Cation kinetic analysis

Indeed, the (200-fs) laser excitation of the EDA complexes of various benz-pinacols with methyl viologen (MV2+) confirms the formation of all the transient species in equation (59). A careful kinetic analysis of the decay rates of pinacol cation radical and reduced methyl viologen leads to the conclusion that the ultrafast C—C bond cleavage (kc c = 1010 to 1011 s- ) of the various pinacol cation radicals competes effectively with the back electron transfer in the reactive ion pair. 

Furthermore, kinetic analysis of the decay rate of anthracene cation radical, together with quantum yield measurements, establishes that the ion-radical pair in equation (76) is the critical reactive intermediate in osmylation reaction. Subsequent rapid ion-pair collapse then leads to the osmium adduct with a rate constant k 109 s 1 in competition with back electron-transfer, i.e.,... 

Such competition between ion-pair collapse of MT+, C(N02)f and the radical-pair collapse of MT+, NO is also readily modulated by the addition of inert salt.14 The description of the solvent and salt effects in equations (82) and (83) is further confirmed by direct kinetics analysis of the decay of the cation radical MT+ on the nanosecond/microsecond timescale. 

Chenevier, P., Veyret, B., Roux, D. and Henry-Touleme, N. (2000). Interaction of cationic colloids at the surface of J774 cells a kinetic analysis, Biophys. J., 79, 1298-1309. 

Adam et al. (2003) also explained their experimental results on the rearrangement of housanes through mechanisms that include the formation of distonic cation-radicals in the intermediary step. Their mechanisms were grounded by kinetic analysis (Trofimov 2004). 

Santry and McClelland (1983a) also generated the tetrahedral intermediate of an 0,S-acyl transfer reaction from an orthothiolester precursor [83]. At PH < 3 the cation [84] could be detected by its strong absorption at X = 350 nm and it was concluded from a kinetic analysis that this was in equilibrium with the hemiorthothiolester [85]. 

Electron transfer may also dominate the excited state chemistry of open shell radical ions. The fluorescence of the radical anions of anthraquinone and 9,10-dicyanoanthracene and the radical cation of thianthrene are quenched by electron acceptors and donors, respectively, although detailed kinetic analysis of the electron exchange do not correspond exactly either with Weller or Marcus theory (258). The use of excited radical cations as effective electron acceptors represents a... 

A review has focused on differentiation between polar and SET mechanisms through kinetic analysis.82 hi two separate reviews, the effects of solute-solvent interactions on electron-transfer reactions have been described.83,84 A review of the behaviour of radical cations in liquid hydrocarbons has given particular emphasis to those with high mobility.85 A paper presents selected studies in the formation of radicals by oxidation with manganese- or cerium-based reagents and then- application to C—C bond formation by SET processes.86... 

Reaction (76) has been believed to ruled out in a kinetic analysis of the Fenton reaction by EPR spin trapping (Mizuta et al. 1997) [a caveat is the observation that in water spin traps may be oxidized to the OH-adduct via the spin trap radical cation by strong oxidants (Eberson and Persson 1997 von Sonntag et al. 2004)], but reaction (77), already suggested earlier (Rush and Koppenol 1987), was required to account for their data. 

Nakano, A. Xie, Q. Mallen, J. V. Echegoyen, L. Gokel, G. W., (1990) Synthesis of a membrane-insertable, sodium cation conducting channel kinetic analysis by dynamic sodium-23 NMR J. Am. Chem. Soc. 112, 1287-1289. 

Atomic absorption spectrophotometric analysis and kinetic analysis of wild-type 1,2-a-D-mannosidase were performed. Concentrations of Ca2+ were determined by atomic absorption spectrophotometric analysis. The purified recombinant wild type 1,2-a-D-mannosidase almost completely did not contain Ca2+. Other divalent metal cations including Mg2+, Mn2+, Co2+, Cu2+, and Zn2+ were also not detected. 

The kinetic analysis of the El elimination of Figure 4.32 must be conducted for both options A and B for the further reaction of the tert-butyl cation ... 

