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1.
次甲基硅SiH与HF反应的热力学及动力学性质研究 总被引:3,自引:0,他引:3
在量子化学对SiH与HF反应计算的基础上,运用统计热力学和Wigner校正的Eyring过渡态理论计算了该反应在200~2000K温度范围内的热力学函数、平衡常数、频率因子A和速率常数随温度的变化。计算结果表明该反应在低温下具有热力学优势,而在高温下具有动力学优势。该反应在研究的温度范围内是一放热、熵减少的反应,反应的速率常数随温度的升高而增大,且服从Arrhenius定律。 相似文献
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在量子化学对SiH与H2O和H2S反应计算的基础上,运用统计热力学和Wigner校正的Eyring过渡态理论,计算了上述两反应在200~2000 K温度范围内的热力学函数、平衡常数、频率因子A和速率常数随温度的变化。计算结果表明,两反应在低温下具有热力学优势,而在高温下具有动力学优势。比较两反应的计算结果发现,在相同的温度下,SiH与H2O反应比SiH与H2S反应放热较多,但速率常数却较小。SiH与H2O反应和前文报道的SiH与HF反应的比较表明,SiH与H2O反应放热较少,而且在相同温度下,速率常数也较小。 相似文献
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采用量子化学方法研究了十氢化萘低温燃烧的动力学机理,获得了脱氢反应、自由基加氧反应及1,5氢迁移反应等反应的动力学参数,并在CBS-QB3水平下获得了相关物种的热力学参数,通过过渡态理论计算获得了具有紧致过渡态反应的高压极限速率常数,而无能垒反应的速率常数则由变分过渡态理论得到.基于此机理分析了十氢化萘低温反应的动力学规律和热力学机制.相比于链烷烃和单环烷烃,十氢化萘自由基加氧反应的速率常数随温度变化较快,1,5-氢迁移反应的能垒较高,揭示了物质结构对反应动力学的影响.热力学平衡常数分析结果表明,在低温下十氢化萘自由基加氧反应起主导作用.通过拟合获得了所有反应Arrhenius形式的速率常数,这些参数可用于双环烷烃低温燃烧机理的构建和优化. 相似文献
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锗烯与甲醛环加成反应的理论研究 总被引:4,自引:0,他引:4
用从头算方法研究了单重态锗烯与甲醛环加成反应的机理,找到了反应的中间配合物和过渡态,并讨论了反应机理.在从头算的基础上,用统计热力学方法和过渡态理论计算了该反应在不同温度下的热力学函数的变化和动力学性质.结果表明,此反应由两步组成:(1)锗烯与甲醛反应生成了一中间配合物,是一无势垒的放热反应;(2)中间配合物异构化得到产物锗杂环氧甲烷,此步势垒经零点能校正后只有69.6kJ/mol(MP2/3-21G//3-21G).从热力学和动力学角度综合考虑,该反应在400~500K温度下进行为宜,此时,反应既有较大的自发趋势和平衡常数,又具有较快的反应速率. 相似文献
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硅烯与甲醛环加成反应的理论研究 总被引:3,自引:0,他引:3
本文用RHF/6-31G^*解析梯度方法研究了单重态硅烯与甲醛环加成反应的机理,用二级微扰方法对各构型的能量进行了相关能校正,并用统计热力学方法和过渡态理论计算了该反应在不同温度下的热力学函数的变化和动力学性质。结果表明,此反应历程由两步组成:1)硅烯与甲醛生成一中间配合物,是一无势垒的放热反应,2)中间配合物异构化为产物,此步势垒经零点能校正后只有51.4kJ·mol^-^1(MP2/6-31G^*//6-31G^*);从热力学和动力学的综合角度考虑,该反应在300~400K温度下进行为宜,如此,反应既有较大的自发趋势和平衡常数,又具有较快的反应速率。 相似文献
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锗烯与乙烯环加成反应的理论研究 总被引:8,自引:0,他引:8
用RHF/6-31G^*解析梯度方法研究了单重态锗烯与乙烯环加成反应的机理,用二级微扰方法对各构型的能量进行了相关能校正,并用统计热力学方法和过渡态理论计算了该反应在不同温度下的热力学函数的变化和动力学性质。结果表明,此反应历程由两步组成:1)锗烯与乙烯生成了一中间配合物,是一无势垒的放热反应,2)中间配合物异构化为产物锗杂环丙烷,此步势垒经零点能校正后为26.9kJ.mol^-^1(MP2/6-31G^*//6-31G^*);从热力学和动力学的综合角度考虑,该反应在200-300K温度下进行为宜,如此,反应既有较大的自发趋势和平衡常数,又具有较快的反应速率。 相似文献
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Wei Jiang SI Shu Ping ZHUO * Guan Zhi JU School of Chemical Engineering Shandong University of Technology Zibo State Key Laboratory of coordination Chemistry Nanjing University Nanjing 《中国化学快报》2004,15(5)
Silicon chemistry has been attracted more attention because of its applications to the production of thin silicon films and the etching of silicon wafers in micro-electronics1. Silylidyne (SiH), which plays an important role in plasma chemical vapor deposition (CVD) processes, has been investigated in experimental research2-5. The reaction mechanism of SiH insertion reaction with small molecules such as XH3 (X=N, P) was recently studied by means of M豯ler-Plesset perturbation theory6.… 相似文献
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Influence of Temperature on the Formation of Silver Nanoparticles by using a Seed‐Free Photochemical Method under Sodium‐Lamp Irradiation 下载免费PDF全文
Yen‐Ling Kuo Dr. Tzong‐Yuan Juang Shi‐Hise Chang Chin‐Ming Tsai Yen‐Shang Lai Li‐Chen Yang Cheng‐Liang Huang 《Chemphyschem》2015,16(15):3254-3263
