step is fast and the second slow. Inspection of the expression for [P]f, Eq. (4-8), and that for Yt, Eq. (4-18), shows their symmetry upon interchange of A i and k2. Absent other information, the two rate constants cannot be assigned. 

Reactions of D with D20 and of 0 with 02, N20, and N02 have been studied with a magnetic sector mass spectrometer. Competition between electron transfer and ion-atom interchange has been observed in the production of 02 by reaction of 0 with 02, an endothermic reaction. The negative ion of the reacting neutral molecule is formed in 02, N2Of and N02 but not in D20. Rate constants have been estimated as a function of repeller potential. 

Realizing that the last four reactions of the ion-atom interchange mechanism listed each have only one-half the statistical probability of occurring as do the first four and assuming no isotope effect on the rate constants, we can write the following set of rate equations ... 

Kinetics and activation parameters for NO reactions with a series of iron(II) aminocarboxylato complexes have been obtained (Table II) in aqueous solution (31). Rate constants for these reactions ranged from 105 to 108M-1s-1 for the series of iron(II) complexes studied. The reactions of NO with Fen(edta) (edta = ethylenediaminetetraacetate) and Fen(Hedtra) (Hedtra = hydroxyethylenediaminetriacetate) yielded activation volumes of +4.1 and +2.8 cm3 mol-1, respectively and were assigned to a dissociative interchange (Id) mechanism (31b). All of the iron(II) aminocarboxylato complexes studied followed a similar pattern with the exception of the Fen(nta) (Nta = nitriloacetic acid) complex which gave a AV value of —1.5 cm3 mol-1. The reaction of this complex with... 

The rate constants and k represent rate constants for a surface reaction and have units m mol s and s respectively. The accelerative effects are about 10 -10 fold. They indicate that both reactants are bound at the surface layer of the micelle (surfactant-water interface) and the enhanced rates are caused by enhanced reactant concentration here and there are no other significant effects. Similar behavior is observed in an inverse micelle, where the water phase is now dispersed as micro-droplets in the organic phase. With this arrangement, it is possible to study anion interchange in the tetrahedral complexes C0CI4 or CoCl2(SCN)2 by temperature-jump. A dissociative mechanism is favored, but the interpretation is complicated by uncertainty in the nature of the species present in the water-surfactant boundary, a general problem in this medium. 

When an associative mode of activation is indicated it is instructive to examine the ways in which reactivity, as measured by the second-order rate constant k2, depends upon the nature of the nucleophile and if a large number of substrates show the same pattern of preference it is useful to consider scales of nucleophilicity. A systematic study of the substitution reactions of fra/is-[Pt(py)2Cl2] (it appears that pyridine and piperidine were used interchangeably) in methanol at 30 °C (displacement of chloride) led to the establishment of an n scale, nm d= log,o(k2/kI) for the standard reaction,447 and later the more dimensionally correct Up,0 scale448-449 ( p,° = log,0(li2/ki)[MeOH]) so that npt° = npt+1-41 (unfortunately this distinction has not been strictly adhered to in the literature).449 A collection of n 0 values will be found in Table 14. 

The rate constants are so defined that a constant has fys+ixa-n as the rate constant for the reverse reaction. This means that the rate constants for the fore and back reactions must lie at an equal distance taken symmetrically from either side of the all-zero off-diagonal of the matrix. From inspection of the matrix, it can be seen that there are v(v— 1) different rate constants for second-order interchanges leading to chemically different molecules. 

Szajewski RP, Whitesides GM (1980) Rate constants and equilibrium constants for thiol-disulfide interchange reactions involving oxidized glutathione. J Am Chem Soc 102 2011-2026... 

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