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1.
Absolute rate constants for the addition of the 2-cyano-2-propyl radical to 26 alkenes CH2=CXY at 315 K were determined in solution by time-resolved electron-spin-resonance spectroscopy. They vary with the alkene substituents from 30 M?1 s?1 to 7′010 M?1 s?1. For styrene the temperature dependence is given by log k/M?1 s?1 = 7.7 ? 26.1/Θ where Θ = 2.303 RT in kJ/mol. An analysis of the substituent effects in terms of polar and enthalpic factors reveals a dominant influence of the overall reaction enthalpy. © 1993 John Wiley & Sons, Inc. 相似文献
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Perfluorobutylperoxyl radicals were produced by radiolytic reduction of perfluorobutyl iodide in aerated methanol solutions. Rate constants for the reactions of this peroxyl radical with various organic compounds were determined by kinetic spectrophotometric pulse radiolysis. The rate constants for alkanes and alkenes were determined by competition kinetics using chlorpromazine as a reference. The results indicate that hydrogen abstraction from aliphatic compounds takes place with a rate constant that is too slow to measure in our system (<105 M?1 s?1), and that abstraction of allylic and doubly allylic hydrogens is slow compared with addition. Addition to alkenes takes place with rate constants of the order of k = 106 ? 108 M?1 s?1. Good correlation was obtained between log k and the Taft substituent constants σ* for the various substituents on the double bond. Perfluorobutylperoxyl radical is found to be more reactive than trichloromethylperoxyl and other peroxyl radicals. 相似文献
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Absolute rate constants and their temperature dependencies were determined for the addition of hydroxymethyl radicals (CH2OH) to 20 mono- or 1,1-disubstituted alkenes (CH2 = CXY) in methanol by time-resolved electron spin resonance spectroscopy. With the alkene substituents the rate constants at 298 K (k298) vary from 180 M?1s?1 (ethyl vinylether) to 2.1 middot; 106 M?1s?1 (acrolein). The frequency factors obey log A/M?1s?1 = 8.1 ± 0.1, whereas the activation energies (Ea) range from 11.6 kJ/mol (methacrylonitrile) to 35.7 kJ/mol (ethyl vinylether). As shown by good correlations with the alkene electron affinities (EA), log k298/M?1s?1 = 5.57 + 1.53 · EA/eV (R2 = 0.820) and Ea = 15.86 ? 7.38 · EA/eV (R2 = 0.773), hydroxymethyl is a nucleophilic radical, and its addition rates are strongly influenced by polar effects. No apparent correlation was found between Ea or log k298 with the overall reaction enthalpy. © 1995 John Wiley & Sons, Inc. 相似文献
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Villamena FA Merle JK Hadad CM Zweier JL 《The journal of physical chemistry. A》2007,111(39):9995-10001
Nitrones are potential synthetic antioxidants against the reduction of radical-mediated oxidative damage in cells and as analytical reagents for the identification of HO2* and other such transient species. In this work, the PCM/B3LYP/6-31+G(d,p)//B3LYP/6-31G(d) and PCM/mPW1K/6-31+G(d,p) density functional theory (DFT) methods were employed to predict the reactivity of HO2* with various functionalized nitrones as spin traps. The calculated second-order rate constants and free energies of reaction at both levels of theory were in the range of 100-103 M-1 s-1 and 1 to -12 kcal mol-1, respectively, and the rate constants for some nitrones are on the same order of magnitude as those observed experimentally. The trend in HO2* reactivity to nitrones could not be explained solely on the basis of the relationship of the theoretical positive charge densities on the nitronyl-C, with their respective ionization potentials, electron affinities, rate constants, or free energies of reaction. However, various modes of intramolecular H-bonding interaction were observed at the transition state (TS) structures of HO2* addition to nitrones. The presence of intramolecular H-bonding interactions in the transition states were predicted and may play a significant role toward a facile addition of HO2* to nitrones. In general, HO2* addition to ethoxycarbonyl- and spirolactam-substituted nitrones, as well as those nitrones without electron-withdrawing substituents, such as 5,5-dimethyl-pyrroline N-oxide (DMPO) and 5-spirocyclopentyl-pyrroline N-oxide (CPPO), are most preferred compared to the methylcarbamoyl-substituted nitrones. This study suggests that the use of specific spin traps for efficient trapping of HO2* could pave the way toward improved radical detection and antioxidant protection. 相似文献
