Electron spin resonance radical formation

The idea of having a two-dimensional peroxide or hydroperoxide form is not completely unbelievable since it has been observed on a ZnO surface. Kokes 49), using electron spin resonance, observed formation of radical fragments by H2O2 when hydrogen and oxygen were used to dope a ZnO catalyst. 

By using this technique acrylamide, acrylonitrile, and methyl acrylate were grafted onto cellulose [20]. In this case, oxidative depolymerization of cellulose also occurs and could yield short-lived intermediates [21]. They [21] reported an electron spin resonance spectroscopy study of the affects of different parameters on the rates of formation and decay of free radicals in microcrystalline cellulose and in purified fibrous cotton cellulose. From the results they obtained, they suggested that ceric ions form a chelate with the cellulose molecule, possibly, through the C2 and C3 hydroxyls of the anhy-droglucose unit. Transfer of electrons from the cellulose molecule to Ce(IV) would follow, leading to its reduction... 

Thermal analyses of the sodium salts of several sulphuroxyacids, including some non-isothermal kinetic data, have been reported [813], Evidence for the formation of SOi radicals during such reactions has been obtained [348] by electron spin resonance measurements. 

This color transformation has been observed in dibenzo-p-dioxin (Structure I) and in its bromo, chloro, nitro, methyl, and ethyl derivatives in addition, the observed electron spin resonance (ESR) signals indicated the presence of paramagnetic species (2, 3). This phenomenon has been attributed to the formation of cation radicals in acid solution. 

Although Ce(IV) oxidation of carboxylic acids is slow and incomplete under similar reaction conditions , the rate is greatly enhanced on addition of perchloric acid. No kinetics were obtained but product analysis of the oxidations of -butyric, isobutyric, pivalic and acetic acids indicates an identical oxidative decarboxylation to take place. Photochemical decomposition of Ce(IV) carbo-xylates is highly efficient unity) and Cu(ll) diverts the course of reaction in the same way as in the thermal oxidation by Co(IIl). Direct spectroscopic evidence for the intermediate formation of alkyl radicals was obtained by Greatorex and Kemp ° who photoirradiated several Ce(IV) carboxylates in a degassed perchloric acid glass at 77 °K in the cavity of an electron spin resonance spectro-... 

KRISTENSEN D, krOger-ohlsen m V and SKIBSTED L H (2002) Radical formation in dairy products Prediction of oxidative stability based on electron spin resonance spectroscopy, in Morello M J, Shahidi F Ho CT Free Radicals in Food, Chemistry, Nutrition and Health Effects, ACS Symposium Series 807, Washington D C, 114-25. 

X-Ray irradiation of quartz or silica particles induces an electron-trap lattice defect accompanied by a parallel increase in cytotoxicity (Davies, 1968). Aluminosilicate zeolites and clays (Laszlo, 1987) have been shown by electron spin resonance (e.s.r.) studies to involve free-radical intermediates in their catalytic activity. Generation of free radicals in solids may also occur by physical scission of chemical bonds and the consequent formation of dangling bonds , as exemplified by the freshly fractured theory of silicosis (Wright, 1950 Fubini et al., 1991). The entrapment of long-lived metastable free radicals has been shown to occur in the tar of cigarette smoke (Pryor, 1987). 

Tsuchija, J. Niki, E. Kamiya, Y. Oxidation of lipids IV. Formation and reaction of chromanoxyl radicals as studied by electron spin resonance. Bull. Chem. Soc. Jpn. 1983, 56, 229-232. 

Radiation techniques, application to the study of organic radicals, 12, 223 Radical addition reactions, gas-phase, directive effects in, 16, 51 Radicals, cation in solution, formation, properties and reactions of, 13, 155 Radicals, organic application of radiation techniques, 12,223 Radicals, organic cation, in solution kinetics and mechanisms of reaction of, 20, 55 Radicals, organic free, identification by electron spin resonance, 1,284 Radicals, short-lived organic, electron spin resonance studies of, 5, 53 Rates and mechanisms of solvolytic reactions, medium effects on, 14, 1 Reaction kinetics, polarography and, 5, 1... 

Depolymerization of some natural polymers is another typical example. Milling of chitin or chitosan, at ambient temperature, leads to cleavage of the cellulose polymeric chain. Scission of 1,4-glucosidic bonds takes place, and the radicals formed recombine. Based on electron spin resonance, Sasai et al. (2004) monitored both the homolysis and the radical recombination. The recombination led to the formation of midsize polymeric chains only. Some balance was established between the homolytic depolymerization and the size-limited recombination of the radicals primarily formed. 