Kinetic analysis of this system enables the data of Table 20 to be derived. The ratios k 3/k2 give a measure of the relative catalytic effectiveness of the cations since k2 is independent of the electrophile. The resulting order, Li+ > K+ > n-Bu4N+, is similar to that reported for the electrophile-assisted ionizations of p-methoxy-neophyl tosylate and the p-nitrobenzoate of spiro- [4,5 ] -deca-6,9-dien-8-ol in acetone (Winstein et al., 1964). The absence of these effects with the chloro compound is in accord with the observations that aromatic chloro derivatives are not usually subject to electrophilic catalysis of leaving group departure (Bemasconi, 1973). 

For ion-pair extraction, a cation is extracted with an anion into oil. In this case, individual ions or the ion pair species transfer across a microdroplet/water interface and the extraction rate is expected to depend on the Galvani potential between the microdroplet and water, the ion transfer potentials across the liquid/liquid interface, the association constant of the ions in the solution and so forth [46-54]. Therefore, the mass transfer processes are complicated even in the absence of adsorption of an ion at the microdroplet/water interface. In this section, the kinetic analysis of a simple ion-pair extraction without adsorption is described and the extraction mechanism is discussed on the basis of the single microdroplet technique. 

Ion-pair extraction of an anionic surfactant with a cationic dye such as methylene blue from water into oil is often used for the quantitative analysis of the surfactant in water [57,58]. The surfactant concentration in water is then determined as the dye concentration in the oil or water phase by conventional absorption spectroscopy. Synthetic surfactants such as sulfates and sulfonates completely dissociate in water even at low pH. On the other hand, the association of fatty acid salts (traditional soaps) with H" " depends on the pH. Therefore, the quantitative analysis of surfactants in water is performed by the ion-pair extraction at various pHs. Although quantitative analysis and thermodynamic studies have been already reported for the anionic surfactant/cationic dye extraction, kinetic analysis of the ion-pair extraction has been rarely reported and the extraction mechanism is not discussed in detail. In this section, we describe the kinetic analysis of the extraction of a dodecyl sulfate anion with methylene blue as a typical example using the single microdroplet manipulation and microabsorption methods [59]. In particular, the pH dependence of the ion-pair extraction is discussed. 

Kinetic analysis of the coupling of 4-methoxybiphenyl radical cation"... 

Pistoia investigated the electroinitiated polymerisation of styrene in propylene carbonate-lithium perchlorate solutions at 25°C. Mechanistic evidence was obtained for the formation of perchloric acid at the anode and the cationic nature of the process thus proved. The kinetic analysis yielded a kp value of 0.5 M sec . Although no comparisons can be made between this result and previous ones in other solvents, the presence of lithium perchlorate was here a source of homocorgugation for the acid produced and thus the cause of considerable deactivation of its initiating power. As in previous cases, this was not recognised by the author. A simflar study by Pistoia and Scro-sati in dimethylsulphate gave an insoluble polymer at the anode and the nature or the initiator was not elucidated, but it did not seem to be perchloric acid. The cationic properties of this process was however proved... 

A limited number of attempts have been made to set up a general mechanistic scheme describing cationic systems in terms of fundamental reactions, in a similar manner to that used in free radical polymerizations, and to derive generally applicable kinetic equations [3—4]. Because of the individuality of each cationic system, however, this approach has met with little success, and there has been a greater tendency towards treating each polymerization in isolation for detailed kinetic analysis. It is possible, however, to postulate at least token schemes which can be used as a guide. After the pre-initiation equilibria, polymerization can be considered in terms of classical initiation, propagation, transfer and termination reactions, i.e. for vinyl monomers... 

There have been some extensive studies of the cationic polymerization of EO [1] and of epichlorohydrin (ECH) [26]. Neither of these efforts has resulted in a clear kinetic picture. The reason seems to be that a very complex series of reactions occurs and a sensible kinetic analysis just has not emerged. 

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