Abstraction single electrons

At the same time, the acidic sites of MMT may turn out to be sufficiently active to abstract single electrons from donor molecules with formation of free radicals, the latter being capable of further accelerating the thermal oxidation of PE chains e. g. by virtue of branching reactions. 

FIGURE 4.51 Mechanism for cytochrome P450-catalyzed N-dealkylation via an initial single electron pathway, SET, or via the hydrogen atom abstraction pathway, HAT. 

The reactions of sodium dimethyl and diisopropyl phosphite with 4-nitrobenzyl chloride, 9-chlorofluorene, and diphenylchloromethane provided information that supported the proposed reaction mechanism. The RaPO anion acts towards an arylmethyl chloride as a base and abstracts a proton to form a carbanion, which can then participate in single-electron transfer processes to produce carbon-centred radicals. ... 

This chapter considers ion-radicals with detained and released single electrons. Some ion-radicals contain fragment orbitals that suspend an unpaired electron preferentially. Other ion-radicals are characterized by the delocalization of an unpaired electron along orbitals, which encompass the whole molecular framework more or less evenly. This chapter considers the material, comprised from this point of view, using the terms detained and released electron. Such an abstraction helps us to analyze these two intrinsic features of organic ion-radical reactivity. 

The hydroxyl radical can also abstract a single electron from dG to generate the base radical cation (G ). In duplex DNA, the G " " will be stabilized by its delocalization into adjacent bases. Both calculations and kinetic measurements " indicate that GG sequences have a lower oxidation potential than an isolated G. Nucleo-bases on the 3 -side of G determine the extent of G formation, and here purines are more effective than pyrimidines at lowering the oxidation potential of G, which accounts for the GG effect and that GA sites are also reactive. ... 

Abstract. We present a quantum-classieal determination of stable isomers of Na Arii clusters with an electronically excited sodium atom in 3p P states. The excited states of Na perturbed by the argon atoms are obtained as the eigenfunctions of a single-electron operator describing the electron in the field of a Na Arn core, the Na and Ar atoms being substituted by pseudo-potentials. These pseudo-potentials include core-polarization operators to account for polarization and correlation of the inert part with the excited electron . The geometry optimization of the excited states is carried out via the basin-hopping method of Wales et al. The present study confirms the trend for small Na Arn clusters in 3p states to form planar structures, as proposed earlier by Tutein and Mayne within the framework of a first order perturbation theory on a "Diatomics in Molecules" type model. 

Initiation. Initiation generates a reactive intermediate. A chlorine atom is highly reactive because of the presence of an unpaired electron in its valence shell. It is electrophilic, seeking a single electron to complete the octet. It acquires this electron by abstracting a hydrogen atom from methane. 

A novel synthesis of 5,6-dihydro-4//-1,2-oxazines (20) is presented via the photo-induced cyclization of y. d-unsaturated oximes (21) see Scheme 4. Irradiation of (21) in the presence of 9,10-dicyanoanthraccnc (DCA) led to the heterocycle (20) only. The proposed mechanism proceeds via the radical cation (22), generated by single-electron transfer (SET) from the oxime (21) to the excited sensitizer (DCA. Cyclization of (22) affords the oxazine (20) after proton transfer to the DCA radical anion (DCA ) and H abstraction.61... 

Two mechanisms were proposed for the (3-lactam-forming photoreactions, one radical involving excited-state H-atom abstraction while the other following a sequential single-electron-transfer (SET)-proton-transfer route. 

Triplet oxygen is a stable and surprisingly unreactive electrophilic diradical. Its reactions with organic compounds (autoxidation) include abstraction of hydrogen atoms or single electrons and addition to reactive C-C double bonds (Scheme 3.14). 

Scheme 3.18. Oxidation of arenes via abstraction of single electrons [72].

The photoreactions of iV-(trimethylsilyl)methyl- or iV-(tributylstannyl)methyl-substituted a-ketoamides resulted into the formation of complex mixtures including azetidin-2-ones and oxazolidinones with or without the trimethylsilyl or tributylstannyl moiety <2004JOC1215>. It was observed that the reaction of A-(trimethylsilyl)methyl-substituted a-ketoamides proceeded by competitive hydrogen abstraction and sequential single electron transfer (SET)-desilyla-tion pathways, whereas the reaction of iV-(tributylstannyl)methyl-substituted a-ketoamides preferred the sequential SET-destannylation pathway. 

Single-electron oxidants such as Mn3+, Cu2+, and Fe3+ abstract one electron from the substrates to produce carbon-centered radicals, as shown in eq. 1.6. 

Especially for alkyl halides 6 the transfer of a single electron from the metal center is facile and occurs at the halide via transition state 6C, which stabilizes either by direct abstraction of the halide to a carbon-metal complex radical pair 6D or via a distinct radical anion-metal complex pair 6E. This process was noted early but not exploited until recently (review [45]). Alkyl tosylates or triflates are not easily reduced by SET, and thus Sn2 and/or oxidative addition pathways are common. The generation of cr-radicals from aryl and vinyl halides has been observed, but is rarer due to the energy requirement for their generation. Normally, two-electron oxidative addition prevails. 

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