共查询到20条相似文献,搜索用时 15 毫秒
1.
Yasuro Hori Shigetaka Shimada Hisatsugu Kashiwabara 《Journal of Polymer Science.Polymer Physics》1984,22(8):1407-1415
The decay of peroxy radicals trapped in irradiated isotactic polypropylene has been studied by ESR in air at various temperatures between 284 and 309 K. All the ESR spectra obtained at the various reaction stages are shown to be composed of two components arising from a mobile fraction and an immobile fraction. Only the mobile peroxy radicals decay; those belonging to the immobile fraction are stable. Various reaction mechanisms are examined in order to explain the experimental results; it is concluded that the decay reaction is controlled by diffusion of peroxy radicals and that the immobile peroxy radicals play no role in the decay reaction. Intermolecular hydrogen abstraction of the peroxy radicals, rather than intramolecular abstraction, is suggested as the rate-determining reaction. 相似文献
2.
Polyamide 6 has been mechanically destructed in vacuo. At -70°, the ESR spectrum corresponds to the sum of the component spectra of three radicals NH?HCH2, ·CH2NHCO, and ·CH2CONH. After introducing air into the ampoule, the spectrum changes even at -70°; the changes have been studied up to 0°. The spectrum of the peroxy radical ROO· (with line width 1.57 mT, g1 = 2.0089 and g| = 2.0301) predominates. 相似文献
3.
4.
The ESR spectra of peroxy radicals in irradiated powders and oriented samples of polytetrafluoroethylene (PTEE) have been measured with a K-band spectrometer, and the principal values and directions of the g tensor were determined both at room temperature and at 77°K. In contrast to the spectra of the usual peroxy radicals, those trapped in γ-irradiated PTFE exhibited an ESR spectrum apparently having a larger principal value for g⊥ than for g∥ when measured at room temperature, although the normal principal values were observed at 77°K. As for the directions of the principal axes, g∥ was directed along the chain axis at room temperature and was perpendicular to the chain axis at 77°K. From the temperature change of the g tensor and the line shapes in the oriented samples, it is shown that the observed temperature change of the spectra is due to rapid rotation at room temperature around the chain axis rather than around the C? O bond axis. Assuming this, the apparent principal values of the g tensor at room temperature were calculated from the g tensor obtained at 77°K. for the rigid state, and the results are in good agreement with observations at room temperature. A structure for the peroxy radicals is also proposed. In addition, the spectral line shape function for the uniaxially oriented samples has been derived. 相似文献
5.
Masahiro Kikuchi Mohammad S. Hussain Norio Morishita Mitsuko Ukai Yasuhiko Kobayashi Yuhei Shimoyama 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2010,75(1):310-313
An electron spin resonance (ESR) spectroscopic study of radicals induced in irradiated fresh mangoes was performed. Mangoes in the fresh state were irradiated with γ-rays, lyophilized and then crushed into a powder. The ESR spectrum of the powder showed a strong main peak at g = 2.004 and a pair of peaks centered at the main peak. The main peak was detected from both flesh and skin specimens. This peak height gradually decreased during storage following irradiation. On the other hand, the side peaks showed a well-defined dose–response relationship even at 9 days post-irradiation. The side peaks therefore provide a useful means to define the irradiation of fresh mangoes. 相似文献
6.
A. V. Il'yasov V. I. Morozov A. A. Vafina V. A. Naumov 《Russian Chemical Bulletin》1991,40(7):1335-1338
Iminoxyl radicals involved in the homolytic oxidation of nitrolic acids, with the general formula (NO2)RC=NO., have been detected by means of ESR. In the presence of a strong acid, the ESR spectra of the radical (NO2)2C=NO. exhibits alternation of the line widths, owing to syn-anti isomerization.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1513–1516, July, 1991. 相似文献
7.
Mingqiang Huang Zhenya Wang Yong Yang Liqing Hao Wenwu Zhao Xiaoming Gao Li Fang Weijun Zhang 《International journal of quantum chemistry》2007,107(5):1092-1098
The hydroxycyclohexadienyl peroxy radicals (HO? C6H6? O2) produced from the reaction of OH‐benzene adduct with O2 were studied with density functional theory (DFT) calculations to determine their characteristics. The optimized geometries, vibrational frequencies, and total energies of 2‐hydroxycyclohexadienyl peroxy radical IIs and 4‐hydroxycyclohexadienyl peroxy radical IIIs were calculated at the following theoretical levels, B3LYP/6‐31G(d), B3LYP/6‐311G(d,p), and B3LYP/6‐311+G(d,p). Both were shown to contain a red‐shifted intramolecular hydrogen bond (O? H … O? H bond). According to atoms‐in‐molecules (AIM) analysis, the intramolecular hydrogen bond in the 2‐hydroxycyclohexadienyl peroxy radical IIs is stronger than that one in 4‐hydroxycyclohexadienyl peroxy radical IIIs, and the former is the most stable conformation among its isomers. Generally speaking, hydrogen bonding in these radicals plays an important role to make them more stable. Based on natural bond orbital (NBO) analysis, the stabilization energy between orbitals is the main factor to produce red‐shifted intramolecular hydrogen bond within these peroxy radicals. The hyperconjugative interactions can promote the transfer of some electron density to the O? H antibonding orbital, while the increased electron density in the O? H antibonding orbital leads to the elongation of the O? H bond and the red shift of the O? H stretching frequency. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
8.
