Dissociation rate constants and partitioning ratios for reactions

Table 1. Dissociation rate constants and partitioning ratios for reactions of various 6i5(pyridine)-halonium ions with acceptor olefins in CICH2CH2CI,...

Using the various simplifications above, we have arrived at a model for reaction 11.9 in which only one step, the chemical conversion occurring at the active site of the enzyme characterized by the rate constant k3, exhibits the kinetic isotope effect Hk3. From Equations 11.29 and 11.30, however, it is apparent that the observed isotope effects, HV and H(V/K), are not directly equal to this kinetic isotope effect, Hk3, which is called the intrinsic kinetic isotope effect. The complexity of the reaction may cause part or all of Hk3 to be masked by an amount depending on the ratios k3/ks and k3/k2. The first ratio, k3/k3, compares the intrinsic rate to the rate of product dissociation, and is called the ratio of catalysis, r(=k3/ks). The second, k3/k2, compares the intrinsic rate to the rate of the substrate dissociation and is called forward commitment to catalysis, Cf(=k3/k2), or in short, commitment. The term partitioning factor is sometimes used in the literature for this ratio of rate constants. 

The equations used in our study of the thermodynamics and kinetics of thermal electron reactions using the ECD and NIMS are presented. The ECD and NIMS methods were developed in our laboratories. These are used to determine the rate constants, electron affinities, partition function ratios, and bond dissociation energies of molecules and energies for the formation of complexes of anions. The general kinetic model for the ECD and negative-ion mass spectrometry is presented. Molecules will be classified using example data. 

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