Single electron transfer step

The mechanism includes two single electron transfers (steps 1 and 3) and two proton transfers (steps 2 and 4) Experimental evidence indicates that step 2 is rate determining and it is believed that the observed trans stereochemistry reflects the dis tribution of the two stereoisomeric alkenyl radical intermediates formed in this step... 

In any fast multielectron transfer reaction all the electrons cannot be transferred in one step but only by a succession of single-electron transfer steps, whereas Eq. (6) was arrived at by Devanathan31 for the simple case in which it is assumed that the same step is rate determining in both directions, irrespective of the number of electrons involved in the reaction. 

Leaving aside very simple inorganic single electron transfer steps, such as those discussed above, the simplest mechanism conceivable would consist of two processes, one chemical and the other electrochemical, denoted CE or EC. A simple example of a CE process would be the reduction of a weak acid, such as acetic acid ... 

The oxidation of 3,6-dehydrohomoadamantane (52) with NO+BF4, photo-excited tetracyanobenzene, and under anodic conditions has been found to involve a common radical cation intermediate. The study has shown that the activation of propellane cTc-c bonds with strong oxidizing electrophiles occurs by a sequence of single-electron transfer steps. These findings are supported by ab initio computations showing that the isomeric radical cations can equilibrate with low barriers and lead to a common product. ... 

In an irreversible reaction, the rate controlling process is usually a single electron transfer step with a rate determined by Equation 1.8. The corresponding po-larographic wave is then described by Equation 1.18 where kconv is the rate constant for electron transfer at the potential of the reference electrode. For an irreversible... 

Electron transfer through a molecular bridge can occur by single or multiple-step mechanisms [5-7]. The multiple steps may involve real (hopping) or virtual (superexchange) bridging states. Single electron transfer steps... 

Role of Single-Electron Transfer Steps in Reactions of Organic Compounds L. A. Blyumen-fel d et al, Zh. Fiz. Khim., 1970, 44, 931-944. 

Fig. 4. Schematic representation of the effect of a change in electrode potential, E, on the free energy—reaction coordinate curves for a heterogeneous single electron transfer step (O + n e - R) at two different electrode potentials (1) E = Ee (solid line) and (2) E

An example of transfer of electron from nucleophile to substrate is seen in the formation of the radical anions (observable by ESR) of 5-halo-2A/,3W-benzotf>]thiophene-2,3-diones on treatment with nucleophiles.20 It has been proposed in some cases, that this single-electron transfer step takes place through a charge transfer complex between the nucleophile and the aromatic substrate.21-22 Some reactions occur spontaneously, i.e. without any catalysts or reagents other than the substrate and the nucleophile, but the initiation process is usually, although not invariably, photostimulated (near-ultraviolet radiation, 300-... 

The propagation steps in the SrnI sequence are the dissociative step (equation 2), the associative step (equation 3), and the single-electron transfer step (equation 4). These processes are discussed extensively in Chapter 8 of ref. 18. The nature of the nucleofuge is critical in that poor nucleofuges retard the dissociation of the intermediate radical anion, ArX-- (equation 2), and prevent the reaction from proceeding at a reasonable rate or stop it completely (see Section 2.2.2.3). 

A central preoccupation of electron-transfer models is to provide estimates of the activation free energy of a single electron-transfer step, AG, from the structural and thermodynamic properties of the system [31]. Two key features of these models should be noted at the outset. Firstly, as noted above, it is advantageous to separate AG into intrinsic and thermodynamic components according to [cf. eqn. (6)]... 

For solution reactants, the intrinsic barrier can be most directly related to the work-corrected standard rate constant for the single electron-transfer step... 

Relatively more attention was paid to direct N- and C-vinylation of the pyrrole moiety by acetylene and its electron-deficient derivatives in the latter case a single electron transfer step has been detected. 

For ECE or DISP mechanisms, the parameter usually measured as a function of the convective mass transport parameter is the effective number of electrons transferred, N ff, which for two single-electron transfer steps varies between one and two as described above. 

Several of the reductases mentioned here belong to the same structural family (the FNR family), and they are mechanistically related to each other (9). A two-electron reduction of the flavin by NAD(P)H in these enzymes typically involves the transient formation of an oxidized flavin-reduced pyridine nucleotide charge-transfer complex, which is followed by hydride transfer. After reduction, the flavin can transfer its electrons to different redox partners. With NADH cytochrome b5 reductase, this transfer occurs in separate single-electron transfer steps. With... 

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