Kinetic corroborated

Kochi (1956a, 1956b) and Dickerman et al. (1958, 1959) studied the kinetics of the Meerwein reaction of arenediazonium salts with acrylonitrile, styrene, and other alkenes, based on initial studies on the Sandmeyer reaction. The reactions were found to be first-order in diazonium ion and in cuprous ion. The relative rates of the addition to four alkenes (acrylonitrile, styrene, methyl acrylate, and methyl methacrylate) vary by a factor of only 1.55 (Dickerman et al., 1959). This result indicates that the aryl radical has a low selectivity. The kinetic data are consistent with the mechanism of Schemes 10-52 to 10-56, 10-58 and 10-59. This mechanism was strongly corroborated by Galli s work on the Sandmeyer reaction more than twenty years later (1981-89). 

Perhaps the most extensive computational study of the kinetics of NO reactions on Rh and Pd surfaces has been provided by the group of Zgrablich. Their initial simulations of the NO + CO reaction on Rh(lll) corroborated the fact that the formation of N-NO intermediate is necessary for molecular nitrogen production [83], They also concluded that an Eley-Rideal mechanism is necessary to sustain a steady-state catalytic regime. Further simulations based on a lattice-gas model tested the role of the formation of... 

This reaction is very exothermic (A// —180 to —200kJ mol-1) and, therefore, seems to be very probable from the thermochemical point of estimation. The pre-exponential factor is expected to be low due to the concentration of the energy on three bonds at the moment of TS formation (see Chapter 3). To demonstrate that this reaction is responsible for the oxidative destruction of polymers, PP and PE were oxidized in chlorobenzene with an initiator and analyzed for the rates of oxidation, destruction (viscosimetrically), and double bond formation (by the reaction with ozone) [131]. It was found that (i) polymer degradation and formation of double bonds occur concurrently with oxidation (ii) the rates of all three processes are proportional to v 1/2, (iii) independent of p02, and (iv) vs = vdbf in PE and vs = 1.6vdbf in PP (vdbf is the rate of double bond formation). Thus, the rates of destruction and formation of double bonds, as well as the kinetic parameters of these reactions, are close, which corroborates with the proposed mechanism of polymer destruction. Therefore, the rate of peroxyl macromolecules degradation obeys the kinetic equation ... 

The kinetics and mechanism of ligand substitution reactions of square-planar platinum(II) dimethyl sulfoxide complexes have been exhaustively studied (173), and these workers conclude that the cis and trans influences and the trans effects of Me2SO and ethylene are similar in magnitude whereas the cis effect of Me2SO is about 100 times as large as that of ethylene. The results for reaction (5), where the stability constants, Kt, are reported to be 1.5 x 108 (L = S-Me2SO) and 4.5 x 108 (L = ethylene) corroborate this analogy (213). 

Equation (4) corresponds to saturation-type (Michaelis-Menten) kinetics and rate constants obtained over a suitable range of [CD], sufficient to reflect the hyperbolic curvature, can be analysed to provide the limiting rate constant, kc, and the dissociation constant, Ks (VanEtten et al., 1967a Bender and Komiyama, 1978 Szejtli, 1982 Sirlin, 1984 Tee and Takasaki, 1985). The rate constant ku is normally determined directly (at zero [CD]), and sometimes Ks can be corroborated by other means (Connors, 1987). 

Table I shows the various Mossbauer nuclides—i.e., the nuclides where the Mossbauer eflFect has actually been seen. Not all of these are as easy to exploit as the Fe and 9Sn cases referred to above. However, with improved techniques a number of these should prove accessible to the chemist. Representative elements of almost all parts of the periodic table are tractable by these techniques. It seems clear, however, that the methods of Mossbauer spectroscopy are no longer technique-oriented but that this field is becoming a problem-oriented discipline. In other words, the Mossbauer effect is now used successfully in many cases not only to demonstrate the effect or to corroborate physical evidence obtained by other means—NMR, or infrared, or kinetic studies— but also to solve new chemical problems.

Until recently, the most detailed kinetic investigations of phase transfer free radical polymerizations were those of Jayakrishnan and Shah (11, 12). Both of these studies have been conducted in two phase aqueous/organic solvent mixtures with either potassium or ammonium persulfate as the initiator, and have corroborated our earlier conclusions (2, 3)... 

