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Polypyromellitimides have been synthesized from carbazole and N-benzylcarbazole by a two-step procedure involving ring-opening polyaddition with pyromellitic dianhydride and subsequent thermal cyclodehydration. The physicochemical, thermal and dielectric properties of the polymers have been studied. The various N-substituents, such as N-methyl and N-benzyl groups of the carbazole moieties, exert some influence on the overall thermal and dielectric properties of the polyimides. The influence has been rationalized in terms of gross structural characteristics. 相似文献
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Iwao Omae 《Journal of organometallic chemistry》2007,692(13):2608-2632
There are three types of reactions with intramolecular five-membered ring compounds in organic syntheses: The first type is reactions involving intramolecular five-membered ring compounds which are utilized for the ease of synthesis of these compounds and the stability of the products. The second is reactions performed via intramolecular five-membered ring intermediates, because such intermediates are very reactive and labile compounds. The third is the metal-catalyzed reactions with the intramolecular five-membered ring compounds because these metal compounds have catalytic activities. The third type reactions involving intramolecular five-membered ring pincer compounds are also provided.The first type reactions include carbonylations, alkenylations, alkynylations, acylations, isocyanations, Diels-Alder reactions, etc. The second type reactions include carbonylations, cross-coupling reactions, hydroacylations, ring expansion reactions, carbocyclizations, etc. The third type reactions include cross-coupling reactions, rearrangements, metatheses, reductions, Michael reactions, dehydrogenations, Diels-Alder reactions, etc. 相似文献
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2,3-联烯醇是一类含1,2-二烯官能团和羟基的化合物, 具有很高的反应活性, 它及其衍生物是一类重要的联烯化合物. 概述了2,3-联烯醇及其衍生物的反应, 包括2,3-联烯醇在过渡金属催化下的自身异构环化反应、钯催化的偶联反应、钌催化的环羰基化反应、不同条件下不同方式的扩环反应、亲电试剂参与的反应、分子内环加成反应、自由基反应等和2,3-联烯醇衍生物在零价钯催化下基于亚甲基-π-烯丙基钯中间体生成联烯或1,3-共轭二烯的区域选择性反应, SN2'类型的加成-消除反应, 二价钯催化下的分子内环化反应以及重排反应等. 相似文献
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Chemical kinetics of reactions in the unfrozen solution of ice 总被引:1,自引:0,他引:1
Some reactions are accelerated in ice compared to aqueous solution at higher temperatures. Accelerated reactions in ice take place mainly due to the freeze-concentration effect of solutes in an unfrozen solution at temperatures higher than the eutectic point of the solution. Pincock was the first to report an acceleration model for reactions in ice,1 which successfully simulated experimental results. We propose here a modified version of the model for reactions in ice. The new model includes the total molar change involved in reactions in ice. Furthermore, we explain why many reactions are not accelerated in ice. The acceleration of reactions can be observed in the cases of (i) second- or higher-order reactions, (ii) low concentrations, and (iii) reactions with a small activation energy. Reactions with a buffer solution or additives in order to adjust ion strength, zero- or first-order reactions, or reactions containing high reactant concentrations are not accelerated by freezing. We conclude that the acceleration of reactions in the unfrozen solution of ice is not an abnormal phenomenon. 相似文献
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Kizashi Yamaguchi 《Chemical physics letters》1974,28(1):93-97
The insertion and abstraction reactions are investigated on the basis of the Heisenberg model. These reactions are characterized as spin-symmetry forbidden and allowed reactions, respectively. It is pointed out that free radical reactions occur readily when there is no spin degeneracy in the course of these reactions. The rule obtained is discussed in relation to the orbital symmetry conservation rule for concerted reactions. 相似文献
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Fluorinated alcohols have been widely used in the synthetic organic chemistry over the past decades. The unique properties such as the strong hydrogen‐bonding donor ability and low nucleophilicity allow them to promote organic reactions in the absence of any catalyst. These approaches have distinct advantages in terms of operational simplicity, practicability and environmental friendliness. Reactions promoted by fluorinated alcohols, including nucleophilic substitution reactions, annulation reactions, electrophilic reactions, dearomatization reactions, functionalization of multiple bond, epoxidation reactions and miscellaneous reactions have been summarized in this account. 相似文献
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IntroductionThe nitro derivatives of methylbenzene are an important category of explosives, in whichTNT (2, 4, 6--trinitrotoluene) is widely--used. It is widely accepted that methyl hydrogen in m....troaromatlcs is quite active, which influences the impact sensitivity of an explosive. Gonzalezet al. [IJ found methyl substitution increases the decomposition rate over that of nitrobenzeneby an order of magnitude. Much effort has been devoted to relating electronic structure and.....impact sens… 相似文献
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Iwao Omae 《应用有机金属化学》2009,23(3):91-107
Group 9 metal compounds in organic synthesis have two characteristic reactions. The first occurs because the group 9 metals have a high affinity to carbon–carbon or carbon–nitrogen π‐bonds. The first type of characteristic reactions in these group 9 metal compounds includes Pauson–Khand reactions, the Pauson–Khand‐type reactions ([2 + 2 + 1] cyclization), the other cyclizations and coupling reactions. The second occurs because the group 9 metals have a high affinity to carbonyl groups. The second type of characteristic reactions includes carbonylations such as hydroformylations, the carbonylations of methanol, amidocarbonylations and other carbonylations. The first characteristic reactions are applied for the synthesis of fine chemicals such as pharmaceuticals and agrochemicals. However, the second characteristic reactions are utilized not only for fine chemicals but also for important bulk commodity chemicals such as aldehydes, carboxylic acids and alcohols. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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T. G. Denisova 《Kinetics and Catalysis》2007,48(5):609-614
