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采用密度泛函方法对3-甲硫基-4-氰基-5-氨基吡唑与碘甲烷反应的机理进行了研究. 提出了两种可能的反应途径: 反应途径Ⅰ为反应物先脱去吡唑上的质子, 生成阴离子中间物, 然后碘甲烷分别进攻中间物吡唑环上的2个氮原子, 生成两种异构产物; 反应途径Ⅱ为反应物通过分子间氢转移存在两种异构体, 碘甲烷直接进攻每个异构反应物吡唑上的氮原子, 形成中间物, 然后脱去碘化氢, 生成产物. 计算结果表明, 途径Ⅱ应为主要反应途径. 还找出了两种异构产物间甲基迁移反应的过渡态, 得出该反应的活化能为278.5 kJ/mol, 在常温下甲基迁移反应不容易进行. 相似文献
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对金属元素Au采用LanL2DZ基组,对非金属元素C,H,O,Cl采用6-31G*和6-311++G**基组,用密度泛函理论的B3LYP、B3PW91、UB3LYP方法和二阶微扰理论MP2方法研究了不同氧化态的金催化剂催化2-炔丙基苯酮与苯炔环化反应的机理.结果表明:在AuCl和AuCl3的作用下,反应均能通过[4+2]和[3+2]途径生成产物.但在AuCl催化下,[4+2]反应途径比[3+2]反应途径具有更低的活化自由能,反应主要通过[4+2]途径进行;而在AuCl3催化下,[4+2]反应途径与[3+2]反应途径的活化自由能相近,反应通过两条途径竞争生成产物.比较AuCl和AuCl3的催化效果发现,不同氧化态的金催化剂改变了反应的机理,该反应的活化自由能在AuCl作用下比在AuCl3作用下低11.18 kJ·mol-1.对于该反应,AuCl表现出了更好的催化活性.这些计算结果和实验现象相吻合. 相似文献
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甲硅硫醇兼有有机硅和有机硫化物的特点。本文对它的脱氢反应途径进行微观动力学解析,并与甲硫醇的脱氢反应引进行了比较,结果表明它们的反应途径相似。活化能对甲硅硫醇的脱氢反应有利,而活化熵和频率因子则对甲硫醇的脱氢反应有利。 相似文献
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用从头计算法辅以能一梯度法优化了反应C_2H+H_2→C_2H+H的过渡态,用福井谦一的理论求出反应途径,用反应途径哈密顿理论及正则变分过渡态理论计算沿反应途径的动力学性质和反应速率常数。在此基础上对涉及振动激发的选态反应速率常数进行计算,所得结果与现有的实验结果相符合。 相似文献
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CH+H_2→CH_3的MCSCF和VTST研究 总被引:1,自引:0,他引:1
用福井的内禀反应坐标理论和MCSCF/6-31G方法计算了CH+H_2→CH_3的反应途径。在此基础上,计算了沿反应途径的动态学行为和变分过渡态理论(VTST)的速率常数(包括CVT,ICVT,/VT和US方法)。结果表明,反应的返回效应不大;但反应途径的曲率效应较大,它对速率常数影响较大,理论研究必须考虑这一因素。 相似文献
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本文用HF/STO-3G解析梯度方法计算了甲基环丙烷卡宾重排反应的8个构型,它们代表4个反应类型.计算结果表明,甲基的H原子对卡宾碳的1,3迁移遵从端端告拢机理.环丙烷上的H原子1,2迁移活性遵从夹有相似文献
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本文报道在交叉分子束装置中, 研究氧原子和CF2=CFCl, CF2=CFBr,CF2=CH2的反应。在O(^3p)和CF2=CFBr(或CF2=CFBr)反应中, 首次观察到反应生成的CF2(^3B1)的发射光谱, 而在O与CF2=CH2反应中, 用激光诱导荧光方法检测到CFH卡宾, 确定了在此反应中CFH卡宾的生成, 这一结果未见文献报道。并根据这些结果, 分析和讨论了在这些反应中, 生成CF2(^3B1)和CHF卡宾的机理。 相似文献
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A new bis(carbene) ligand architecture has been developed and was evaluated in the Suzuki-Miyaura cross-coupling reaction of various aryl halides with phenylboronic acid. Several new bis(carbene) ligands were tested in different carbene:Pd ratios. Pd(OAc)(2) and Pd(2)(dba)(3) were compared for efficiency as a Pd source. It was found that the Pd(OAc)(2)/bis(carbene) system formed a catalyst for the activation of chlorobenzene. [reaction: see text] 相似文献
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The detailed reaction pathways for the ammonium cyanate transformation into urea (W?hler's reaction) in the gas phase, in solution, and in the solid state have exhaustively been explored by means of first-principles quantum chemical calculations at the B3LYP level of theory using the 6-31G(d,p) basis set. This serendipitous synthesis of urea is predicted to proceed in two steps; the first step involves the decomposition of the ammonium cyanate to ammonia and isocyanic or cyanic acid, and the second one, which is the main reaction step (and probably the rate-determining step), involves the interaction of NH(3) with either isocyanic or cyanic acid. Several alternative pathways were envisaged for the main reaction step of W?hler's reaction in a vacuum involving the formation of "four-center" transition states. Modeling W?hler's reaction in aqueous solution and in the solid state, it was found that the addition of NH(3) to both acids is assisted (autocatalyzed) by the active participation of extra H(2)O and/or NH(3) molecules, through a preassociative, cooperative, and hydrogen-transfer relay mechanism involving the formation of "six-center" or even "eight-center" transition states. The most energetically economic path of the rate-determining step of W?hler's reaction is that of the addition of NH(3) to the C=N double bond of isocyanic acid, directly affording urea. An alternative pathway corresponding to the anti-addition of ammonia to the Ctbd1;N triple bond of cyanic acid, yielding urea's tautomer HN=C(OH)NH(2), seems to be another possibility. In the last case, urea is formed through a prototropic tautomerization of its enolic form. The energies of the reactants, products, and all intermediates along with the barrier heights for each reaction path have been calculated at the B3LYP/6-31G(d,p) level of theory. The geometry optimization and characterization of all of the stationary points found on the potential energy hypersurfaces was performed at the same level of theory. 相似文献
