Spin Trapping of the Phosphorus-centered Radicals Generated from Hydrogen Abstraction Reaction by 2,2-Diphenyl-1-picrylhydrazyl

IntroductionSPin trapping technique has been widely used for the detection and identification of unstable radicals. As traps, nitrones and nitroso compounds are most widely usedll--4]. However,the identification of spin adducts by EPR spectroscopy is rather difficult because the variationof the hyperfine coupling constants(hfccs) of spin adducts caused by the structural changes oftrapped radicals is not very large. Recently, the ph osp horns- con t al m ng m t rox id e h a s att ra ctedmuch …     

Studying the Fundamentals of Radical Polymerization Using ESR in Combination with Controlled Radical Polymerization Methods

Electron spin resonance (ESR) spectroscopy can contribute to understanding both the kinetics and mechanism of radical polymerizations. A series of oligo/poly(meth)acrylates were prepared by atom transfer radical polymerization (ATRP) and purified to provide well defined radical precursors. Model radicals, with given chain lengths, were generated by reaction of the terminal halogens with an organotin compound and the radicals were observed by ESR spectroscopy. This combination of ESR with ATRPs ability to prepare well defined radical precursors provided significant new information on the properties of radicals in radical polymerizations. ESR spectra of the model radicals generated from tert-butyl methacrylate precursors, with various chain lengths, showed clear chain length dependent changes and a possibility of differentiating between the chain lengths of observed propagating radicals by ESR. The ESR spectrum of each dimeric, trimeric, tetrameric, and pentameric tert-butyl acrylate model radicals, observed at various temperatures, provided clear experimental evidence of a 1,5-hydrogen shift.     

Radical Intermediates in the Decomposition of Substituted Coumarins

Summary. A series of coumarin derivatives containing substituents with an acidic CH₂ group in 3-position was decomposed on the surface of PbO₂. The radical intermediates were identified by EPR spectroscopy. Although the occurrence of several tautomeric forms is possible, the application of the spin trapping technique confirmed the formation of only one radical product, namely the C-radical resulting from the homolytic splitting of the C–H bond of the methylene group.     

Radical intermediates in the photorearrangement of 3-hydroxyindolic nitrones

A number of 3-hydroxy substituted indolic nitrones were found to quantitatively photorearrange to (2-benzoylamino)phenyl ketones upon UV-A irradiation. EPR-Spin Trapping experiments suggest that the process, which is believed to proceed via the formation of an oxaziridine, follows a homolytic pathway. Although DFT calculations do not allow to totally exclude alternative routes involving singlet intermediates, they do provide support to the proposed homolytic mechanism, which would be driven by a 1,5-hydrogen transfer subsequent to the oxaziridine ring opening. When this hydrogen transfer was made impossible by methylation of the 3-OH group, a benzoxazine was isolated as the sole reaction product.     

SO·4-自由基氧化酪氨酸反应中的溶剂效应

研究了水-乙腈混合溶液中SO·4-自由基氧化酪氨酸的反应.实验结果表明,SO·4-自由基氧化酪氨酸的反应机制不因乙腈的加入而改变,但所产生的瞬态粒子的动力学行为受到较大影响.随介质中乙腈体积分数的增加,SO·4-的衰变速率减慢而酪氨酸中性自由基(TyrO·)的衰变速率加快.我们认为这两种自由基所呈现出来的相反的溶剂效应是由于其所带电荷的不同.随介质中乙腈体积分数的增加,SO·4-氧化酪氨酸的反应速率减慢.这一实验结果意味着,在有机溶剂存在的情况下TyrO·/TyrOH的氧化还原电势可能发生了变化,从而旁证了关于TyrO·/TyrOH的氧化还原电势因酪氨酸从游离状态变到肽或蛋白质中而发生变化的推测.     

掺硼金刚石膜电极表面产生羟基自由基的原位ESR研究

建立了原位电化学-电子顺磁共振(ESR)方法,系统研究了掺硼金刚石(BDD)膜电极表面在水溶液中的羟基自由基(·OH)产生规律.结果表明,在高于析氧电位时,·OH的生成速率随着阳极电位的升高、电流密度的增加而增大,增加速率逐渐减缓.与此同时,与氢终端的BDD膜电极相比,氧终端的BDD膜电极表面因具有较好的亲水性而具有更高的·OH产生能力.在电化学氧化处理有机废水的过程中,电极表面处于氧终端的状态,有利于·OH产生并保持较高的活性.溶液pH值也在一定程度上影响·OH生成反应,酸性溶液中,BDD膜电极表面的·OH产生能力强于在中性或碱性溶液中.进一步研究发现,BDD膜电极表面还可能生成O3-·0自由基.本研究为深入探索BDD膜电极表面·OH的产生机制提供了研究手段,为阐述BDD膜电极电极在污染物处理中高效性的本质提供了有效的证据.     