Thermal decomposition of allylbenzene ozonide (58) at 37°C in the liquid phase gave toluene, bibenzyl, phenylacetaldehyde, formic acid, (benzyloxymethyl)formate, and benzyl formate as products. In chlorinated solvents, benzyl chloride is also formed and in the presence of a radical quench such as 1-butanethiol, the product distribution changes. Electron spin resonance (ESR) signals are observed in the presence of spin traps, adding to the evidence that suggests radicals are involved in the decomposition mechanism (Scheme 9) <89JA5839>. 

The format of this section is similar to that of the review by Knowles <1996CHEC-II(7)489>, where only the main structure elucidation techniques are reviewed. None of the heterocyclic systems included in this chapter exists as radicals thus, electron spin resonance (ESR) spectroscopy is not included. Mass spectrometry is also omitted from discussion, as this technique is always used in conjunction with other analytical techniques to ensure full characterization of compounds. Nevertheless, mass spectra for most of the compounds in this chapter have been reported, although assignments of fragmentation patterns are rarely given. 

Electron spin resonance (ESR) methods have been used to observe the formation of the radical cations and dications of benzoll,2- 4,5- ]bis[l,2,3]trithiole 13 and benzo[l,2-4 4,5- ]bis[l,2,3]dithiazole 17, and the experimental results confirm the ab initio calculations performed <2003EJ04902, 1997JA12136>. ESR has also been used to confirm the formation of superoxides upon photolysis of aryl benzobisthiazoles and aryl benzobisoxazoles in the presence of molecular oxygen <2003MM4699>. 

The formation of ion radicals from monomers by charge transfer from the matrices is clearly evidenced by the observed spectra nitroethylene anion radicals in 2-methyltetrahydrofuran, n-butylvinylether cation radicals in 3-methylpentane and styrene anion radicals and cation radicals in 2-methyltetrahydrofuran and n-butylchloride, respectively. Such a nature of monomers agrees well with their behavior in radiation-induced ionic polymerization, anionic or cationic. These observations suggest that the ion radicals of monomers play an important role in the initiation process of radiation-induced ionic polymerization, being precursors of the propagating carbanion or carbonium ion. On the basis of the above electron spin resonance studies, the initiation process is discussed briefly. 

Although some radicals and cation radicals are postulated for chemical and electrochemical transformations of 2-benzopyrylium cations (Sections III,F,1 and IV,B)> attempts to record their electron spin resonance (ESR) spectra failed, obviously because of a low stability of these radicals. However, the structural combination of hydroxy aryl and 2-benzopyrylium fragments favors the formation of radical cations 301-303, and their ESR spectra were recorded on oxidation of the corresponding 2-benzopyrylium salts with lead tetraacetate (87RRC417). 

Formation of radical anions 109 and 110 from l,l-dimethyl-2,5-diphenylsilole and 1,1-dimethyl-2,3,4,5-tetraphenylsilole164, which are further reduced to the dianions 111 and 112, respectively, has been shown by electron spin resonance and UV-visible spectrometry (equation 62). 

Becker D, Bryant-Friedrich A, Trzasko C-A, Sevilla MD (2003) Electron spin resonance study of DNA irradiated with an argon-ion beam evidence for formation of sugar phosphate backbone radicals. Radiat Res 160 174-185... 

Behrens G, Bothe E, Koltzenburg G, Schulte-Frohlinde D (1980) Formation and structure of 1,1-di-alkoxyalkene radical cations in aqueous solution. An in situ electron spin resonance and pulse conductivity study. J Chem Soc Perkin Trans 2 883-889... 

Heberger K, Lopata A (1998) Assessment of nudeophilicity and electrophilicity of radicals, and of polar and enthalpy effects on radical addition reactions. J Org Chem 63 8646-8653 HerakJN, Behrens G (1986) Formation and structure of radicals from D-riboseand 2-deoxy-D-ribose by reactions with SO4 radicals in aqueous solution. An "in-situ" electron spin resonance study. Z Naturforsch 41c 1062-1068... 

Gilbert BC, Laue HAH, Norman ROC, Sealy RC (1975) Electron spin resonance studies, part 16. Oxidation of thiols and disulphides in aqueous solution formation of RS, RSO, RSO2, RSSR-, and carbon radicals. J Chem Soc Perkin Trans 2 892-900 Gilbert BC, Holmes RGG, Laue HAH, Norman ROC (1976) Electron spin resonance studies. Part L. Reactions of alkoxyl radicals generated from alkylhydroperoxides and titanium (III) ion in aqueous solution. J Chem Soc Perkin Trans 2 1047-1052... 

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