共查询到20条相似文献,搜索用时 78 毫秒
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1,2-环氧化物开环反应是化学类各专业有机化学课程中的重要教学内容,教材中的描述缺少定量、直观信息,学生通常采用机械记忆方式予以学习,不能完全理解相关的反应机制。本文设计了一个用理论化学方法研究化学反应的典型案例,通过量子化学计算探讨了酸、碱催化1,2-环氧化物开环反应的分子机制,揭示了反应的热力学和动力学性质,描绘了反应过程的直观物理图像,给出了理解反应区域选择性的定量信息。论文将计算量子化学与有机化学教学内容有机融合,不仅有助于学生加深对化学基本概念和基础理论的理解,而且有助于学生开阔视野、拓展思路,使学生充分认识到理论计算是开展化学研究的重要手段。 相似文献
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介绍一个为化学专业本科生设计的、运用通用量子化学软件Gaussian和GaussView完成的计算化学实验.实验内容包括最基本的构型优化、频率计算和电子结构分析.旨在通过本实验,使学生初步掌握用量子化学计算方法研究分子结构和性质的基本过程,并能在将来的科研工作中学以致用. 相似文献
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介绍一个面向高年级本科生的计算化学实验。通过利用量子化学计算,确定嘧啶碱基的酸碱性质以及它们与水分子之间的相互作用能,构建氢键复合物分子间相互作用与分子酸碱性之间的定量关系,使学生对分子的酸碱性、分子间相互作用、分子识别之间的关系有一定的直观认识。该实验有助于学生梳理课堂学到的碎片化知识,提升学生逻辑分析及创新能力。 相似文献
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利用文献结果,用统计热力学和过渡态理论计算了CF3CO和CF3C(O)O自由基分解反应的热力学和动力学数据。计算结果表明,计算值与最新实验数据甚相符合,并据此判断,CF3CO和CF3C(O)O均很不稳定,不可能参加O3分解的循环催化反应。 相似文献
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Alberto Escudero 《Journal of solid state chemistry》2007,180(4):1436-1445
This paper examines the structural changes with temperature and composition in the Sc2Si2O7-Y2Si2O7 system; members of this system are expected to form in the intergranular region of Si3N4 and SiC structural ceramics when sintered with the aid of Y2O3 and Sc2O3 mixtures. A set of different compositions have been synthesized using the sol-gel method to obtain a xerogel, which has been calcined at temperatures between 1300 and 1750 °C during different times. The temperature-composition diagram of the system, obtained from powder XRD data, is dominated by the β-RE2Si2O7 polymorph, with γ-RE2Si2O7 and δ-RE2Si2O7 showing very reduced stability fields. Isotherms at 1300 and 1600 °C have been analysed in detail to evaluate the solid solubility of the components. Although, the XRD data show a complete solid solubility of β-Sc2Si2O7 in β-Y2Si2O7 at 1300 °C, the 29Si MAS-NMR spectra indicate a local structural change at x ca. 1.15 (Sc2−xYxSi2O7) related to the configuration of the Si tetrahedron, which does not affect the long-range order of the β-RE2Si2O7 structure. Finally, it is interesting to note that, although Sc2Si2O7 shows a unique stable polymorph (β), Sc3+ is able to replace Y3+ in γ-Y2Si2O7 in the compositional range 1.86?x?2 (where x is Sc2−xYxSi2O7) as well as in δ-Y2Si2O7 for compositions much closer to the pure Y2Si2O7. 相似文献
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完全还原的NixCu1-xFe2O4(x=0.25,0.5,0.75)可用来分解CO2。采用共沉淀法制备了NixCu1-xFe2O4(x=0.25,0.5,0.75)系列铁酸盐的纳米微粒,利用H2-TG数据分析NixCu1-xFe2O4(x=0.25,0.5,0.75)中Cu2+的还原反应动力学数据,得出表观活化能Ea并不是单纯随着Ni2+或Cu2+含量的变化而变化,当x=0.25时反应活化能具有最大值。通过CO2-TG比较不同样品经H2完全还原后分解CO2的活性,得出Ni0.5Cu0.5Fe2O4具有最低的起始反应温度和最大的分解活性,并采用XRDRietveld拟合方法对Ni0.5Cu0.5Fe2O4的完全还原产物和分解CO2产物进行物相分析。 相似文献