ESR study of the 1,2-migration of F atoms in polyfluorinated radicals

The 1,2-migration of the F atom in polyfluorinated cyclohexadienyl radicals generated in the reaction of perfluoro-p-xylene with pentafluorobenzoyl peroxide has been observed directly by ESR.Translated fromIzvestiya Akademii Nauk. Seriya Khitnicheskaya, No. 1, pp. 100–103, January, 1995.     

Addition of 1,2- and 1,3-Dithiols to 2-alkoxypropenals - a New Method for the Production of Substituted Dithiacycloalkanes

The reaction of 2-alkoxypropenals with ethane-1,2-dithiols and propane-1,3-dithiols under various conditions was studied by ¹H NMR and chromato-mass spectrometry. Under kinetically controlled conditions at 20° in the absence of catalysts the addition of dithiols takes place according to the Markovnikov rule. The primary adducts are unstable and are quickly converted into the corresponding substituted 1,4-dithiacycloheptane or 1,4-dithiane. The latter in turn can be converted under the reaction conditions or at high temperature into a thiolane derivative. The reaction of 2-ethoxypropenal with a twofold excess of ethane-1,2-dithiol at 60°C in the presence of p-toluenesulfonic acid leads to 2-methyl-2,2'-bi(dithiolane)     

Controlled radical polymerization of styrene in the presence of cyclic 1,2‐disulfides

The thermal polymerization of styrene (St) in the presence of cyclic 1,2‐disulfides at 120 °C was investigated. In the polymerization of St in the presence of 1,2‐dithiane (DT), that is, six‐member cyclic 1,2‐disulfide, the polymer yields and molecular weights increased with the reaction time. The linear relation between the polymer yields and molecular weights was observed, and the line passed through an original point. The molecular weight distributions of the polymers remained almost constant but were not narrow. For this polymerization with a living nature, we proposed the following mechanism: the propagating St radical reacted with thiyl radicals derived from DT, leading to the formation of dormant species, and the formed C S bond of the dormant was dissociated again to give the propagating polystyryl radical and thiyl radical. Similar results were obtained in the thermal polymerization of St at 120 °C in the presence of 1,2‐dithiacycloheptane, that is, seven‐member cyclic 1,2‐disulfide. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 145–151, 2001     

Study of the Dependence on Temperature and Composition of the Volumic Properties of Ethane-1,2-diol + 2-Methoxyethanol + 1,2-Dimethoxyethane + Water Solvent System and Graphical Representation in the Quaternary Domain

In this paper, the temperature and composition dependencies of the volumetric behavior are studied for the ethane-1,2-diol + 2-methoxyethanol + 1,2-dimethoxyethane + water quaternary system. Density data were collected at different temperatures ranging from −10 to 80 ^∘C and at atmospheric pressure over the whole composition range, 0≤ x_i(i = 1, 2, 3, 4)≤ 1. Moreover, we also made use of the results on the six binary (ij) and four ternary (kij) subsystems studied previously. The excess molar volume (V^E) data have been fitted to an equation derived from the well-known Redlich–Kister equation and some interesting correlations were found. Furthermore, in order to represent in an effective way the behavior of the V^E = V^E(x_i) function (and of the derived partial molar quantities) in the quaternary domain, a new algorithm has been developed, which gives 3D plots where the dependent function is depicted by means of “colored slices” of the tetrahedron corresponding to the investigated composition quaternary domain.     

磁场对光催化反应羟基自由基生成速率的影响

以对苯二酸作为Pt/TiO₂光催化反应所产生的羟基自由基(•OH)的捕获剂, 采用荧光技术考察外加磁场对羟基自由基(•OH)生成速率的影响, 结果表明, 与常规的光催化反应相比, 外加磁场可使样品表面羟基自由基的生成速率提高11.7%.     

Solvent effects in the fluorination of 1,2-dichloro-1,1-difluoroethane (R-132b) to 2-chloro-1,1,1-trifluoroethane (R-133a)

Trichloroethylene has been found to act as a rate enhancing co-factor in the liquid phase, tantalum (V) halide catalyzed, fluorine-for-chlorine exchange reaction of 1,2-dichloro-1,1-difluoroethane (R-132b) to 2-chloro-1,1,1-trifluorethane (R-133a). Several trifluoromethyl substituted benzenes have also been found to be rate-enhancing solvents.     