Silver nanoparticles can be prepared by using a seed‐free photo‐assisted citrate reduction method under the irradiation of a sodium lamp. Under the same irradiation intensity, bath temperatures are crucial in influencing the reaction rate, morphologies of final products, and shape evolution of the silver nanostructures. For example, when the bath temperature is 80 °C, the product yields of silver nanoplates, nanorods, and nanodecahedra are 38±6 %, 35±10 %, and 12±8 %, respectively. However, when the bath temperature is 30 °C, the product yields of silver nanoplates, nanorods, and nanodecahedra are 6±3 %, 0 %, and 83±16 %, respectively. Time‐dependent UV/Vis spectra and TEM images show that silver nanoplates were formed at the earlier reaction stage and greatly decreased in amount at the later stage when the bath temperatures are less than or equal to 40 °C. This indicates that the silver nanoplates, which can be regarded as intermediates, are kinetically favored products. They are not thermodynamically favored products at these relatively low bath temperatures. The SERS spectra of crystal violet (CV) show that all the silver colloids synthesized at various temperatures exhibit good enhancement factors and that the colloids prepared at lower bath temperatures have a higher enhancement factor. 相似文献
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Experimental and theoretical investigation on the correlation between aqueous precursors structure and crystalline phases of zirconia 总被引:3,自引:0,他引:3
Nanometer zirconia powders were prepared by the precipitation method at different pHs and different reaction temperatures. X-ray results show that monoclinic zirconia is favored at pH 4 while tetragonal zirconia is favored at pH 9.5 at room temperature, and monoclinic zirconia is also favored at pH 9.5 and 70 °C reaction temperature, with the slow addition of alkali. Four models of zirconium complexes were applied to simulate the structural monomers in different pH solutions. Geometric parameters and Mulliken charge population were calculated by optimizing these complexes using the density functional theory (DFT/B3LYP). Theoretical analyses show that if Model I ([Zr(OH)2(H2O)4]2+ monomers) is favored in the aqueous precursor solution, it will be preferentially polymerized into monoclinic precursor structure irrespective of slow or quick alkali addition. Contrarily, if Model IV ([Zr(OH)7]3− monomers) is major in the aqueous precursor solution, tetragonal precursor structures are favored irrespective of slow or quick alkali addition. When Model II ([Zr(OH)4(H2O)2]0 monomers) and Model III ([Zr(OH)6]2− monomers), respectively, predominate in the aqueous precursor solution, they will be preferentially polymerized into tetragonal precursor structure at slow alkali addition, however, for quick alkali addition, they will be preferentially polymerized into monoclinic precursor structure. Our theoretical models well explain the present experimental results as well as previous experimental results, and allow building up a correlation between aqueous precursor structures and crystalline phases of zirconia. 相似文献