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以双胺类配体[K2(L)(THF)2] (1)(L=Ph2Si(NAr)2, Ar=2, 6-iPr2C6H3)与二价稀土YbI2(THF)2的交换反应得到2个不同类型的化合物[Yb(L)(THF)3] (2)和{Yb(L)2[K(THF)2]2} (3)。对化合物进行X-射线单晶结构解析, 核磁共振和元素分析表征。研究结果表明:化合物2中, 通过1个双齿含氮配体和3个中性THF分子配位, 以五配位模式稳定二价镱稀土中心。而化合物3中二价稀土镱是与2个螯合胺类配体配位, 以共平面、四配位模式稳定其金属中心。K+恰好在配体的2个苯环之间, 形成独特的三明治结构, 有助于化合物的稳定。 相似文献
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以双胺类配体[K2(L)(THF)2] (1)(L=[Ph2Si(NAr)2]2-, Ar=2,6-iPr2C6H3)与二价稀土YbI2(THF)2的交换反应得到2个不同类型的化合物[Yb(L)(THF)3] (2)和{Yb(L)2[K(THF)2]2} (3)。对化合物进行X-射线单晶结构解析, 核磁共振和元素分析表征。研究结果表明:化合物2中, 通过1个双齿含氮配体和3个中性THF分子配位, 以五配位模式稳定二价镱稀土中心。而化合物3中二价稀土镱是与2个螯合胺类配体配位, 以共平面、四配位模式稳定其金属中心。K+恰好在配体的2个苯环之间, 形成独特的三明治结构, 有助于化合物的稳定。 相似文献
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I. A. Baidina I. A. Druzhinina S. A. Gromilov V. V. Tatarchuk 《Journal of Structural Chemistry》2004,45(2):335-339
Single crystals of the [PdL2(NO2)2] complex were obtained for the first time, where L is di-n-butylsulfide. Single crystal and powder diffraction studies provided new data on the molecular and crystal structure of this compound. 相似文献
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Two uranyl tellurates, AgUO2(HTeO5) (1) and Pb2UO2(TeO6) (2), were synthesized under hydrothermal conditions and were structurally, chemically, and spectroscopically characterized. 1 crystallizes in space group Pbca, a=7.085(2) Å, b=11.986(3) Å, c=13.913(4) Å, V=1181.5(5) Å3, Z=8; 2 is in P2(1)/c, a=5.742(1) Å, b=7.789(2) Å, c=7.928(2) Å, V=90.703(2) Å3, and Z=2. These are the first structures reported for uranyl compounds containing tellurate. The U6+ cations are present as (UO2)2+ uranyl ions that are coordinated by O atoms to give pentagonal and square bipyramids in compounds 1 and 2, respectively. The structural unit in 1 is a sheet consisting of chains of edge-sharing uranyl pentagonal bipyramids that are one bipyramid wide, linked through the dimers of TeO6 octahedra. In 2, uranyl square bipyramids share each of their equatorial vertices with different TeO6 octahedra, giving a sheet with the autunite-type topology. Sheets in 1 and 2 are connected through the low-valence cations that are located in the interlayer region. The structures of 1 and 2 are compared to those of uranyl compounds containing octahedrally coordinated cations. 相似文献
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Mahboubeh Rostami Ahmad R. Khosropour Valiollah Mirkhani Iraj Mohammadpoor-Baltork Majid Moghadam Shahram Tangestaninejad 《Comptes Rendus Chimie》2011,14(10):869-877
Di[1,6-bis(3-methylimidazolium-1-yl)hexane] decatungstate dihydrate ([C6(MIm)2]2W10O32. 2H2O) as a new family of polyoxometalate-based dicationic ionic liquids (POM-DIL) is synthesized and employed as a novel and powerful heterogeneous catalyst in the synthesis of 4-arylidene-2-phenyl-5(4)-oxazolones (azlactones) under ultrasound-assisted solvent-free condition. On the basis of the results, the products were obtained in excellent yields under mild condition. Utilization of easy work-up and purification make it very interesting from an economic perspective. Moreover, a recycling study confirmed that the catalyst can be reused multiple times without significant loss of its activity. 相似文献