This review deals with the most fundamental fluorocarbon oxy (x=1) and peroxy (x=2) radicals CF3Ox, FC(O)Ox, CF3C(O)Ox and CF3OC(O)Ox. Their role in atmospheric and synthetic chemistry is described as well as their formation and characterisation in the gas phase and isolated in low temperature matrices. Reservoirs and hence thermal sources for oxy and peroxy radicals are peroxides (ROOR) and peroxynitrates (ROONO2), while catenated trioxides (ROOOR) are precursors for both oxy and peroxy radicals simultaneously. The synthesis and some properties of these precursors are also described. 相似文献
9.
The possibility of combined application of ESR and dielectric relaxation methods in determining the character of molecular rotation of organic nitroxyl radicals in nonpolar liquids is studied for solutions of 2,2,6,6-tetramethyl-piperidine-N-oxide in decaline. Comparison of the two correlation times for rapid radical rotation obtained by both methods provides evidence for an essentially jump-like rotation of this radical. 相似文献
10.
B. L. Tumansky V. N. Lebedev N. N. Bubnov S. P. Solodovnikov L. L. Gervits E. V. Balagurova L. I. Zakharkin 《Russian Chemical Bulletin》1993,42(7):1259-1261
It has been shown by ESR that the addition of photochemically generated boroncentered carboranyl radicals to branched fluoroalkenes affords stable spin-adducts. It has been found that the addition of boron-centered radicals with 1-substituted 2-fluoroalkenyl-o-carborane gives stable -carboranyl radicals. Negligible variations in the values of the constants of hyperfine coupling of the unpaired electron with the nucleus of the -11B atom in radicals of various structures imply the stability of the carborane conformation with respect to the 2p
z-orbital of the unpaired electron. This may be caused by hyperconjugation between the boron atom and the unpaired electron as well as steric interaction.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1316–1318, July, 1993. 相似文献
11.
Methyl and ethyl derivatives of thiobenzothiazole and their quaternary salts were prepared by the sealed glass tube method. Azinodibenzothiazoles were oxidized by lead(IV) acetate, giving cation radical salts with the boron tetrafluoride anion moiety. The well-resolved esr spectra observed were analyzed by comparing the data with those of a deuteriomethylated radical and with those from the MO calculations. Spin density distribution was consistently determined by computer simulation, including almost the same unpaired electron distribution on the four nitrogen atoms. 相似文献
12.
B. L. Tumanskii V. V. Bashilov N. N. Bubnov S. P. Solodovnikov V. I. Sokolov 《Russian Chemical Bulletin》1992,41(8):1519-1520
A. N. Nesmeyanov Institute of Organometallic Compounds, Russian Academy of Sciences, 117813 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 8, pp. 1936–1937, August, 1992. 相似文献
13.
S. L. Khursan V. S. Martemianov R. L. Safiullin N. S. Baisheva G. S. Ismagilova 《Reaction Kinetics and Catalysis Letters》1987,34(2):427-432
Termination rate constants of peroxy radicals of seven polyatomic esters in benzene and perflouorooctane media have been measured by pulse photolysis. Recombination of peroxy radicals for all esters examined proves to be diffusion controlled. Reactivity of peroxy radicals in the termination reaction grows with increasing number of ester groups.
. . .相似文献
14.
Z. A. Mansurov D. U. Bodikov G. I. Ksandopulo 《Reaction Kinetics and Catalysis Letters》1988,37(1):31-35
Stabilized hexane-air cool flames in a separately heated two-section reactor have been studied at T=480–770 K and P=30–63 kPa. ESR spectra of peroxy radicals were analyzed by the radical freezing technique and sonde sampling. Under these conditions high radical concentrations (>1014 cm–3) are observed. With increasing pressure and temperature, the fraction of HO2 radicals in the overall amount of radicals grows.
480–770 , 30–63 . . , (>1014cm–3). , HO2 .相似文献
15.