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(R)-螺[4,5]癸-2,7-二酮的合成 总被引:3,自引:1,他引:3
从环己烯酮出发,经手性催化的Michael加成反应,Wolff重排反应延长碳链, 再利用重氮化合物的C-H插入反应,以8步反应28.5%的总收率合成了手性β,β '-螺二酮.在合成路线中手性中心的构型保持不变.在最后的检测中未发现另一对 映体,开始产生的手性中心在合成过程没有消旋化。 相似文献
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Reaction pathway and stereoselectivity of asymmetric synthesis of chrysanthemate with the aratani C1-symmetric salicylaldimine-copper catalyst 总被引:2,自引:0,他引:2
The reaction pathway and the mechanism of asymmetric induction in the synthesis of (+)-trans-(1R,3R)-chrysanthemic acid methyl ester from methyl diazoacetate and 2,5-dimethyl-2,4-hexadiene in the presence of a C(1)-chiral salicylaldimine Cu(I) complex has been probed with the aid of hybrid density functional calculations. The key finding is that the alkoxycarbonyl carbene complex intermediate is intrinsically chiral and that the intramolecular hydrogen bonding in the carbene complex transmits the chirality information from the side chain to the carbene complex. Molecular orbital backgrounds of the structure of the carbene complex and the transition state of the cyclopropanation have been elucidated. 相似文献
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Polycyanurates (poly(2,4,6-trisaroxy-1,3,5-triazines)) are built up through a step-growth polycyclotrimerization of difunctional aromatic cyanic acid esters and form an ideally trifunctional randomly branched network, where all initial cyanato groups are linked with the triazine branching units at full conversion. Results on modifications of the high network density of pure polycyanurates are reported for three types of comonomers: monofunctional cyanic acid esters, difunctional phenols and difunctional aromatic glycidyl ethers. Using the coreaction of mono- and difunctional aromatic cyanic acid esters, additional chain segments, dangling ends and low molecular weight compounds are built, the fractions of which are dependent on the initial admixture of the monofunctional compound and its relative reactivity. Therefore, the critical conversion at the gel point is shifted to higher values and the network density at full conversion decreases. The abstraction of phenols from intermediately formed iminocarbonic ester structures is utilized for the modification of the polycyanurate network through the coreaction of difunctional aromatic cyanic acid esters with phenols. It was found that the critical conversion and the network structure are dependent on all the initial amount of phenols, their reactivity and functionality. The modification with the help of glycidyl ethers is characterized by an insertion of the oxirane ring into the cyanurate and the succeeding reactions into isocyanurates and oxazolidinones. Depending on the initial mixture and the reaction conditions, a large spectrum of chemical and topological network structures can be obtained, what is demonstrated by both experimental and theoretical investigations. 相似文献
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Dmiry A. Rud Natalia S. Kushakova Alexey V. Shapovalov Alexander V. Naumkin Irina V. Zhidkova Irina A. Khotina 《Macromolecular Symposia》2010,296(1):388-391
Polyphenylenes supported N-heterocyclic carbene Pd-complexes were synthesized for catalysis of cross-coupling Suzuki-Miyaura reactions. Starting polyphenylenes were prepared by cyclocondensation reaction of diacetylaromatic with monoacetylaromatic compounds. N-metylimidazole has been involved to the polymer through the mono-functional acetyl monomer, in which in p-position to acetyl group the group of haloalkyl was situated, and haloalkyl group interacted with N-methylimidazole. N-heterocyclic carbene complexes of Pd were synthesized usually by the reaction of imidazolium salts with the salts of transition metals in the presence of a base, obtaining the complex (N-heterocyclic carbene)2PdX2. The catalysis reaction was carried out between arylhalides (iodo- or bromobenzene) and phenylboronic acid with the presence of 1 mol% of Pd. The yields of biphenyl are from 70 to 95%, which is comparable with homogeneous catalysis. 相似文献