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杯芳烃与NO2硝化反应的研究 总被引:1,自引:0,他引:1
系统地研究了羟基杯[n]芳烃、甲氧基杯[n]芳烃和对特丁基杯[n]芳烃(n=4, 6, 8)与NO2气体的硝化反应, 发现可以成功地得到25,26,27,28-四羟基杯[4]芳烃、37,38,39,40,41,42-六羟基杯[6]芳烃以及25,26,27,28-四甲氧基杯[4]芳烃的对位全硝化产物, 产率分别为90%, 70%和40%; 尤其是25,26,27,28-四羟基杯[4]芳烃与NO2的反应20 min即可完成. 认为共振式酚氧负离子结构是影响该类硝化反应的关键, 并对反应机理进行了探讨. 相似文献
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原子尺度锂离子电池电极材料的近平衡结构 总被引:1,自引:0,他引:1
锂离子电池充放电过程中电极材料的结构变化与材料的电化学反应机理和性能密切相关.通过在原子尺度上直接观察脱/嵌锂前后电极材料的近平衡微观结构,有助于从更深层次认识电极反应机理和性能演化规律,对于全面理解材料的电化学行为以及改善锂离子电池性能具有重要的指导意义.本文详述了球差校正扫描透射成像技术在研究电极材料表界面结构及反应机理方面的进展,探讨了未来建立电极材料原子尺度结构与性能相关联可能的研究方向. 相似文献
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借助付里叶红外光谱、X-射线衍射以及电子显微技术,结合化学提纯方法,检测纤维素分子中主要基团、分子取向度和超分子结构形态等方面的变化,考察了均相条件下硝化纤维素与甲基丙烯酸甲酯接枝共聚物的形成与发生接枝共聚反应的部位,探索均相接枝的可能反应机理。 相似文献
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在电化学界面,电催化过程通常包括电子转移、吸附和脱附、静电相互作用、溶剂化及去溶剂化等多步过程,深入理解电催化反应机理极具挑战性.对纳米结构电化学界面(电极)处电催化过程的深入理解十分有助于阐明电催化反应机理和设计高性能电催化剂材料.电催化活性通常与电催化剂表面局域化的活性位点密切有关.在反应条件下,电催化反应过程的研究极大依赖于高分辨表征技术.经典的宏观电化学表征方法仅可以提供不同界面位点的平均信息,很难分辨一些特殊结构位点(如缺陷、晶界、边缘位点)的相关重要电化学信息.原位电化学扫描探针显微镜技术,包括电化学扫描隧道显微镜(EC-STM)、电化学原子力显微镜(EC-AFM)、扫描电化学显微镜(SECM)及扫描电化学池显微镜(SECCM),能够在纳米及原子尺度研究电催化反应过程,弥补了宏观表征方法的不足,为探究构效关系和解析电催化反应机理提供了机遇.本文介绍了各种扫描显微技术的基本原理、特点及优劣势,并且概述了各项技术在电催化领域研究的重大进展.EC-STM和EC-AFM能够原位表征电催化过程中的纳米尺度表面结构演变及吸附/脱附过程,但无法直接测量局部电化学活性(法拉第电流).通过S... 相似文献
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Tanaka M Muro E Ando H Xu Q Fujiwara M Souma Y Yamaguchi Y 《The Journal of organic chemistry》2000,65(10):2972-2978
The nitration of methylnaphthalenes with NO(2)BF(4) and NOBF(4) was examined in order to shed light on the controversial aromatic nitration mechanism, electrophilic vs charge-transfer process. The NO(2)(+) nitration of 1,8-dimethylnaphthalene showed a drastic regioselectivity change depending on the reaction temperature, where ortho-regioselectivity at -78 degrees C and para-regioselectivity at 0 degrees C were considered to reflect the electrophilic and the direct or alternative charge-transfer process, respectively, because the NO(+) nitration through the same reaction intermediates as in the NO(2)(+) nitration via a charge-transfer process resulted in para-regioselectivity regardless of the reaction temperature. The NO(2)(+) nitration of redox potential methylnaphthalenes higher than 1,8-dimethylnaphthalene gave a similar ortho-regioselectivity enhancement to 1,8-dimethylnaphthalene at lower temperature, thus reflecting the electrophilic process. On the other hand, the NO(2)(+) nitration of redox potential methylnaphthalenes lower than 1,8-dimethylnaphthalene showed para-regioselectivity similar to the NO(+) nitration, indicating the direct or alternative charge-transfer process. In the presence of strong acids where the direct charge-transfer process will be suppressed by protonation, the ortho-regioselectivity enhancement was observed in the NO(2)(+) nitration of 1,8-dimethylnaphthalene, suggesting that the direct charge-transfer process could be the main process to show para-regioselectivity. These experimental results imply that the NO(2)(+) nitration proceeds via not only electrophilic but also direct charge-transfer processes, which has been considered to be unlikely because of the high energy demanding process of a bond coordination change between NO(2)(+) and NO(2). Theoretical studies at the MP2/6-31G(d) level predicted ortho- and para-regioselectivity for the NO(2)(+) nitration via electrophilic and charge-transfer processes, respectively, and the preference of the direct charge-transfer process over the alternative one, which support the experimental conclusion 相似文献
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Gwaltney SR Rosokha SV Head-Gordon M Kochi JK 《Journal of the American Chemical Society》2003,125(11):3273-3283
The highly disparate rates of aromatic nitrosation and nitration, despite the very similar (electrophilic) properties of the active species: NO(+) and NO(2)(+) in Chart 1, are quantitatively reconciled. First, the thorough mappings of the potential-energy surfaces by high level (ab initio) molecular-orbital methodologies involving extensive coupled-cluster CCSD(T)/6-31G optimizations establish the intervention of two reactive intermediates in nitration (Figure 8) but only one in nitrosation (Figure 7). Second, the same distinctive topologies involving double and single potential-energy minima (Figures 6 and 5) also emerge from the semiquantitative application of the Marcus-Hush theory to the transient spectral data. Such a striking convergence from quite different theoretical approaches indicates that the molecular-orbital and Marcus-Hush (potential-energy) surfaces are conceptually interchangeable. In the resultant charge-transfer mechanism, the bimolecular interactions of arene donors with both NO(+) and NO(2)(+) spontaneously lead (barrierless) to pi-complexes in which electron transfer is concurrent with complexation. Such a pi-complex in nitration is rapidly converted to the sigma-complex, whereas this Wheland adduct in nitrosation merely represents a high energy (transition-state) structure. Marcus-Hush analysis thus demonstrates how the strongly differentiated (arene) reactivities toward NO(+) and NO(2)(+) can actually be exploited in the quantitative development of a single coherent (electron-transfer) mechanism for both aromatic nitrosation and nitration. 相似文献
