Electron transfer radical anions

Our early work examined the reaction of PCTFE with sulfur, selenium and phosphorous nucleophiles 9 to achieve high levels of functionalization through a well-precedented (in the case of perfluoroalkyl iodides)20"24 one electron transfer, radical anion chain process. While such a reaction demonstrated the feasibility of using one-electron processes for the functionalization of PCTFE, the carbon-sulfur linkage remained susceptable to oxidation. 

An intramolecular electron-transfer/radical anion mechanism has been advocated for the Truce-Smiles-type rearrangement of t-butyl aryl sulphones by Bu"Li at —78 C, orf Ao-lithiation of the aryl moiety being followed by migration of the t-butyl group to the metallated site. Other methods of C—S bond cleavage that are covered in recent papers include photolysis and electrochemical reduction, ... 

Rathore et al. (2006) studied the intramolecular single-electron transfer in anion-radicals formed from fluorenylidene derivatives. The derivatives used for the reduction were Me— Flu—CH2—Flu—CH2—Flu—CH2—Flu—Me and its deuterated analog, Me—Flu—CH2—(Flu-d8)— CH2—(Flu-dj)—CH2—Flu—Me. Each parent compound initially gave an anion-radical in which an unpaired electron was tunneled between the two internal Flu nuclei and then occured within the outer Flu nuclei. In the outer part, coordinative solvation of the anion-radical by HMPA proceeded much more effectively because of ready space accessibility. Such a solvation provides a driving force for electron tunneling. As the solution electron affinities of perdeuterated aromatic hydrocarbons are less than those of perprotiated hydrocarbons, the electron tunneling was found to be at least an order of magnitude faster only in the case of [Me—Flu—CH,—(Flu-do)—CH,— (Flu-d8)-CH2-Flu-Me]-. ... 

The reduction of a quinone requires two electrons, and it is possible that these electrons could be transferred either together or one at a time. The product of a single-electron transfer leads to what appropriately is called a semiquinone, 1, with both a negative charge and an odd electron (a radical anion) ... 

Fig. 17.85. Mechanistic analysis of the second part of the reaction process where the treatment of the acetoxy sul-fones syn- and anti-A with sodium amalgam completes the Julia-Lythgoe olefination. Series of a first electron transfer (—> alkenyl phenylsulfone radical anion E), homolysis (—> alkenyl radical G + sodium benzene sulfinate), second electron transfer (—> alkenyl anion trans"-D) and in-situ protonation.

Further functionalizations are obtained via the electron transfer— radical cation fragmentation pathway a typical example is side-chain nitration by irradiation of methyaromatics with tetranitromethane. Aromatics form charge-transfer complexes with C(N02)4 irradiation leads to electron transfer and fragmentation of the C(N02)4 radical anion to yield the triad [Ar + C(NO)J N02], followed by combination between the arene radical cation and the trinitromethanide anion. Thus, cyclohexadienes are formed that generally eliminate and rearomatize at room temperature yielding ring-functionalized products [234] (Sch. 21). 

Pulse radiolysis in chlorinated solvents leads to the formation of radical cations of almost all organic compounds including aryls. In most non-halogenated solvents, pulse radiolysis results in the formation of solvated electrons and radical anions of the solute. Therefore, depending on the selected solvent, the same donor-acceptor system could be used for the electron and hole transfer studies. 

By electron transfer radical ions, anions, cations, and radicals can be generated as reactive intermediates. Radical ions are mostly products of outer sphere electron transfer [Eq. (1)] ... 

Because of the radical mechanism for SET reactions, introduction of both a perfluoroalkyl group and a heteroatom moiety to the carbon-carbon double [17-20] and even triple [21] bonds is possible. The initially generated perfluoroalkyl radicals add first to olefins to form a new radical intermediate (23), which then couples with anions (22) to form new anion radicals (24). The formation of the product (25) and the chain propagation via electron transfer from anion radicals (24) to perfluoroalkyl halides constitutes a chain reaction as shown in Scheme 2.38. Sulfur [19], selenium [20], tellurium [21], and phosphorus [22] anions (22) have been employed for these reactions [23]. 

KEYWORDS carbon dioxide radical anion vacuum ultraviolet irradiation electron transfer radical addition phenol toluene benzene chlorobenzene benzaldehyde benzoic acid... 