The enthalpies and equilibrium constants of the exchange reactions of peroxy radicals with hydroperoxides of various structures are calculated. The experimental data on the reactions of hydrogen atom abstraction by the peroxy radicals from the hydroperoxides are analyzed, and the kinetic parameters characterizing these reactions are calculated using the intersecting parabolas method. The activation energies and rate constants for nine reactions of H atom abstraction by a peroxy radical from the OOH group of a peroxide are calculated using the above parameters. The geometric parameters of the transition states for the reactions are calculated. The low triplet repulsion plays an important role in the fast occurrence of the reactions. The polar interaction in the transition state is manifested in the reactions of the peroxy radicals with hydroperoxides containing a polar group. 相似文献
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自由基正离子含有一个正电荷和一对未成对电子,是很多有机化学反应的重要的活性中间体。文章综述了近几年自由基正离子反应研究进展,主要包括化学氧化剂诱导的自由基正离子反应、可见光诱导的自由基正离子反应、电诱导的自由基正离子反应等方面的研究。 相似文献
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Iwao Omae 《Coordination chemistry reviews》2011,255(1-2):139-160
Cyclocarbonylation reactions proceed mainly by the coupling reactions of carbonylation components with cyclization components having an unsaturated π-electron bond, in the presence of transition metal compounds. The representative reactions are cyclocarbonylation of alkynes by carbon monoxide such as Pauson–Khand reactions, hetero Pauson–Khand reactions, cyclocarbonylation of alkynyl alcohols, cyclocarbonylation of alkynyl amines, cyclocarbonylative alkyne–alkyne coupling reactions, and reductive cyclocarbonylation of alkynes. The other reactions are cyclocarbonylation of alkenes by carbon monoxide such as alkene–alkene coupling reactions, cyclocarbonylation with aldehydes, ketones, amines or imines, cyclocarbonylation of alkenyl alcohols. Carbonylation via cyclometalation, carbonylative ring expansion reactions, cyclocarbonylation by aldehydes, carboxylic acids or carboxylic acid esters are also cyclocarbonylation reactions. These reactions are conveniently used for organic syntheses, especially, for the syntheses of pharmaceutical intermediates. 相似文献
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This concept article provides a brief outline of the concept of flash chemistry for carrying out extremely fast reactions in organic synthesis by using microreactors. Generation of highly reactive species is one of the key elements of flash chemistry. Another important element of flash chemistry is the control of extremely fast reactions to obtain the desired products selectively. Fast reactions are usually highly exothermic, and heat removal is an important factor in controlling such reactions. Heat transfer occurs very rapidly in microreactors by virtue of a large surface area per unit volume, making precise temperature control possible. Fast reactions often involve highly unstable intermediates, which decompose very quickly, making reaction control difficult. The residence time can be greatly reduced in microreactors, and this feature is quite effective in controlling such reactions. For extremely fast reactions, kinetics often cannot be used because of the lack of homogeneity of the reaction environment when they are conducted in conventional reactors such as flasks. Fast mixing using micromixers solves such problems. The concept of flash chemistry has been successfully applied to various organic reactions including a) highly exothermic reactions that are difficult to control in conventional reactors, b) reactions in which a reactive intermediate easily decomposes in conventional reactors, c) reactions in which undesired byproducts are produced in the subsequent reactions in conventional reactors, and d) reactions whose products easily decompose in conventional reactors. The concept of flash chemistry can be also applied to polymer synthesis. Cationic polymerization can be conducted with an excellent level of molecular-weight control and molecular-weight distribution control. 相似文献
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在无机化学领域中,水解反应早已为人熟知,但很少被系统讨论。本文将无机化学中的水解反应进行汇总并分类:水溶液中的水解反应,固态物质加热时的水解反应和水解缩合反应。本文介绍了水溶液中水解反应的水解机理、水解反应及水解反应产物在生产、生活中的应用。 相似文献
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Dr. Xianjun Xu Ling Zhong Prof. Huangdi Feng Prof. Erik V. Van der Eycken 《Chemical record (New York, N.Y.)》2023,23(10):e202300101
The highly efficient construction of complicated heterocyclic frameworks in an atom- and step-economic manner is still one of the cores of synthetic chemistry. Dearomatization reactions show the unique advantage for the construction of functionalized heterocycles and have attracted widespread attention over the past two decades. The metal-free approach has proved to be a green and sustainable paradigm for the synthesis of spirocyclic, polycyclic and heterocyclic scaffolds, which are widely present in natural products and bioactive molecules. In this review, the advances in the recent six years (2017–2023) in metal-free dearomatization reactions are highlighted. Emphasis is placed on developments in the field of organo-catalyzed dearomatization reactions, oxidative dearomatization reactions, Brønsted acid- or base-promoted dearomatization reactions, photoredox-catalyzed dearomatization reactions, and electrochemical oxidation dearomatization reactions. 相似文献
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综述了高压下溶液中化学反应的活化体积△V~≠的定义和测定方法,以及作为配合物取代反应、异构化反应、电子转移反应和光化学反应机理的判据。 相似文献