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Four new reaction pathways for polycyclic aromatic hydrocarbon growth from cyclopentadiene pyrolysis are proposed and investigated using the B3LYP/6-31G(d,p) level of theory. These pathways allow for the production of indene, naphthalene, and benzene through intramolecular addition, C-H beta-scission, and C-C beta-scission reaction mechanisms, respectively. Results show that the intramolecular addition channel is favored at low temperatures, and the C-H beta-scission channel and the newly identified C-C beta-scission pathway become significant when the temperature increases. These results are in qualitative agreement with the experimental results previously obtained by this research group indicating that the main product at low temperature is indene, while benzene and naphthalene production dominate at the high-temperature end. 相似文献
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Pasumansky L Collins CJ Pratt LM Nguyên NV Ramachandran B Singaram B 《The Journal of organic chemistry》2007,72(3):971-976
The influence of temperature and solvent effects on the reduction and amination mechanisms of iodomethane by lithium N,N-diisopropylaminoborohydride (iPr-LAB) was examined in varying concentrations of THF and dioxane. The reactions of benzyl chloride and trimethylsilyl chloride with iPr-LAB in THF were also studied. The amination of iodomethane is favored over reduction at low and room temperatures in pure THF and with increasing the amount of dioxane in THF. At higher temperatures, the reduction reaction appears to compete with the amination. In dioxane solvent, however, iodomethane yields exclusively the amination product regardless of temperature. On the other hand, reduction by iPr-LAB to the aminoborane is the only product observed in THF when benzyl chloride and trimethylsilyl chloride are used. To understand the solvent effects on the product distribution, ab initio and density functional theory (DFT) calculations were used to examine the mechanisms of reduction and amination of chloromethane and bromomethane by lithium dimethylaminoborohydride (LAB) in THF and dioxane. The results of these calculations show that the relative reaction barrier heights are significantly affected by the nature of the coordinated solvent molecule and thus lend support to the experimental observations. 相似文献
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Cobalt electrodeposition on polycrystalline palladium was studied at different temperatures using potentiostatic and voltammetric techniques. Temperature effect on kinetics parameters, diffusion coefficient, and charge transfer coefficient was analyzed. The values of nucleation rate and rate constant of the proton reduction reaction (k PR) increased with the temperature increment and the applied overpotential. The number of active nucleation sites was slightly affected with temperature increase. At higher temperatures, the larger k PR values suggested the proton reduction process is favored. The temperature effect on the values of the transfer coefficient was analyzed and a decrease in its value with the temperature increase was observed. From a Conway plot, it was observed that entropy change is the main factor that controls the kinetics of the reaction in this system. 相似文献
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《国际化学动力学杂志》2018,50(4):273-284