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Patel A Liebner F Netscher T Mereiter K Rosenau T 《The Journal of organic chemistry》2007,72(17):6504-6512
In contrast to the alpha-form permethylated at the aromatic ring, non-alpha-tocopherols possess free aromatic ring positions which enable them to act as potent scavengers of electrophiles in vivo and in vitro. In preparation of enzymatic studies involving peroxynitrite and other nitrating systems, the behavior of non-alpha-tocopherols under nitration conditions was studied. The nitration products of beta-, gamma-, and delta-tocopherol were identified, comprehensively analytically characterized, and their structure was supported by X-ray crystal structure analysis on truncated model compounds. Even under more drastic nitration conditions, no erosion of the stereochemistry at 2-C occurred. The nitrosation of gamma-tocopherol and delta-tocopherol was re-examined, showing the slow oxidation of the initial nitroso products to the corresponding nitro derivatives by air to be superimposed by a fast equilibrium with the tautomeric ortho-quinone monoxime, which only in the case of gamma-tocopherol released hydroxyl amine at elevated temperatures to afford the stable ortho-quinone. Mononitration of delta-tocopherol selectively proceeded at position 5. This selectivity can be explained by the theory of strain-induced bond localization (SIBL) to the quinoid nitration intermediates. Bisnitration was only insignificantly disfavored by the first nitro group, so that under normal nitration conditions offering an excess of nitrating species only the bisnitration product was found. 相似文献
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In this work we have examined the nitration by acetyl nitrate of a range of activated and deactivated aromatic substrates in two ionic liquids and compared the results to the same reaction in dichloromethane. Both ionic liquids are stable to the reaction conditions, and in both ionic liquids the yields of reaction are higher after unit time than the same reactions in dichloromethane, although the regioselectivity is little affected by solvent choice. This result gives further support to the suggestion that in the ionic liquid, acetyl nitrate dissociates to give the nitronium ion, and that this is the effective nitrating agent here. However, it is shown that [bmpy][N(Tf)(2)] is a better solvent for aromatic nitration than [bmpy][OTf]. This is due to the ease of formation of nitronium ion in the former ionic liquid, and is consistent with the fact that [bmpy][N(Tf)(2)] is a weaker hydrogen bond acceptor solvent than [bmpy][OTf]. Finally, a method by which [bmpy][N(Tf)(2)] may be recovered and reused for aromatic nitration has been demonstrated. 相似文献
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Dinitrodialkoxybenzene derivatives are important precursors for Schiff base macrocycles and a variety of other molecules. During our investigations, we have found that the dinitration reaction of 1,2-dialkoxybenzenes proceeds with unusual regioselectivity, giving exclusively the desired 1,2-dialkoxy-4,5-dinitrobenzene product, but we have been unable to find a good explanation for this result. The dinitration of 1,4-dialkoxybenzene derivatives also exhibits surprising regioselectivity that has hitherto been left unexplained. Herein, we report a detailed DFT analysis of the regioselective dinitration of both 1,2- and 1,4-dimethoxybenzene. These results show that the reaction mechanism likely involves a single electron transfer (SET) process. In the case of the former isomer, the regioselectivity is mainly determined by the symmetry of the HOMO of the aromatic moiety that defines the structure of the SHOMO of the aromatic radical cation formed by the SET process. In the case of the latter isomer, the selectivity is due mainly to solvation effects and may thus be altered depending on the solvent environment. Synthetic studies of the nitration of 1,4-dialkoxybenzene derivatives using different solvent conditions support this conclusion and provide practical information for tuning the regioselectivity of the reaction. 相似文献
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I.S. Gaponova G.B. Pariiskii T.V. Pokholok E.Ya. Davydov 《Polymer Degradation and Stability》2008,93(6):1164-1169
