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用密度泛函理论(DFT)方法在B3LYP/6-31G*水平上研究了苯甲醛肟与炔丙醇加成反应的微观机制和热力学、动力学行为. 结果表明, 在苯甲醛肟与炔丙醇加成反应过程中, 8个可能反应通道的过渡态中均形成非平面五元环结构, 其中苯甲醛肟的Z、E构型特征得到了部分保留, 但主要部分的键长、键角均发生了变化, 电荷也进行了重新分布. 苯甲醛肟以羟基型参与反应的4个反应通道均为吸热反应和热力学非自发过程, 它们均具有较高的反应势垒、较慢的反应速率和较小的平衡常数; 而以离子型参与反应的四个反应通道均为放热反应和热力学自发过程, 它们的反应势垒较低, 反应速度较快, 平衡常数也较大, 故苯甲醛肟应主要以离子型参与反应. 炔丙醇的两种取向对应着加成反应的两种产物, 反应达到平衡后, 3-羟甲基二氢异噁唑为主要产物. 相似文献
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钯催化的交叉偶联反应是非常实用的合成新方法.文章给出了Heck反应、Negishi反应和Suzuki反应的概念,对其反应机理作了详细的说明,并对其在复杂化合物和天然产物全合成中的应用作了评价. 相似文献
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V. I. Anikeev D. A. Stepanov A. Ermakova 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2011,85(8):1336-1346
Calculations of thermodynamic data are performed for fatty acid triglycerides, free fatty acids, and fatty acid methyl esters,
participants of the transesterification reaction of vegetable oils that occurs in methanol. Using the obtained thermodynamic
parameters, the phase diagrams for the reaction mixture are constructed, and the chemical equilibria of the esterification
reaction of free fatty acids and the transesterification reaction of fatty acid triglycerides attained upon treatment with
supercritical methanol are determined. Relying on our analysis of the obtained equilibria for the esterification reaction
of fatty acids and the transesterification reaction of triglycerides attained upon treatment with lower alcohols, we select
the optimum conditions for performing the reaction in practice. 相似文献
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尽管已有大量化学反应数据可供使用,但化学家仍常常感到很难便捷地从中得到所需的信息.这主要是由于反应数据库基于结构的检索方法与化学家解决问题的方法相去甚远.为解决这一问题而发展了一种通过对反应进行二级分类得到精细描述反应知识的层次模型的方法.第一次分类时不同的同类反应都在由一组普适性好的称作反应结构一级描述符构成的空间中进行.在第一次分类结果的基础上,得到每一类反应的公共结构特征作为第二次分类的结构描述符,利用它们进行更精细的分类,即可从原始反应数据中得到所需的基核反应.由特定反应、基核反应和基型反应就可将反应知识更合理地组织在同类反应知识库中,使它们得到更好的利用. 相似文献
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Direct dynamics within the framework of DFT was used to study the long-time puzzling mechanism of the reaction between F2 and ethylene. Three types of reactions are widely accepted : F atom elimination reaction, HF elimination reaction and the addition reaction. Several reaction mechanisms have been proposed, but only the radical mechanism can reasonably explain the initial reaction at low temperature. In this article, our calculations support the radical mechanism and the reaction mechanisms of the three reactions, and they are described in detail by trajectory simulation. The reactions in a cryogenic matrix with the reaction mechanism were also discussed. 相似文献
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用G3(MP2)//B3PW91/6-311G(d,p)双级别方法研究了CH_3自由基与C_2H5_CN的反应机理和动力学性质.计算表明反应存在抽氢、加成-消除和取代3种机理7条反应通道.用CVT方法计算了所有反应通道在1 000K~3 000K温度范围内的速率常数,结果表明计算值与实验值符合得很好. 相似文献
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质谱因具有分辨率高、灵敏度好、响应快速以及结构鉴定能力强等特点,近年来在反应监测研究领域应用广泛.本文介绍了基于质谱的经典在线直接采样实时监测方案;综合评述了常压质谱离子化技术在反应监测领域的发展和应用,主要包括基于常压质谱的快反应监测、微滴加速在长时间反应研究中的应用,以及其它常压质谱在反应监测中的应用;并对质谱在反应监测研究领域面临的挑战和发展趋势进行了总结和展望. 相似文献
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There are two different views on the definition of reaction molecularity in physical chemistry textbooks and related literatures so far. We give a deep discussion about this conception herein. Starting with the development of chemical kinetics and the definition of elementary reaction and state-state reaction, we clarify that elementary reaction and state-state reaction are the conceptions belonging to macro-and micro-systems, respectively, and reaction molecularity is also belonging to micro-conception. Based on this conclusion, we think that the more reasonable definition of reaction molecularity should be "the number of chemical particles that take part in a state-state reaction (or an elementary chemi-physical reaction) as a reactant". 相似文献
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Xiao-Yan Tang Hong-Xi Li Jin-Xiang Chen Zhi-Gang Ren Jian-Ping Lang 《Coordination chemistry reviews》2008,252(18-20):2026-2049