Matni A Boubekeur L Grosshans P Mézailles N Bernardinelli G Le Floch P Geoffroy M 《Magnetic resonance in chemistry : MRC》2007,45(12):1011-1017
Bis-iminophosphoranes containing various types of linkers between two R3P==N moieties were electrochemically oxidized at controlled potential in situ in the electron spin resonance (ESR) cavity. For linkers constituted of phenylenes, conjugated phenylenes or merely a dicyanoethylenic bond, this oxidation led to well-resolved ESR spectra which were characterized by their g values and by their 1H, 14N and 31P isotropic hyperfine constants. These coupling constants agree with those calculated by DFT for the corresponding cation radicals. Experimental and theoretical results clearly indicate that in these species the unpaired electron is mostly delocalized on the bridge and on the nitrogen atoms while the spin density on the phosphorus atoms is particularly small. Cyclic voltammetry and ESR spectra show that the nature of the bridge between the two iminophosphoranes considerably influences the oxidation potential of the compound as well as the stability of the radical cation. Information about the conformation of the precursor containing two Ph3P==N moieties separated by a --C(CN)==C(CN)--group was obtained from its crystal structure. 相似文献
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17.
L. A. Davis C. A. Pampillo T. C. Chiang 《Journal of Polymer Science.Polymer Physics》1973,11(5):841-854
The rate of peroxy radical accumulation as a function of strain at various temperatures in AC1220 high molecular weight polyethylene has been determined by EPR spectroscopy. The results of isothermal radical decay experiments are used, where appropriate, to correct the apparent accumulation rate to the actual rate. An exponential dependence of radical concentration [R], on true strain is observed at all temperatures investigated in the range from 160 to 294°K. For constant effective strain, measured from the approximate strain at which radical accumulation initiates, it is found that d[R]/de exhibits two sharp transitions as a function of temperature. One of these, at low temperature, is believed to be associated with the glass transition of the amorphous phase of the material; the other, at higher temperature, is believed to occur as a result of a change in the rate-controlling mechanism of deformation. 相似文献
18.
The kinetics of 1,1-dimethylpropyl peroxy radicals recombination in polar solvents—water, methanol, and their mixtures—was studied by EPR spectroscopy in combination with the stopped-flow method, and the rate constants of this reaction were determined. Peroxyl radicals were generated by mixing solutions of Ce4+ sulfate and 1,1-dimethylpropyl hydroperoxide. The observed EPR signal of the peroxyl radical is a singlet with a g-factor of 2.015 ± 0.001, and a line width of ΔH = (1.36 ± 0.02) × 10?3 T for methanol and ΔH = (9.7 ± 0.2) × 10?4 T for water. The measured rate constants of (CH3)2C(O2·)CH2CH3 radical recombination at 298 K are 2kt = (3.9 ± 0.4) × 104 L mol?1 s?1 for water and 2kt = (5.2 ± 0.5) × 103 L mol?1 s?1 for methanol. A linear relationship between ln(2kt) and the Kirkwood function (ε?1)/(2ε + 1), where e is the dielectric constant of the medium, has been established, indicating an important role of nonspecific solvation in the recombination of tertiary peroxyl radicals. 相似文献
19.
A chain mechanism is proposed to account for the very rapid termination reactions observed between alkyl peroxy radicals containing α-C—H bonds which are from 104 to 106 faster than the termination of tertiary alkyl peroxy radicals. The new mechanism is with termination by . \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm R}\overline {{\rm CHOO}} $\end{document} is the zwitterion originally postulated by Criegee to account for the chemistry of O3-olefin addition. Heats of formation are estimated for \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {{\rm CH}_2 {\rm OO,}} {\rm }\overline {{\rm RCHOO}} $\end{document}, and \documentclass{article}\pagestyle{empty}\begin{document}$ ({\rm C}\overline {{\rm H}_3 )_2 {\rm COO}} $\end{document} and it is shown that all steps in the mechanism are exothermic. The second step can account for (1Δ)O2 which has been observed. k1 is estimated to be 109–2/θ liter/M sec where θ = 2.303RT in kcal/mole. The second and third steps constitute a chain termination process where chain length is estimated at from 2 to 10. This mechanism for the first time accounts for minor products such as acid and ROOH found in termination reactions. Trioxide (step 3) is shown to be important below 30°C or in very short time observations (<10 s at 30°C). Solvent effects are also shown to be compatible with the new mechanism. 相似文献
20.
The effect of 1,1,1,3,3,3-hexafluoro-2-phenylpropan-2-ol (HFPP) on the persistency of sec-alkyl peroxy radicals has been investigated. The formation of a hydrogen-bonding complex between HFPP and the radical resulted in a large increase in the lifetime of the radical. This variation was accompanied by a decrease in the g-value. An enthalpy change of -3.4 kcal mol-1 was estimated for the formation of the hydrogen-bonded complex. 相似文献