Single electron transfer , versus

Fig. 19 Sn2 versus outer sphere, dissociative single electron transfer (in the case where this is adiabatic in all directions). (Adapted from Lexa et al 1988.)...

The oxidation of alkyl aryl sulfides to sulfoxides with oxochromium(V) complexes is first order in oxidant and in substrate. The better correlation of log k with a+ rather than a and the low magnitude of p+ value (-1.19) were interpreted as evidence for a rate-determining single-electron-transfer mechanism. This was further supported by good correlation in the plots of log k versus oxidation potential/ionization energy. 

M (CO)6 complexes all undergo irreversible electrochemical reduction in nonaqueous electrolytes at peak potentials close to —2.7 V versus SCE in tetrahydrofu-ran (THF) containing [NBu4][Bp4]. The product of the reductions are the din-uclear dianions [M2(CO)io] although under some conditions polynuclear products can also been obtained, Sch. 3 [2]. It was initially proposed that the primary step involved a single-electron transfer with fast CO loss and subsequent dimerization of the 17-electron radical anion [M(C0)5] [34]. A subsequent study showed that a common intermediate detected on the voltammetric timescale was the 18-electron species [M(CO)5] and that the overall one-electron process observed in preparative electrolysis arises by attack of the dianion on the parent material in the bulk solution, Sch. 2 [35]. 

This result contrasts with the observations on anthracene sensitized photolysis, wherein no arylated diarylsulfides are observed. Naphthalene cation radical is sufficiently oxidizing (naphthalene Eox = 1.54 V versus SCE) to oxidize diphenylsulfide ( ox = 1.31 V versus SCE), whereas anthracene cation radical cannot (anthracene Eox = 1.09 V versus SCE) [94], Thus, diphenylsulfide cation radical/phenyl radical pair is formed by two sequential single electron transfer reactions in-cage, the subsequent chemistry being the same... 

An investigation of why hydroxide makes the Tollens silver mirror test for aldehydes more sensitive has focused on thermodynamic versus kinetic factors. Electrochemistry tends to rule out the former the electromotive force (emf) of an appropriate cell changes little with pH. Exploring the kinetics, single electron transfer processes were confirmed by addition of a radical trap (TEMPO), which slowed the reaction. Rate measurements point to the rate of the formation of the anion of the gm-diol (i.e. the hydrate anion) as the key parameter affected by added hydroxide, a factor that also explains how the rapidity of the test varies with the structure of the aldehyde. 

Several kinds of information can be acquired from this experiment such as the total number of electrons transferred to the enzyme, the confirmation that a spectral intermediate is present along with its quantitation, and finally, an indication of whether the process occurs by two single electron transfers or a simultaneous two-electron transfer. A plot of absorbance at selected wavelengths versus number of electrons transferred can be used to analyze the data. Current efficiency is calculated by comparing the number of... 

SUBSTITUTION VERSUS SINGLE OUTER SPHERE DISSOCIATIVE ELECTRON TRANSFER... 

Becanse of the high concentration of isomeric molecules (>0.1 mol dm ), this equilibrium is established instantaneously. The IP of trans-AtcaYm is 0.02 eV lower than the IP of cw-decalin (9.24 eV versus 9.26 eV). Therefore, the electron-transfer eqnilibrinm is shifted slightly to the left side. Thns, in terms of charge-transfer kinetics, the two ions behave as a single species. It shonld be worth noting that decalin has only two isomeric forms, cis and trans. On the contrary, n-nonane exists in the multitude of conformations. The rate constant of electron exchange between parent nentral molecules of nonane and its cation-radicals is much lower, namely, 2 orders lower than the diffnsion-controlled limit (Borovkov et al. 2007). 

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