The chemistry of metal complexes of the zwitterionic ammonium thiolates has expanded dramatically in the recent years. This review is intended to summarize the synthesis and crystal structures of groups 11 and 12 metal zwitterionic ammonium thiolate complexes. Seven methods for the synthesis of these metal complexes of the zwitterionic ammonium thiolates are outlined: proton transfer reaction, precursor reaction, ligand exchange reaction, oxidation–reduction reaction, solid-state reaction, electrochemical reaction and hydro(solvo)thermal reaction. These metal complexes of the zwitterionic ammonium thiolates are classified according to the number of metal atoms; their specific structures are briefly discussed. 相似文献
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We compare free energy calculations for the methyl transfer reaction catalyzed by catechol O-methyltransferase using the quantum mechanical/molecular mechanical free energy method with implicit and explicit solvents. An analogous methylation reaction in a solution is also studied. For the explicit solvent model, we use the three-point transferable intermolecular potential model, and for the implicit model, we use the generalized Born molecular volume model as implemented in CHARMM. We find that activation and reaction free energies calculated with the two models are very similar, despite some structural differences that exist. A significant change in the polarization of the environment occurs as the reaction proceeds. This is more pronounced for the reaction in a solution than for the enzymatic reaction. For the enzymatic reaction, most of the changes take place in the protein rather than in the solvent, and, hence, the benefit of having an instantaneous relaxation of the solvent degrees of freedom is less pronounced for the enzymatic reaction than for the reaction in a solution. This is a likely reason why energies of the enzyme reaction are less sensitive to the choice of atomic radii than are energies of the reaction in a solution. 相似文献
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Two possible lower barrier reaction pathways in the reaction HF HOBO→H2O FBO are predicated by means of MP2 and CCSD(T)(single-point)methods.In the two channels,two stable intermediates are located,and thus,they are multi-step channels,which are more favorable in energy than direct single-step reaction pathway predicated by previous theoretical study,Therefore,the two pathways should be main reaction channels in experiments. 相似文献
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本文首次提出了化学反应过程中几何可能性的定量研究.在下列条件下:(1)反应过程中,惰性配位体的键长,立体角系数等参数保持不变;(2)惰性配位体的压缩性很小;(3)在不压缩其它配位体的条件下,某一配位体在配位球面漂移所需的活化能低于这一配位体所形成的化学键断裂时所需的相应能量.我们提出动态堆积模型.以此来模拟反应过程中各个配位体间的相对位置和运动、配位体之间间隙的大小与受压缩的程度,并计算在反应中间过程中能够容纳新的配位体的最大空缺.考虑到使惰性配位体压缩将产生很大的空间势垒,以UCp3X为例说明了Lewis碱的配合与解离;金属-碳σ键的热分解以及一氧化碳插入反应的可能性. 相似文献
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Sahasrabudhe K Gracias V Furness K Smith BT Katz CE Reddy DS Aubé J 《Journal of the American Chemical Society》2003,125(26):7914-7922
An asymmetric equivalent of the Schmidt reaction permits stereocontrol in ring expansions of symmetrical cyclohexanones. The procedure involves the reaction of chiral 1,2- and 1,3-hydroxyalkyl azides with ketones under acid catalysis; the initial reaction affords an iminium ether that can be subsequently opened with base. A systematic study of this reaction is reported, in which ketone substrates, chiral hydroxyalkyl azides, and reaction conditions are varied. Selectivities as high as ca. 98:2 are possible for the synthesis of substituted caprolactams, with up to 1,7-stereoselection involved in the overall process. The fact that either possible migrating carbon is electronically identical provides an unusual opportunity to study a ring-expansion reaction controlled entirely by stereoelectronic factors. The mechanism of the reaction and the source of its stereoselectivity are also discussed. 相似文献