Proton-assisted electron transfer mechanism

This process can be contrasted directly with the oxo transfer scheme (Reaction 16) discussed above. In either case, the cleavage of the N-O bond is assisted by the binding of oxygen to an electrophile (to molybdenum itself in the oxo transfer mechanism or to proton(s) in the coupled proton-electron transfer scheme). Although the coupled proton-electron transfer mechanism would possibly have the advantage of leaving an open site on molybdenum to restart the cycle, there is no strong data to support either of these mechanisms at present. 

With the aim of clarifying the processes involved in stages I and II an idealised representation of a proposed reaction between water and a strained ceramic bond at the crack tip has been proposed [7,16]. Reaction steps involve (1) adsorption of water to ceramic bond, (2) reaction involving simultaneous proton and electron transfer, and (3) formation of surface hydroxyls. The susceptibility of a given ceramic to the mechanism of stress assisted corrosion by water, hence to SCG, lies in its ability to react with water and to dissociate. Glass was studied in the past as a model ionic material with a high susceptibility to SCG, because stressed Si-O-Si bounds... 

There has been nothing like the enthusiasm for the application to these systems of the theoretical equations, which we have noted in the previous sections and will encounter in the next. Nevertheless, a number of features are present which are qualitatively consistent with the discussions in Sec. 5.8.1 and which are in part illustrated in Table 5.11. There is a correlation of rate constant with the driving force of the internal electron transfer. -pjjg p. itro-phenyl derivative is a poorer reducing agent when protonated and k is much less than for the unprotonated derivative. Consequently disproportionation (2A 3) becomes important. Although there are not marked effects of structural variation on the values of A , the associated activation parameters may differ enormously and this is ascribed to the operation of different mechanisms."" The resonance-assisted through-chain operates with the p-... 

The toluene-soluble fraction consists of a major product that has been identified as a CgQ-TEA monocycloadduct 7V-ethyl-rra/w-2, 5 -dimethyl-pyrrol-idino[3, 4 l,2][60]fullerene (14) by use of matrix-assisted laser desorption ionization mass spectroscopy and NMR methods [71]. It is interesting that the photochemical reaction actually results in the formation of a cycloadduct. This is unique to the fuilerene system because there have been no reports of cycloadducts in reactions involving nonfullerene acceptors [119-122], such as rra/is-stilbene. In the context of the classical photoinduced electron transfer-proton transfer mechanism [124], a two-step process for the formation of the cycloadduct has been proposed [71]. 

Our data give k. 5.4 M" sec" for tert-hutyl hydroperoxide, and kjj/k]) 2.8 for tert-BuOOD at -4 . This primary isotope effect establishes the mechanism of eq 35 as an assisted scission of an 0-H bond, rather than a rate limiting electron transfer followed by a rapid proton transfer, eqs 35a,b. In addition, the heat of... 

In an APCI interface the column effluent enters a heated nebulizer where the pneumatically assisted desolvation process is almost completed. While still in the spray chamber, ionization of analytes is initiated by corona discharge. The ionization mechanisms in APCI are almost identical to those in conventional medium pressure chemical ionization (7). Positive ion formation can be achieved by proton transfer, adduct formation or charge exchange reactions, while in the negative mode ions are formed due to proton abstraction, anion attachment and electron capture reactions. The APCI interface is compatible with flow rates exceeding 1 ml/min and will... 

A new mechanism by which poly(aniline) conducts electricity has been established by J. P. Travers and M. Nechtschein. The conduction process can be accounted for in terms of electrons hopping between localized states under the assistance of proton transfer, for which the presence of water plays an essential role [107] (Figure 12). 

Overall, these early studies of carboxylate-assisted intramolecular C-H activation established the key features of these AML A/CMD processes, where an electron-deficient metal center works in concert with a pendant carboxylate base to promote C-H activation. This is most evident when an agostic intermediate is involved and such species also rationalize how these systems can also perform C(sp )-H bond activation. Whether C-H activation is achieved as a one- or two-step process appears rather system dependent. Alternative mechanisms, for example, proton transfer onto a halide ligand, oxidative addition, or AMLA-4 processes involving proton transfer onto the inner (Pd-bound) oxygen of the carboxylate were all ruled out. Likewise, no evidence for S Ar processes had been reported. Subsequent work was set against this background and considered the various other parameters that may affect the C-H bond activation process. 

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