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The rate constants for the reactions of OH radicals with fully fluorinated alkenes containing different numbers of -CF(3) groups next to olefinic carbon, CF(2)═CF(2), CF(2)═CFCF(3), CF(3)CF═CFCF(3), and (CF(3))(2)C═CFC(2)F(5), were measured between 230 and 480 K using the flash photolysis resonance fluorescence technique to give the following expressions: k(C(2)F(4))(250-480 K) = 1.32 × 10(-12) × (T/298 K)(0.9) × exp(+600 K/T) cm(3) molecule(-1) s(-1), k(C(3)F(6))(230-480 K) = 9.75 ×10(-14) × (T/298 K)(1.94) × exp(+922 K/T) cm(3) molecule(-1) s(-1), k(trans-C(4)F(8))(230-370 K) = 7.50 × 10(-14) × (T/298 K)(1.68) × exp(+612 K/T) cm(3) molecule(-1) s(-1), k(cis-C(4)F(8))(230-370 K) = 2.99 × 10(-14) × (T/298 K)(2.61) × exp(+760 K/T) cm(3) molecule(-1) s(-1), and k(C(6)F(12))(250-480 K) = 2.17 × 10(-15) × (T/298 K)(3.90) × exp(+1044 K/T) cm(3) molecule(-1) s(-1). The kinetics of the OH reaction in an industrial sample of octofluoro-2-propene (a mixture of the cis- and trans-isomers of CF(3)CF═CFCF(3)) was studied to determine the "effective" reaction rate constant for the typically industrial mixture: k()(230-480 K) = 7.89 × 10(-14) × (T/298 K)(1.71) × exp(+557 K/T) cm(3) molecule(-1) s(-1). On the basis of these results, the atmospheric lifetimes were estimated to be 1.2, 5.3, 21, 34, and 182 days for CF(2)═CF(2), CF(3)CF═CF(2), trans-CF(3)CF═CFCF(3), cis-CF(3)CF═CFCF(3), and (CF(3))(2)C═CFC(2)F(5), respectively. The general pattern of halolalkene reactivity toward OH is discussed. 相似文献
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Conclusions The rate constants for the addition of triethylsilyl radicals to -phenyl-N-tert-butylnitrone (kadd=(11±5)·106 liter/mole·sec) and 2,4,6-tri-tert-butylnitrosobenzene (kadd= (1.5±0.3)·109 liter/mole·sec) at 20°C were determined by the EPR method.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 938–941, April, 1984. 相似文献
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Leo Leung 《Journal of fluorine chemistry》2008,129(10):986-990
The AIBN-initiated addition of ethyl 4-iodo-2,2-difluoroacetate to a variety of alkene substrates is described. The addition generally led to the corresponding addition products in good to excellent yields and various functional groups could be tolerated under the reaction conditions. 相似文献
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It is shown how kinetic electron spin resonance spectroscopy with intermittent radical generation can be used to obtain rate constants of various simultaneous reactions in systems containing more than one kind of transient radicals. The technique is applied to reactions of tert-butyl [(CH3)3?] and isopropylol [(CH3)2?OH] radicals generated by photolysis of di-tert-butyl ketone and acetone in 2-propanol/acetone mixtures. It yields the rates of generation of the two radicals, the rate constants for their self- and crossterminations and for the reaction of tert-butyl with 2-propanol. The extent of diffusion control of the termination constants is discussed. 相似文献
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[reaction: see text] N-Aryl-5,5-diphenyl-4-pentenamidyl radicals (3) were produced by 266 nm laser-flash photolysis of the corresponding N-(phenylthio) derivatives, and the rate constants for the cyclizations of these radicals were measured directly. The 5-exo cyclization reactions were fast (k(c) > 2 x 10(5) s(-1)), and radicals 3 generally behaved as electrophilic reactants with a Hammett correlation of rho = 1.9 for five of the six radicals studied. However, the p-methoxyphenyl-substituted radical 3f cyclized much faster than expected from the Hammett analysis. Variable temperature studies of parent radical 3a (aryl = phenyl) gave an Arrhenius function with log k = 9.2 - 4.4/2.3RT (kcal/mol). The rate constant for the reaction of p-ethylphenyl-substituted anilidyl radical 3b with Bu(3)SnH at 65 degrees C was k(T) = 4 x 10(5) M(-1) s(-1). 相似文献
