Electron spin resonance alkyl radicals

Fessenden R W and Schuler R H 1963 Electron spin resonance studies of transient alkyl radicals J. Chem. Phys. 39 2147-95... 

D. J. Edge and J. K. Kochi, Effects of halogen substitution on alkyl radicals conformational studies by electron spin resonance. J. Am. Chem. Soc. 94(18), 6485-6495 (1972). 

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-... 

The partition of the dimerization yields at 77 °K. into RPD and DD yields is shown in Table VIII. DD was obtained at 20°C. from the yields in the presence of added I2 and at 77 °K. by utilization of the efficiency factor equal to 2.3. Note the low yields at 20°C. for products of secondary radical combinations. We postulate that the intermediate excited primary radicals formed after neutralization in the UPD mechanism at 77 °K. may rearrange to secondary radicals before the final cross bond is formed. Evidence for this postulate is indicated in Table VIII by the observation that the n-C12 and 5-MeCu yields appear to be almost entirely due to the DD mechanism. Such isomerization of primary to secondary alkyl radicals in the solid phase at —196 °C. has recently been observed by electron spin resonance.62... 

Bauer G (2000) Reactive oxygen and nitrogen species efficient, selective and interactive signals during intercellular induction of apoptosis. Anticancer Res 20 4115-4140 Beckwith AU, Davies AG, Davison IGE, Maccoll A, Mruzek MH (1989) The mechanisms of the rearrangements of allylic hydroperoxides 5a-hydroperoxy-3p-hydrocholest-6-ene and 7a-hydro-peroxy-3(1-hydroxycholest-5-ene. J Chem Soc Perkin Trans 2 815-824 Behar D, Czapski G, Rabani J, Dorfman LM, Schwarz HA (1970) The acid dissociation constant and decay kinetics of the perhydroxyl radical. J Phys Chem 74 3209-3213 Benjan EV, Font-Sanchis E, Scaiano JC (2001) Lactone-derived carbon-centered radicals formation and reactivity with oxygen. Org Lett 3 4059-4062 Bennett JE, Summers R (1974) Product studies of the mutual termination reactions of sec- alkylper-oxy radicals Evidence for non-cyclic termination. Can J Chem 52 1377-1379 Bennett JE, Brown DM, Mile B (1970) Studies by electron spin resonance of the reactions of alkyl-peroxy radicals, part 2. Equilibrium between alkylperoxy radicals and tetroxide molecules. Trans Faraday Soc 66 397-405... 

Although the results of electron-spin resonance studies of alkyl substituted radicals and radical-ions are of great significance to the study of hyperconjugation (Symons, 1962), it seems that little attention has been paid to the results by workers primarily concerned with hyperconjugation rather than with free radicals. Thus in a recent conference on hyperconjugation (Tetrahedron, 1959) references to electron-spin resonance results were notable by their complete absence. 

Electron Spin Resonance Parameters for the Stable Group IV Tris(alkyl) and Tris(amido) Radicals 1... 

Trimethylsilyl anions also give the substitution products by the reaction with alkyl chloride in almost quantitative yield (equation 14), but considerable amounts of electron-transfer products are produced as well in HMPA. Indeed, Mc3SiNa/HMPA is an excellent reagent to produce anion radicals (Table 9) from aromatic hydrocarbons for ESR (electron spin resonance) studies (equation 65). ... 

The reaction of thietane with A7-chlorosuccinimide to give 102 may proceed via attack of a nitrogen radical on sulfur, but an ionic mechanism via an 5-halo-sulfonium salt intermediate is also possible. Alkoxy radicals attack the sulfur atom of thietanes to give ring-opened alkyl radicals 103 whose electron-spin resonance spectra have been obtained. Trifluoromethylthio and other sulfur... 

This leads to a hydroperoxide and an alkyl radical, which can again react with oxygen according to Reaction (4.2). The rate of Reaction (4.3) is slow, ks = 10 -10 1 mor s at 30°C, dependent on the type of hydrocarbon, when compared with Reaction (4.2), and is therefore the rate-determining step for chain propagation. Due to their low reactivity, peroxy radicals are present in relatively high concentration in the system when compared with other radicals, determined via electron spin resonance. 

A sextet has been observed in the electron spin resonance spectrum of irradiated polyethylene at 77°K [31, 32] and assigned to the central radical (II). Moreover, five hyperfine components have been detected and attributed to the terminal radical (I) [32]. According to Ranby and Yoshida [32] free radicals (I) and (II) are formed in primary photochemical processes by fission of C—C and C—H bonds. Such a conclusion seems, however, doubtful in the light of the chemical evidence presented above which supports the initiation of the photodegradation of polyethylene by adventitious impurities. Moreover Tsuji and Takeshita [33] have recently observed that alkyl radicals produced at liquid nitrogen temperature by ultraviolet irradiation of polyethylene in vacuo are transformed into transient acyl radicals when the sample is allowed to warm up to about—125°C ... 

When polyethylene is irradiated at room temperature, allyl and polyenyl type free radicals are formed (2) and are much more stable than alkyl type free radicals (7, 13). Electron spin resonance (ESR) experiments have demonstrated that the allyl or polyenyl free radicals are quite stable, persisting for relatively long periods (hours or days)... 

Reactions of lithium alkyls are generally considered to be carbanionic in nature, but in reactions with alkyl halides free radicals have been detected by electron spin resonance.32 Lithium alkyls are widely employed as stereospecific catalysts for the polymerization of alkenes, notably isoprene, which gives up to 90% of 1,4-cA-polyisoprene numerous other reactions with alkenes have been studied.33 The TMED complexes again are especially active not only will they polymerize ethylene but they will even metallate benzene and aromatic compounds, as well as reacting with hydrogen at 1 atm to give LiH and alkane. 

Electron Spin Resonance (ESR) Observation of Radical Migration Reactions in the Polymerization of Alkyl Acrylates... 

Davies et al. (1971b) also studied the reactions of I-C4H90, prepared from (r-C4H90)2 photolysis, with boron compounds in competition with the reaction with cyclopentane in peroxide or isooctane solutions. They monitored the radicals produced from the respective reactions by electron spin resonance. The reactions of I-C4H90 with boron compounds had rate coefficients of 2 X 10 — 3 X 10 A/ -sec at 30 C. This work was extended by Davies et al. (1972a), who used r-butylhypochlorite as the source of I-C4H90 radicals and measured the amount of alkyl chlorides produced from the alkyl radical products at 40°C. 

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