The mechanism of interaction of nitrogen dioxide with aromatic polyimides is considered by the example of polypyromellitimide. The formation of stable radicals of acylarylaminoxyl, iminoxyl and phenoxyl types has been detected by electron paramagnetic resonance spectroscopy. Acylarylaminoxyl radicals were detected in polypyromellitimide after its exposure to nitrogen dioxide at room temperature followed by pumping nitrogen dioxide from the samples. Iminoxyl and phenoxyl radicals were formed during thermolysis of the nitration products of the polymer at 373 K. The proposed mechanism is based on the reaction of dimers of nitrogen dioxide in the form of nitrosyl nitrate. It was observed that intermediate radical cations and nitric oxide were formed in the primary reaction of electron transfer from the polyimide to nitrosyl nitrate. The subsequent cage reactions with participation of radical cations and nitric oxide give nitroso compounds and nitrates which are precursors of stable nitrogen-containing and phenoxyl radicals. 相似文献
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T.V. Pokholok I.S. Gaponova E.Ya. Davydov G.B. Pariiskii 《Polymer Degradation and Stability》2006,91(10):2423-2428
By using the example of poly-m-phenylene isophthalamide, the mechanism of generation of stable nitrogen-containing radicals in aromatic polyamides in the presence of nitrogen dioxide is considered. The proposed mechanism is based on the reactions of dimers of nitrogen dioxide in the form of nitrosyl nitrate. As a result of a primary reaction of electron transfer from donor functional groups of macromolecules to nitrosyl nitrate, macromolecular radical cations and nitric oxide are formed. Amide groups and phenyl rings can act as electron donors. In the subsequent reactions with participation of radical cations, nitric oxide and nitrogen dioxide oximes, nitroso compounds and nitrites are formed. Generation of stable iminoxyl radicals occurs by reactions of oximes with nitrogen dioxide. Thermolysis of the polymer nitration products gives iminoxyl and acylarylaminoxyl radicals. The structure of iminoxyl radicals and features of dynamics of their formation have been confirmed by ab initio quantum-chemical calculations. 相似文献
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Erich Hunziker Philip C. Myhre John R. Penton Heinrich Zollinger 《Helvetica chimica acta》1975,58(1):230-256
The nitration of pentamethylbenzene in nitromethane has been studied under conditions that allow two mechanisms of nitration to be distinguished. One has been identified as nitration via the nitronium ion; the other nitration involves an oxidation of the molecular complex ArH-NO⊕PF6? by nitrogen dioxide followed by reaction of the aromatic substrate with the incipient nitronium ion and loss of nitric oxide. Either reaction can be made predominant by an appropriate change in the proportions of the reactants in the system. A consideration of the σ-complexes formed by attack of the electrophile at aromatic carbon bearing a methyl substituent can provide a satisfactory explanation for the features observed in this and in other nitrations of pentamethylbenzene. 相似文献
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Alexandra Romina Albunia Raffaele Borrelli Andrea Peluso 《Theoretical chemistry accounts》2000,104(3-4):218-222
Electron transfer (ET) from toluene to the nitronium ion in the region of van der Waals intermolecular distances has been
investigated by a quantum dynamical analysis performed on potential-energy surfaces computed at the ab initio multireference
configuration interaction level. The results show that ET is very fast, occurring on a timescale of a few picoseconds. This
has important implications for the mechanism of aromatic nitration: the ET path can compete efficiently with the direct attack
of the nitronium ion to the aromatic substrate to yield the Wheland intermediate and that could explain some unsettled points
in the mechanism of aromatic nitration.
Received: 16 September 1999 / Accepted: 3 February 2000 / Published online: 12 May 2000 相似文献
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Lenain P Mandado M Mosquera RA Bultinck P 《The journal of physical chemistry. A》2008,112(34):7898-7904
The interplay between aromatic electron delocalization and intermolecular hydrogen bonding is thoroughly investigated using multicenter delocalization analysis. The effect on the hydrogen bond strength of aromatic electron delocalization within the acceptor and donor molecules is determined by means of the interaction energies between monomers, calculated at the B3LYP/6-311++G(d,p) level of theory. This magnitude is compared to variations of multicenter electron delocalization indices and covalent hydrogen bond indices, which are shown to correlate perfectly with the relative values of the interaction energies for the different complexes studied. The multicenter electron delocalization indices and covalent bond indices have been computed using the quantum theory of atoms in molecules approach. All the hydrogen bonds are formed with oxygen as the acceptor atom; however, the atom bonded to the donor hydrogen has been either oxygen or nitrogen. The water-water complex is taken as reference, where the donor and acceptor molecular environments are modified by substituting the hydrogens and the hydroxyl group by phenol, furan, and pyrrole aromatic rings. The results here shown match perfectly with the qualitative expectations derived from the resonance model. 相似文献