Electron abstraction

Oxidation reactions include electron abstraction, mtroduction of hydroxyl and 0X0 groups, and destruction of the carbon skeleton... 

Hydroxy Benzophenone N(CH3)2 3-N,N -Dimethylamino Phenoxy Electron Abstraction, Followed by Proton Migration Photocrosslinking" ... 

This is in accordance with the primary kinetic isotope effect for Mn(III) sulphate With Co(III) electron abstraction may occur to give a radical-cation which suffers further oxidation. The alternative explanation of the lack of an isotope effect is that formation of the Co(III)-ketone complex is rate-determining this lacks, however, other kinetic support . ... 

The remarkable inertness of dialkyl ethers to one-equivalent oxidants is good evidence that the readier oxidation of alcohols involves more than simple electron abstraction. Di-isopropyl ether is oxidised by Co(III) in CH3CN-H2O mixtures with complicated kinetics individual runs show first-order decay of Co(III) but the rate coefficients increase with increasing [Co(III)], and the order with respect to substrate is less than one but is neither fractional nor of a Michaelis-Menten type. The main product is acetone and the following reaction sequence is proposed... 

Purified ligninase H8 produced by P. chrysosporium in stationary cultures oxidized pyrene to pyrene-1,6- and pyrene-l,8-quinones in high yield, and experiments with showed that both quinone oxygen atoms originated in water (Figure 8.25). It was suggested that initial one-electron abstraction produced cation radicals at the 1 and 6 or 8-positions (Hammel et al. 1986), whereas in... 

Bieber reported that the reaction of bromoacetates is greatly enhanced by catalytic amounts of benzoyl peroxide or peracids and gives satisfactory yields with aromatic aldehydes. A radical chain mechanism, initiated by electron abstraction from the organometallic Reformatsky reagent, is proposed (Scheme 8.27).233 However, an alternative process of reacting aldehydes with 2,3-dichloro-l-propene and indium in water followed by ozonolysis provided the Reformatsky product in practical yields.234 An electrochemical Reformatsky reaction in an aqueous medium and in the absence of metal mediator has also been reported.235... 

In this case the radical 85 is probably formed from the N-methyl-9-cyanoacridanyl anion 84 by electron abstraction by oxygen ... 

LiP catalyze several oxidations in the side chains of lignin and related compounds [26] by one-electron abstraction to form reactive radicals [27]. Also the cleavage of aromatic ring structures has been reported [28]. The role of LiP in ligninolysis could be the further transformation of lignin fragments, which are initially released by MnP. 

However, Bawn et al., take the view that when polymerization of an alkyl vinyl ether is initiated by a stable ion, such as tropylium, the initiation involves electron abstraction from the monomer with formation of a radical cation and a tropyl radical [52] ... 

In order to assess reactivity in this context we need first to recognise that the chemical initiation of cationic polymerizations can occur in different ways. Disregarding the rarer initiations involving electron abstraction or hydride abstraction from a monomer, the most common are... 

Barsberg, S. (2002). Modification phenomena of solid-state lignin caused by electron-abstracting oxidative systems. Archivei of Biochemistry and Biophysics, 404(1), 62-70. 

De Queiroz et al. (2006) performed mass-spectrometric experiments in which gas-phase reactions of the isolated N02 and benzene derivatives were studied. The reaction results in the predominant electron abstraction yielding exclusively ionized benzenes. None of the expected adducts (such as a complexes) were observed. Probably because direct addition of NO, to benzene is strongly exothermic, the nascent product is too hot to survive when it is isolated in the gas phase. 

Characterization of the R2NO transient species becomes then possible through the EPR . As an alternative to the electrochemical one-electron abstraction, chemical oxidants such as Pb(OAc)4 or Ce + salts have been analogously employed in order to generate the R2NO species . 

A possible reductive role for veratryl alcohol oxidase is proposed in Figure 5. Laccases from C. versicolor can produce both polymerization and depolymerization of lignin (29). In phenolic lignin model dimers, laccase can perform the same electron abstraction and subsequent bond cleavage as found for lignin peroxidase (30). The phenolic radical is however likely to polymerize unless the quinoid-type intermediates can be removed, for example by reduction back to the phenol. Veratryl alcohol oxidase, in... 

In double-stranded DNA, electron abstraction from the guanine radical cation can be associated with an extremely fast shift of the N1 proton to its Watson-Crick partner cytosine (Scheme 2a) [9]. The equilibrium constant for the protonation of C (pfCa=4.3) with the concomitant deprotonation of G estimated from the pK values of the free nucleosides, is about 2.5 [49]. Within these constraints, the guanine radical should retain some radical cation character [82] and the complete deprotonation of G would require a base pair opening event occurring on a millisecond timescale [74]. An alternative mechanism of G deprotonation is the release of the N2 proton (Scheme 2b). This mechanism was experimentally established for 1-methyl-guanosine conductometric results showed that in neutral solutions, the radical cation of this nucleoside rapidly deprotonates with the formation of the neutral radical [48]. Although the exact mechanism of the G deprotonation in double-stranded DNA requires further clarification, electron abstraction... 

In neutral aqueous solutions, the ultimate product of one-electron abstraction from guanine is the guanine neutral radical. In DNA, this radical is formed via the deprotonation of the guanine radical cation arising, e.g., from hole localization or directly via proton-coupled electron transfer from guanine to an appropriate electron acceptor. The G(-H) radicals do not exhibit observable reactivities with molecular oxygen (fc<10 s ) [93]. 

As in Section IV for naphthalene vapor, the kinetic spectra of solids are presented by plotting on the abscissa axis the quantity Ep = (hv — incident photon,

work function of the solid (energy of electron abstraction). Ekin is the photoelectron kinetic energy, which is lower than the theoretical upper energy limit of kinetic energy because of internal energy... 

The energy required to extract an electron from the organic solid to a point in vacuum outside its surface, i.e., the work function

maximum kinetic energy as function of the photon energy. The remarkable constancy of the work function, which is independent of the photon energy, leads to the following conclusions (1) the probability of the electron abstraction from the solid does not vary with the photon energy ... 

The four electrons abstracted from water do not pass directly to P680+, which can accept only one electron at a time. Instead, a remarkable molecular device, the oxygen-evolving complex (also called the watersplitting complex), passes four electrons one at a... 

The mechanism of the reaction of thiophene with a variety of radicals as a function of pH has been studied using ESR (81JCS(P2)207). Attack by -OH at pH 6 proceeds by direct addition with a preference to add to the a-position the ratio of (226) to (227) is 4 1. At low pH the (3-adduct easily loses OH- to form the thiophene radical-cation, which may undergo rehydration. In the case of 2-methyIthiophene the radical-cation deprotonates to give the thenyl radical this is reminiscent of the electrochemical oxidation (Section 3.14.2.6). The radical-cations are also formed by direct electron abstraction from the thiophene substrates by chlorine anion-radicals. At pH >6, (226) starts disappearing with formation of ring-opened products (Scheme 61). 

---