The mechanism of the reaction of ketene with methyl radical has been studied by ab initio CCSD(T)‐F12/cc‐pVQZ‐f12//B2PLYPD3/6‐311G** calculations of the potential energy surface. Temperature‐ and pressure‐dependent reaction rate constants have been computed using the Rice–Ramsperger–Kassel–Marcus (RRKM)–Master Equation and transition state theory methods. Three main channels have been shown to dominate the reaction; the formation of the collisionally stabilized CH3COCH2 radical and the production of the C2H5 + CO and HCCO + CH4 bimolecular products. Relative contributions of the CH3COCH2, C2H5 + CO, and HCCO + CH4 channels strongly depend on the reaction conditions; the formation of thermalized CH3COCH2 is favored at low temperatures and high pressures, HCCO + CH4 is dominant at high temperatures, whereas the yield of C2H5 + CO peaks at intermediate temperatures around 1000 K. The C2H5 + CO channel is favored by a decrease in pressure but remains the second most important reaction pathway after HCCO + CH4 under typical flame conditions. The calculated rate constants at different pressures are proposed for kinetic modeling of ketene reactions in combustion in the form of modified Arrhenius expressions. Only rate constant to form CH3COCH2 depends on pressure, whereas those to produce C2H5 + CO and HCCO + CH4 appeared to be pressure independent. 相似文献
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Ni-Cu/CeO2催化剂上乙醇水蒸气重整反应 总被引:8,自引:0,他引:8
研究了Ni-Cu/CeO2催化剂在乙醇水蒸气重整反应中的催化性能. 以具有高比表面积的CeO2为载体,用沉积沉淀法制备了一系列不同担载量的Ni, Cu双组分催化剂,采用X射线衍射、程序升温还原和透射电子显微镜对催化剂的晶相组成、还原性能和形貌进行了表征. 结果表明, CuO, NiO和CeO2的相互作用明显改善了NiO的分散. 适量CuO的加入使NiO分散度增大,颗粒明显变小,从而使催化剂具有更好的催化性能,但过多CuO的加入反而降低了催化剂的活性. Ni和Cu的催化性能差异较大, Ni具有优异的断裂C-C键性能,在低温下即可实现乙醇的完全转化,而在高温区则具有很好的甲烷重整性能,可获得很高的氢气产率; Cu在低温区倾向于使乙醇脱氢生成乙醛以及进一步脱羰基生成丙酮,在高温区也具有一定的乙醇裂解性能. 相似文献
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Both 4-phenyl 1-lithio-1,3-butadienes and 4-naphthyl 1-lithio-1,3-butadienes underwent highly efficient and selective intramolecular nucleophilic addition of the butadienyllithium to the aromatic rings, resulting in full dearomatization of the phenyl rings and partial dearomatization of the naphthyl rings. When the reactions were carried out at lower temperatures, ipso intramolecular nucleophilic attack took place exclusively to afford the spirocyclopentadiene derivatives upon hydrolysis or further treatment with a variety of electrophiles. 4-Naphthyl 1-lithio-1,3-butadienes and 4-phenyl 1-lithio-1,3-butadienes were found to proceed in this reaction under similar conditions, with the former being faster even at -78 degrees C. However, when the reaction of 4-naphthyl 1-lithio-1,3-butadienes was carried out at higher temperatures, such as 75 degrees C, an interesting skeletal rearrangement took place to afford the vicinal attack products, tetrasubstituted phenanthrenes, via a dearomatization/rearomatization process. Mechanistic investigation revealed that the kinetically favored ipso attack intermediates might undergo thermal skeletal rearrangement via 1,2-alkyl shift. 相似文献
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An induced circular dichroism (ICD) solution study on the orientation of ferrocenyl azide within the beta-cyclodextrin cavity is described. In DMSO, ferrocenyl azide prefers an axial inclusion, whereas in ethylene glycol and DMSO/H2O = 50/50 an equatorial alignment dominates. As shown by temperature-dependent ICD spectra, at lower temperatures ferrocenyl azide adopts preferentially an equatorial arrangement, whereas at higher temperatures an axial one is favored. Temperature and solvent effects on the co-conformation of ferrocene noncovalently bound to cyclodextrin have never been observed before. 相似文献