用电子顺磁共振法定量检测极性溶剂中的低浓度自由基

本文以定量检测甲基丙烯酸甲酯(MMA)本体聚合反应过程中的增长自由基为例,介绍了如何用电子顺磁共振(EPR)方法定量检测极性溶剂中的低浓度自由基。详细地介绍了用自制的扁平样品池有效地克服了极性溶剂的非共振吸收现象,用计算机减谱的方法扣除了比信号大很多的背景信号。     

SP‐PLP‐EPR—A Novel Method for Detailed Studies into the Termination Kinetics of Radical Polymerization

Single pulse–pulsed laser polymerization–electron paramagnetic resonance (SP‐PLP‐EPR) has been introduced as a powerful method for the very detailed analysis of termination kinetics. During polymerization an intense laser pulse is applied in order to almost instantaneously produce a burst of radicals. The decay of radical concentration is measured by highly time‐resolved EPR and is analyzed with respect to the rate coefficients for the termination of two radicals of identical size. SP‐PLP‐EPR experiments have been carried out for an itaconate monomer, for several methacrylates in bulk and in a solution of ionic liquids, for methacrylic acid in aqueous solution, and for the solution polymerization of butyl acrylate in toluene at low temperature. The data fully support the composite model, which assumes a stronger chain‐length dependence of termination for radicals of smaller size and a weaker one for large radicals. The SP‐PLP‐EPR technique is also applicable in systems with more than one type of growing radicals, as is the case with butyl acrylate polymerization at higher temperature and with RAFT polymerizations, where the novel method may be used for a comprehensive kinetic analysis.

     

Reactivity of the carbocation generated in the photolysis of 1,2,2,4,6-pentamethyl-1,2-dihydroquinoline toward azide ion

The reaction of the azide ion with the carbocation generated in the photolysis of 1,2,2,4,6-pentamethyl-1,2-dihydroquinoline in methanol was studied by pulse (conventional and laser) and steady-state photolysis techniques. The adduct of the azide ion was characterized by ¹H NMR spectrum. Experimental results were interpreted taking into account a competition between the addition of methanol and azide ion to the carbocation. The rate constants for the reaction of the azide ion with the carbocation (k _Az) were measured at 2—48 °C in a wide range of [N₃ ^–]₀ concentrations from 2·10^–7 to 0.1 mol L^–1 at different ionic strengths () of the solution. The resulting k _Az values are more than an order of magnitude lower than those for diffusional-controlled reactions and vary from 3.2·10⁸ ( = 0) to 4.5·10⁶ L mol^–1 s^–1 ( = 0.8 mol L^–1) in the presence of NaClO₄ (18 °C). The activation energy of addition of the azide ion to the carbocation is 21 kJ mol^–1, which is by 12 kJ mol^–1 lower than the activation energy of the reaction of the carbocation with methanol. The features of the reaction under study are discussed from the viewpoint of the structures of carbocations generated in the photolysis of dihydroquinolines.     

Crystal Structure and Magnetic Property of 2-(Imidazo[1,2-a]pyri-din-2-yl)-2-oxoacetic Acid and Its Perchlorate

We herein report two crystals based on 2-(imidazo[1,2-a]pyridin-2-yl)-2-oxoacetic acid radical and its perchlorate, and investigate the relationship between magnetic properties and crystal stacking structures or supramolecular interactions. 2-(Imidazo[1,2-a]pyridin-2-yl)-2-oxoacetic acid radical in two crystals mainly exist as diamagnetic dimer formed via short atomic contacts or supramolecular interactions (hydrogen bonds, anion-π or lonepair-π interactions), leading to low magnetic susceptibilities. 2-(Imidazo[1,2-a]pyridin-2-yl)-2-oxoacetic acid radical crystal exhibits quasi-one-dimensional columnar stacking chain and weak antiferromagnetism. However, its perchlorate crystal possesses one-dimensional doublestranded chain structure assembled through double hydrogen bonds and anion-π interactions, and reveals weak ferromagnetism.     

Topological approach in determining the structure-property dependence in a series of 4-cyclohexene-1,2-dicarboxylic acids

Theoretical information indices of cis- and trans-4-cyclohexene-1,2-dicarboxylic acids and their methyl and dimethyl substituted derivatives are calculated. Correlations between the indices and physicochemical properties of these compounds are analyzed. Original Russian Text Copyright ? 2009 by M. S. Salakhov, B. T. Bagmanov, and O. T. Grechkina __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 50, No. 1, pp. 183–187, January–February, 2009.