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Polymerizations of ethylene have been carried out by using Cp2*Zr(NMe2)2 (Cp*=C5Me5) compound combined with common alkyl aluminums (AlR3) and methylaluminoxane (MAO) as cocatalysts. The AlMe3 cocatalyzed system showed no activity due to the formation of stable but inactive heterodinuclear [Cp2*2Zr(μ-Me)2AlMe2]+ cations; however, the bulkier AlR3 [AlEt3, Al(i-Bu)3 and Al(i-Bu)2H] cocatalyzed systems showed very high activities. Especially, Cp2*Zr(NMe2)2/Al(i-Bu)3 catalyst showed higher catalytic activity and produced higher molecular weight (MW) polymer than Cp2*Zr(NMe2)2/MAO catalyst, demonstrating both MAO and bulky AlR3 are effective cocatalysts for Cp2*Zr(NMe2)2 compound. 相似文献
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Yuriy B. Tyvanchuk Ute Ch. Rodewald Rainer Pöttgen 《Journal of solid state chemistry》2008,181(4):878-883
The new rare earth metal (RE)-nickel-indides Dy5Ni2In4 and RE4Ni11In20 (RE=Gd, Tb, Dy) were synthesized from the elements by arc-melting. Well-shaped single crystals were obtained by special annealing sequences. The four indides were investigated by X-ray diffraction on powders and single crystals: Lu5Ni2In4 type, Pbam, Z=2, a=1784.2(8), b=787.7(3), c=359.9(1) pm, wR2=0.0458, 891 F2 values, 36 variables for Dy5Ni2In4, U4Ni11Ga20 type, C2/m, a=2254.0(9), b=433.8(3), c=1658.5(8) pm, β=124.59(2)°, wR2=0.0794, 2154 F2 values, 108 variables for Gd4Ni11In20, a=2249.9(8), b=432.2(1), c=1657.9(5) pm, β=124.59(2)°, wR2=0.0417, 2147 F2 values, 108 variables for Tb4Ni11In20, and a=2252.2(5), b=430.6(1), c=1659.7(5) pm, β=124.58(2)°, wR2=0.0550, 2003 F2 values, 109 variables for Dy4Ni10.80In20.20. The 2d site in the dysprosium compound shows mixed Ni/In occupancy. Most nickel atoms in both series of compounds exhibit trigonal prismatic coordination by indium and rare earth atoms. Additionally, in the RE4Ni11In20 compounds one observes one-dimensional nickel clusters (259 pm Ni1-Ni6 in Dy4Ni10.80In20.20) that are embedded in an indium matrix. While only one short In1-In2 contact at 324 pm is observed in Dy5Ni2In4, the more indium-rich Dy4Ni10.80In20.20 structure exhibits a broader range in In-In interactions (291-364 pm). Together the nickel and indium atoms build up polyanionic networks, a two-dimensional one in Dy5Ni2In4 and a complex three-dimensional network in Dy4Ni10.80In20.20. These features have a clear consequence on the dysprosium coordination, i.e. a variety of short Dy-Dy contacts (338-379 pm) in Dy5Ni2In4, while the dysprosium atoms are well separated (430 pm shortest Dy-Dy distance) within the distorted hexagonal channels of the [Ni10.80In20.20] polyanion of Dy4Ni10.80In20.20. The crystal chemistry of both structure types is comparatively discussed. 相似文献