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The gas-phase reaction of ozone with eight 1,2-disubstituted alkenes has been investigated at ambient temperature (T = 286–296 K) and p = 1 atm. of air. The reaction rate constants, in units of 10−18 cm3 molecule−1s−1, are 144 ± 17 for cis-3-hexene, 157 ± 25 for trans-3-hexene, 89.8 ± 9.7 for cis-4-octene, 131 ± 15 for trans-4-octene, 114 ± 13 for cis-5-decene, ≥ 130 for trans-5-decene, 38.3 ± 5.0 for trans-2.5-dimethyl-3-hexene, and 40.3 ± 6.7 for trans-2.2-dimethyl-3-hexene. Substituent effects on alkene reactivity are examined. Cis-1,2-disubstituted alkenes are less reactive than the corresponding trans isomers. The 1,2-disubstituted alkenes that bear bulky substituents (substitution at the 3-carbon) are ca. 3 times less reactive than the corresponding n-alkyl substituted compounds. The atmospheric persistence of 1,2-disubstituted alkenes is briefly discussed. © 1996 John Wiley & Sons, Inc. 相似文献
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Rate constants were measured for the addition of the 2,4,6-tri(tert-butyl)phenoxyl radical (logk
10, [liter/(mole · sec)]) to the double bond of styrene (9.73 – 4621/T), methyl methacrylate (10.1 – 4972.7/T) and butylacrylate (7.68 – 4313.9/T); and for addition of the 2,4,6-tribromophenoxyl radical to styrene (k
10=0.5;T=323 K). A simulation based on these constants for the inhibited oxidation of styrene under conditions similar to those of monomer storage demonstrated the need to take account of this reaction when analyzing kinetic schemes describing the inhibited oxidation process.Institute of Nonaqueous Solution Chemistry, Russian Academy of Sciences, 150003 Ivanovo. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 12, pp. 2713–2718, December, 1992. 相似文献
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Iron-catalyzed sulfonyl radical formations from sulfonylhydrazides and oxidative addition to alkenes
Generation of sulfonyl radicals from sulfonylhydrazides has been achieved in the presence of a non-toxic iron catalyst and oxygen. The intermolecular addition of resultant sulfonyl radicals to alkenes affords β-hydroxysulfone compounds. 相似文献
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The rate constant for the bimolecular combination of benzyl radicals in cyclohexane and toluene is determined as a function of temperature. Further, it is studied in cyclohexane–toluene mixtures of different compositions. In the entire range covered, 9.8 × 108 ? 2kt ? 9.0 × 109M?1·sec?1, the data are very well described by the Smoluchowski equation for a diffusion-controlled reaction to ground-state products using a spin statistical factor of 1/4, a temperature- and solvent-independent reaction distance, and the known diffusion coefficient of toluene. 相似文献
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Georgia Nicolaou 《Tetrahedron letters》2008,49(44):6324-6326
N-Phenyltriazolinedione is found to be an efficient initiator in the radical (anti-Markovnikov) addition of thiophenol to 2-methyl-2-butene. A second, minor, product (an alcohol, from oxygen addition) was also obtained, and a possible mechanistic scheme is proposed. 相似文献
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《Tetrahedron letters》1999,40(40):7285-7288
The addition of toluenesulfonyl radicals to solid-supported alkenes and alkynes gives bromo-sulfonyl alkenes and alkanes in good yields. 相似文献
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Laser flash photolysis (at 248 or 308 nm) or aryl iodides in water or water/methanol solutions produces iodine atoms and phenyl radicals. Iodine atoms react rapidly with added I? to form I2? but do not react rapidly with O2 (k ? 107 L mol?1 s?1). Iodine atoms oxidize phenols to phenoxyl radicals, with rate constants that vary from 1.6 × 107 L mol?1 s?1 for phenol to about 6 × 109 L mol?1 s?1 for 4-methoxyphenol and hydroquinone. Ascorbate and a Vitamin E analogue are also oxidized very rapidly. N-Methylindole is oxidized by I atoms to its radical cation with a diffusion-controlled rate constant, 1.9 × 1010 L mol?1 s?1. Iodine atoms also oxidize sulfite and ferrocyanide ions rapidly but do not add to double bonds. The phenyl radicals, produced along with the I atoms, react with O2 to give phenylperoxyl radicals, which react with phenols much more slowly than I atoms. © 1995 John Wiley & Sons, Inc. 相似文献
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Products of the radical reactions arising from t-Bu2O2, CF3I, and CH3I at 146°C in the vapor phase have been measured over a 33-fold range of CH3I/CH3I ratios and shown to be governed by the rapidly established equilibrium Together with K estimated by thermochemical methods, the results yield, for the rate of recombination for CF3· radicals, kr = 109.7 ± 0.5 M?1 sec?1. 相似文献