Bimolecular electron-transfer processes

Flash Photolysis Studies in Bimolecular Electron-transfer Processes... 

Femtosecond time-resolved studies on bimolecular electron transfer processes... 

Bimolecular Electron Transfer Processes of Nucleosides, Nucleotides, and Oligonucleotides... 

Femtosecond times-resolved studies on bimolecular electron transfer processes S. Pages, B. Lang and E. Vauthey... 

Much of the kinetic work has been concerned with the oxidation of isopropyl alcohol to acetone in aqueous sulphuric or acetic acids. The rate-determining step definitely involves the breaking of a carbon-hydrogen bond, as isopropyl alcohol is oxidised 6-7 times faster than its 2-deutero derivative . At all acidities, the rate of oxidation shows a first-order dependence on both the concentration of HCr04 and the alcohol, but the dejiendence on [H] varies. In dilute acidic solution the rate is proportional to [H] , to [H] in more concentrated solution and to Ho in 20-60% aqueous sulphuric acid . These observations are consistent with two mechanisms (i) a bimolecular electron transfer process (218) ,... 

Scheme 13 no longer fits the S l acronym since the process in which the bond to the leaving group is broken is a dissociative bimolecular electron transfer process. Another type of Srn2 process is described in Scheme 15. 

The study of the dynamics of spin-state changes is important for the understanding of the kinetics of bimolecular electron transfer reactions ° and racemization and isomerization processes (Sec. 7.5.1). Low spin — high spin equilibria, often attended by changes in coordination numbers, are observed in some porphyrins and heme proteins, although their biological significance is, as yet, uncertain. 

Steric constraints dictate that reactions of organohalides catalysed by square planar nickel complexes cannot involve a cw-dialkyl or diaryl Ni(iii) intermediate. The mechanistic aspects of these reactions have been studied using a macrocyclic tetraaza-ligand [209] while quantitative studies on primary alkyl halides used Ni(n)(salen) as catalyst source [210]. One-electron reduction affords Ni(l)(salen) which is involved in the catalytic cycle. Nickel(l) interacts with alkyl halides by an outer sphere single electron transfer process to give alkyl radicals and Ni(ii). The radicals take part in bimolecular reactions of dimerization and disproportionation, react with added species or react with Ni(t) to form the alkylnickel(n)(salen). Alkanes are also fonned by protolysis of the alkylNi(ii). 

Bimolecular excited state electron transfer reactions have been investigated extensively during the last decade (1-3). Electron transfer is favored thermodynamically when the excitation energy E of an initially excited molecule A exceeds the potential difference of the redox couples involved in the electron transfer process. 

The discussion so far has been in relation to bimolecular electrophilic oxidation by hydrogen peroxide via a two-electron donor substrate. However, the oxidation process can also be envisaged as a single electron transfer process (SET). The two mechanisms are not that dissimilar152 and can be viewed as two sides of the same coin. The bimolecular mechanism can be visualized as an... 

In recent years, much work has been done on the electron transfer phenomenon called free electron transfer (FET). FET stands for an electron transfer process where the molecule oscillations of the donor are reflected in a bimolecular reaction. This is reasoned by an unhindered electron jump proceeding in the first encounter of the reactants. So free means unhindered and concerns the transfer, not the electron. 

One of the available ways for investigating intramolecular electron transfer is that of inducing a charge shift by bimolecular PET (Figure Ic). The feasibility of this relies on the fact that the bimolecular event producing the thermodynamically unfavored electronic isomer of the dyad is faster than the intramolecular electron transfer process to be observed. When this requirement is met, since the back recombination reaction is a bimolecular process, relatively slow intramolecular electron transfer processes can be studied. This type of process has been extensively used for studying electron transfer in proteins [206], but has not been frequently applied to dyads. In an early study [207], the Rh(III)-diquat dyad (28) was... 

Flash irradiation with visible light (2 > 400 nm) of a thermally equilibrated solution gives rise to an instantaneous increase of the I3 concentration, followed by a slow decrease in the dark. Although the extremely short lifetime of the [Fe(CN)6] excited state prevents any type of bimolecular process, a photoinduced electron transfer process is responsible for the increased I3 concentration upon irradiation. The positively charged supercomplex forms an ion pair with the iodide anion, so that a very fast electron transfer process can take place following a imimolecular kinetics. 

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