In conclusion, do the similarities and differences in the reactivity patterns for these reactive species with organic halides indicate a basic relationship or are these similarities fortuitous and does nature provide distinct pathways of comparable energy. Of the three mechanistic possibilities considered for radical anions, electron transfer, radical-like and nucleophic substitution, electron transfer is indicated for highly exothermic reactions, and a radical-like process is likely for the less... 

The most important feature of gamma and electron radiation is that the energy of the radiation is sufficiently high to cause ionization of the substrate molecules through ejection of an electron from the valence shell to leave the parent radical cations, Pt. The electrons may be trapped at acceptor sites to form radical anions, P". Energy transfer from the radiation which is insufficient to produce ionization results in excitation of the polymer molecules, P. Recombination of electrons or radical anions with radical cations also produces excited molecules. 

Hydride abstraction from (7) with trityl perchlorate does not give the dication (8), but rather the monocation (9) resulting from deprotonation of (8). C n.m.r. spectroscopy reveals that the central carbon possesses a considerable amount of electron density, indicating that the dipolar form (9a) makes a significant contribution. There is evidence that formation of dicyclopropene from cyclopropenyl cations under conditions of two-electron reduction proceeds through coupling of cyclopropenyl radicals produced by electron transfer from anion to cation. 

M.p. 296 C. Accepts an electron from suitable donors forming a radical anion. Used for colorimetric determination of free radical precursors, replacement of Mn02 in aluminium solid electrolytic capacitors, construction of heat-sensitive resistors and ion-specific electrodes and for inducing radical polymerizations. The charge transfer complexes it forms with certain donors behave electrically like metals with anisotropic conductivity. Like tetracyanoethylene it belongs to a class of compounds called rr-acids. tetracyclines An important group of antibiotics isolated from Streptomyces spp., having structures based on a naphthacene skeleton. Tetracycline, the parent compound, has the structure ... 

Figure C3.2.10.(a) Dependence of electron transfer rate upon reaction free energy for ET between biphenyl radical anions and various organic acceptors. Experiments were perfonned with the donors and acceptors frozen into...

Step 1 Electron transfer from sodium to the alkyne The product is an anion radical ... 

Step 3 The cyclohexadienyl radical produced m step 2 is converted to an anion by electron transfer from sodium H H... 

Sodium naphthalene [25398-08-7J and other aromatic radical anions react with monomers such as styrene by reversible electron transfer to form the corresponding monomer radical anions. Although the equihbtium (eq. 10)... 

Subsequent studies (63,64) suggested that the nature of the chemical activation process was a one-electron oxidation of the fluorescer by (27) followed by decomposition of the dioxetanedione radical anion to a carbon dioxide radical anion. Back electron transfer to the radical cation of the fluorescer produced the excited state which emitted the luminescence characteristic of the fluorescent state of the emitter. The chemical activation mechanism was patterned after the CIEEL mechanism proposed for dioxetanones and dioxetanes discussed earher (65). Additional support for the CIEEL mechanism, was furnished by demonstration (66) that a linear correlation existed between the singlet excitation energy of the fluorescer and the chemiluminescence intensity which had been shown earher with dimethyl dioxetanone (67). 

Examples include luminescence from anthracene crystals subjected to alternating electric current (159), luminescence from electron recombination with the carbazole free radical produced by photolysis of potassium carba2ole in a fro2en glass matrix (160), reactions of free radicals with solvated electrons (155), and reduction of mtheiiium(III)tris(bipyridyl) with the hydrated electron (161). Other examples include the oxidation of aromatic radical anions with such oxidants as chlorine or ben2oyl peroxide (162,163), and the reduction of 9,10-dichloro-9,10-diphenyl-9,10-dihydroanthracene with the 9,10-diphenylanthracene radical anion (162,164). Many other examples of electron-transfer chemiluminescence have been reported (156,165). 

Under optimum conditions electron transfer can produce excited states efficiently. Triplet fluoranthrene was reported to be formed in nearly quantitative yield from reaction of fluoranthrene radical anion with the 10-phenylphenothia2ine radical cation (171), and an 80% triplet yield was indicated for electrochemiluminescence of fluoranthrene by measuring triplet sensiti2ed isomeri2ation of trans- to i j -stilbene (172). 

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