Attention. In pursuing high ee of the digested products (more reactive enantiomers) under kinetically resolving conditions, termination of the reaction at the proper conversion is very important. When the relationship between conversion and ees of the digested product and of the unaffected substrate was calculated using the mathematical model of Chen et al., it was predicted that 80 % conversion should be the critical point, as depicted in Figure 5.3, which corroborated the empirical results mentioned in steps 2 and 3. 

The broad and nearly universal applicability of the cinchonan carbamate CSPs for chiral acid separations is further corroborated by successful enantiomer separations of acidic solutes having axial and planar chirality, respectively. For example, Tobler et al. [124] could separate the enantiomers of atropisomeric axially chiral 2 -dodecyloxy-6-nitrobiphenyl-2-carboxylic acid on an C-9-(tert-butylcarbamoyl)quinine-based CSP in the PO mode with a-value of 1.8 and Rs of 9.1. This compound is stereolabile and hence at elevated temperatures the two enantiomers were interconverted during the separation process on-column revealing characteristic plateau regions between the separated enantiomer peaks. A stopped-flow method was utilized to determine the kinetic rate constants and apparent rotational energy barriers for the interconversion process in the presence of the CSP. Apparent activation energies (i.e., energy barriers for interconversion) were found to be 93.0 and 94.6 kJ mol for the (-)- and (-l-)-enantiomers, respectively. 

As discussed in section 6.1, a relatively exhaustive HRTEM and AFM study was conducted by Mitter-dorfer and Gauckler of how secondary phases form at the LSM/YSZ boundary and how these phases effect electrode kinetics. This study placed the time scale for cation-transport processes in the correct range to be consistent with the theory described above. However, while all this may be interesting and useful speculation, to date no in-depth studies of the LSM surface as a function of A/B ratio, polarization history, or other factors have been performed which would corroborate any of these hypotheses. Such a study would require combining detailed materials characterization with careful electrochemical measurements on well-defined model systems. Given the... 

The selectivity factors determined in potentiometric studies (K[,ot) should therefore be identical to the ones (Kjj) determined in transport experiments. In Fig. 4 selectivities obtained potentiometrically on a membrane containing ligand 11 (3 wt.% carrier 11, 65 wt.% dibutyl sebacate 32 wt.% polyvinyl chloride, thickness =100 /xm) are compared with those obtained in electrodialytic transport experiments.55 Although widely different methods have been used to determine the ion selectivity, the agreement between the two sets of data is evident and corroborates the model presented. The deviation for CsH may possibly be due to kinetic limitations suggesting a loss in transport selectivity (see Section IV.D). 

This last explanation appears to be the most feasible since we did not observe deviations from the expected half-order kinetic law when those multiacrylate monomers were polymerized in dilute solution where no rigid network is formed (30). A further feature which corroborates this conclusion is... 

This result has been corroborated by numerous other examples43,593,597,601,608-614 and fits well with the classical mechanism described in Scheme 2. Only a few examples of second-order reactions are known they concern in particular the alkaline hydrolysis of phosphonium salts 29s 86,615 and 30616. In both cases, the second-order kinetics are very likely the result of a direct substitution induced by the very high stability of the carbanion resulting from the P—C bond cleavage. 

Investigation of the influence of the solvent on the kinetics of the reaction corroborate, in the same way as the order of the reaction, the formation of hydroxyphosphorane. Kinetic investigations have been performed with various solvent mixtures EtOH-H2Q601.608,616-620 Me0H-H20610,61 Me0CH2CH20Me-H20583 586,595,621,... 

As we discussed in Chapter 3, the KM for an enzymatic reaction is not always equal to the dissociation constant of the enzyme-substrate complex, but may be lower or higher depending on whether or not intermediates accumulate or Briggs-Haldane kinetics hold. Enzyme-substrate dissociation constants cannot be derived from steady state kinetics unless mechanistic assumptions are made or there is corroborative evidence. Pre-steady state kinetics are more powerful, since the chemical steps may often be separated from those for binding. 

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