Electron accepting reaction

As discussed in detail in Section 7.4, the energy liberated by a redox reaction depends on the redox potential of the electron-donating half-cell reaction, relative to the electron-accepting reaction. In the calculation results, we can trace the redox... 

A reaction in which an electron transfer takes place between two different chemical particles is called a redox reaction this is a combination of an dectron donating reaction and an electron accepting reaction as shown in Eqn. 2-40. The reaction in which a chemical particle donates electrons is called the oxidation, and the particle produced by the oxidation is an oxidant while on the other hand the electron accepting reaction is called the reduction, and its product particle is called a reductant. 

Lovley DR, Goodwin S. 1987. Hydrogen concentration as an indicator of the predominant terminal electron-accepting reactions in aquatic sediments. Geochimica et Cosmochimica Acta 52 2953-3003. 

TABLE 7-11 Electron Acceptance Reactions (Reduction Reactions) (Energy-Producing Reactions) in Aerobic and Anaerobic Systems... 

Microbial Fe(III) and Mn(IV) reduction in soils presents a unique problem relative to other terminal electron-accepting reactions (e.g., oxygen, nitrate, and sulfate reduction) because Fe(III) and Mn(IV) oxides are highly insoluble at circumneutral pH. As a result, the reduction process involves physical contact and the interaction of bacterial cell surfaces with particulate oxide phases that are not transported into the cell (Lovley, 1987 Ghiorse, 1988). The need for this interaction depends on the organism, the electron donor, and the form of Fe(lll). 

Amines are powerful nucleophiles which react under neutral or slightly basic conditions with several electron-accepting carbon reagents. The reaction of alkyl halides with amines is useful for the preparation of tertiary amines or quaternary ammonium salts. The conversion of primary amines into secondary amines is usually not feasible since the secondary amine tends towards further alkylation. 

Weak to moderate chemiluminescence has been reported from a large number of other Hquid-phase oxidation reactions (1,128,136). The Hst includes reactions of carbenes with oxygen (137), phenanthrene quinone with oxygen in alkaline ethanol (138), coumarin derivatives with hydrogen peroxide in acetic acid (139), nitriles with alkaline hydrogen peroxide (140), and reactions that produce electron-accepting radicals such as HO in the presence of carbonate ions (141). In the latter, exemplified by the reaction of h on(II) with H2O2 and KHCO, the carbonate radical anion is probably a key intermediate and may account for many observations of weak chemiluminescence in oxidation reactions. 

It is known that the ability of nitrotolane to cyclize depends on electronic factors (69MI2) hence l,3-dimethyl-4-nitro-5-phenylethynylpyrazole, whose acetylene group is in the most electron-accepting position of the pyrazole ring, i.e., favorable for nucleophilic addition, was introduced into the reaction of cyclization. Thus,... 

It should be expected that the orientation and rate of electrophilic substitution in the isoxazole nucleus would be affected by both hetero atoms. Because of the electron-accepting effect of the nitrogen atom, electrophilic substitution of the isoxazole nucleus should proceed less readily than in the case of benzene and should occur essentially at the position jS to the nitrogen atom, just as in pyridine and other azoles. Simultaneously the electron-donating oxygen atom should facilitate such reactions in isoxazole as compared with the substitution in pyridine. These predictions are confirmed by the available experimental evidence. 

Thus the activity of the methyl groups in this reaction decreases in the series C-4 > C-5 > C-3. This may be considered as evidence of the inhibiting effect of the nitrogen hetero atom on the radical substitution in methyl groups at C-3 and, to a lesser extent, at C-5 (compare the effect of the heterocyclic nitrogen in the pyridine and azole series ) and of a similar effect of the electron-accepting substituents in the 4-position on the methyl group at C-5. 

Wydeven [865] concludes that, in the presence of Co304 (6.8%), up to 60% of the reactant NaC103 decomposed in the solid state. During subsequent melting, there was an increase in reaction rate. The catalytic activity of the additive was ascribed to the electron accepting properties of the oxide (Co304 is a p-type semi-conductor). The apparent value of E increased from 120 to 200 kJ mole 1 between a = 0.05 and 0.5. 

In principle, sulfonyl compounds bearing highly-electron-accepting substituents are able to transfer the sulfonyl group as an electrophile. Thus, the exchange of aryl substituents in methyl aryl sulfones under catalysis of trifluoromethanesulfonic acid takes place258 (equation 46). This reaction represents a further example for the reversibility of Friedel-Crafts reactions. 

In many cases, the values of A n and k2i may be directly or indirectly determined. We shall say no more about this relationship here, other than to indicate that it proves to be generally applicable, and is sufficiently accepted that the Marcus-Hush equation is now used to establish when an outer-sphere pathway is operative. In the context of this chapter, the involvement of the Kn term is interesting for it relates to the relative stabilization of various oxidation states by particular ligand sets. The factors which stabilize or destabilize particular oxidation states continue to play their roles in determining the value of Kn, and hence the rate of the electron transfer reaction. 

Photochemical reactions of carbonyl compounds with alkenes give the oxetanes (Scheme 30). The stereochanical course depends on the substituents of the alkenes [16]. The reactions proceed with the retention of the configuration of the alkenes for the electron accepting substituent, e.g., CN. The stereochemical integrity is lost for the donating group, e.g., OCH. ... 

Scheme 30a,b [2 + 2] Cycloaddition reactions of excited carbonyl compounds with the alkenes substituted by electron-accepting (a) and -donating (b) groups... 

Thermal [2h-2] cycloaddition reactions of carbonyl compounds were catalyzed by a Lewis acid. The catalyst forms complexes with the carbonyl compounds and enhances the electron-accepting power. The reaction shifts from the delocalization band to the pseudoexcitation band. Catalyzed [2h-2] cycloaddition reactions were observed with acetylenic compounds [28] and ketenes [29-31]. 

The theory of the mechanistic spectrum generally snggests that photochemical reactions between donors and acceptors in the delocalization band could be similar to thermal reactions between strong donors and acceptors in the pseudoexcitation band. This is fnrther snpported by the reactions of indoles with electron-accepting... 

The pseudoexcitation is induced by the delocalization from alkenes to the Si(100)-2 X 1 surface [133]. Electron-accepting alkenes undergo different reactions. For acrylonitirile, a [4+2] cycloaddition reaction was found to be kinetically most favorable [135]. 

A pair of reactions of 1,4-dihydropyridines with electron-accepting alkenes (Scheme 31) shows experimental evidence for the mechanistic spectrum between the pseudoexcitation and transfer bands. Acrylonitrile undergoes an ene reaction [143] (Scheme 31a). This is a reaction in the pseudoexcitation band. A stronger acceptor, alkylidene- and arylmethylydenemalonitriles are reduced [144] (Scheme 31b). This is a reaction in the transfer band, where a hydride equivalent shifts without bond formation between the ti bonds of the donors and acceptors. 

Danshefsky s diene [19] is the 1,3-butadiene with amethoxy group at the 1-position and a trimethylsiloxy group at the 3-position (Scheme 18). This diene and Lewis acids extended the scope of hetereo-Diels-Alder reactions with aldehydes [20], This diene reacts with virtually any aldehyde in the presence of Lewis acids whereas dienes usually react with only selected aldehydes bearing strongly electron accepting a-substituents. There are two (Diels-Alder and Mukaiyama aldol) reaction pathways (Scheme 18) identified for the Lewis acids catalyzed reactions of Danishefsky diene with aldehydes [21, 22]. The two pathways suggest that these reactions occur on the boundary between the delocahzation band (the pericyclic... 

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