Synthesis and Isomerization of the 2-Methyl Enal Fragment of Acyclic Precursors to 9,11-Diene Analogs of Epothilones

Russian Journal of Organic Chemistry - Yamaguchi esterification of (2Z,5S,6E)-5-(hydroxymethyl)-2,6-dimethyl-7-(2-methyl-1,3-thiazol-4-yl)hepta-2,6-dienal with...     

甲基硅乙烯异构化反应的理论研究 用从头算结果讨论其热力学、动力学性质

The titled isomerizaton of methylsilene has been studied at ab initio level. Theharmonic vibrational frequencies of reactant, product and transition state, the barrier energy, reaction heat, equilibrium constant and rate constant are calculated. The results indicate that this reaction is exothermic, spontaneous and high temperature above 900 K is favourable for the isomerization. The prediction is in agreement with experiment.     

硅乙烯异构化反应的理论研究——从头算水平上的热力学、动力学分析

据报道,含硅碳双键的化合物已能制备,但它在通常条件下不稳定,易于发生加成、异构化反应,研究最多的两个异构化反应是:     

硝基胍H迁移异构化反应动力学的从头计算研究

Theoretical studies on the α- and β-forms nitroguanidine were carried out using ab initio theoretical methods, at the MP2/6-31G(d,p) level. The predicted geometrical parameters were in good agreement with the available theoretical values, which calculated by other author. The three C-N bond lengths in α-form nitroguanidine were different, the longest bond length was 1.430 A, the shortest was 1.283 A. But they were almost similar in β-form, the longest was 1.375 A, the shortest was 1.322 A. Therefore there were conjugative effects in β-form but not in α-form. The calculated results also show that the β-form is stable with respect to the α-form from energetically, lower 28.16 kJ/mol corrected with zero point vibrational energy. The transition-state for the unimolecular isomerization was conformed by the IRC calculation. The calculated energy barrier for the direct intramolecular hydrogen atom transfer isomerization process was 132.95 kJ/mol. The isomerization reaction, exothermal reaction, is a typical intramolecular hydrogen atom synfacial transfer reaction. Rate constants of the isomerization reaction were evaluated within the temperature range of 200-1773 K by the classical transition state theory. The rate constant was 1.99×10-11 s-1 and the equilibrium constant was 1.00×105 at 298 K. With the temperature increasing, the equilibrium value decayed and the reaction process was more difficult.     

A Theoretical Study on the Isomerization of HSOF System

1 INTRODUCTION The chemistry of atmospheric sulfur has beenlong studied due to its significant role in environmen-tal problems, such as acid rain, ozone and chemicalair pollution. To solve such problems, further know-ledge of the underlying processes involved in the at-mospheric sulfur cycle is necessary[1]. Moreover, de-tection of many sulfur-containing inorganic mole-cules in interstellar clouds has been reported. Thereactions of SO , an abundant ubiquitous interstellarion, with man…     

N-甲硝胺异构化和分解反应机理和动力学的理论研究

The complex potential energy surface and reaction mechanisms for the unimolecular isomerization and decomposition of methyl-nitramine (CH3NHNO2) were theoretically probed at the QCISD(T)/6-311+G*//B3LYP/6-311+G* level of theory. The results demonstrated that there are four low-lying energy channels: (i) the NN bond fission pathway; (ii) a sequence of isomerization reactions via CH3NN(OH)O; (IS2a); (iii) the HONO elimination pathway; (iv) the isomerization and the dissociation reactions via CH3NHONO (IS3). The rate constants of each initial step (rate-determining step) for these channels were calculated using the canonical transition state theory. The Arrhenius expressions of the channels over the temperature range 298-2000 K are k6(T)=1014:8e-46:0=RT , k7(T)=1013:7e-42:1=RT , k8(T)=1013:6e-51:8=RT and k9(T)=1015:6e-54:3=RT s-1, respectively. The calculated overall rate constants is 6.9￡10-4 at 543 K, which is in good agreement with the experimental data. Based on the analysis of the rate constants, the dominant pathway is the isomerization reaction to form CH3NN(OH)O at low temperatures, while the NN bond fission and the isomerization reaction to produce CH3NHONO are expected to be competitive with the isomerization reaction to form CH3NN(OH)O at high temperatures.     

Kinetic Study on the Isomerization of Perindopril by HPLC

The isomerization of perindopril has been investigated using dynamics chromatography and an unified equation introduced by Trapp that was based on stochastic and theoretical plate models to determine the energies. The isomerization rate constants and Gibbs activation energies of isomerization are directly calculated from chromatographic peak parameters, i.e., retention times of the inter-converting species, peak width at half height, and relative plateau height. From the rate constant \( k_{1}^{ue} (T) \), measured at variable temperatures, the kinetic eyring activation parameters ΔG ^#, ΔH ^# and ΔS ^# of isomerization of perindopril were obtained. By variation of the flow rate of the mobile phase, the expected independence of the isomerization barrier from the chromatographic time scale was demonstrated for the first time. The relationships between peak shape and chromatographic conditions, such as flow rate, temperature, pH, organic modifier, and β-cyclodextrin, such as an additive, were investigated. In addition, an NMR investigation on perindopril was described.

     

过亚硝酸异构化反应机理的密度泛函理论研究

用密度泛函理论方法研究了过亚硝酸在水溶液中的异构化反应机理。在 B3LYP/6-31G水平基础上用梯度解析技术全自由度优化了反应物、产物和反应途径 中的中间产物及过渡态的几何构型，并通过振动频率分析加以确认，进行了内禀反 应坐标计算，确定了该反应的可能通道。结果表明：该反应为多通道强放热反应， 其中以羟基直接转移途经能垒最小，绝对反应速率常数值最大，因此，推测该通道 为主要的反应通道。     

Synthesis and Study of Equilenin Derivatives and Modified Analogs

Modified equilenin analogs were synthesized with a view to examine the relation between the structure and biological properties of steroid estrogens. The ¹H and ¹³C NMR signals of six estra-1,3,5,7,9-pentaenes were completely assigned using homo- and heteronuclear correlation NMR spectroscopy. The structure of equilenin methyl ester was determined by X-ray analysis. Among the synthesized steroids, compounds were found which exhibit hypocholesterinemic activity with no uterotropic and hypertriglyceridemic effects.     

Isomerization of alkyldiacetylenes

Summary The easy isomerization of monoalkyldiacetylenes to methylalkyldiacetylenes under the influence of an alcoholic solution of alkali was established.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 1659–1660, September, 1965     

Isomerization of monohydroperfluoroalkenes

Isomerization of monohydroperfluoro-1-alkenes HC(CF₂)_nCF=CF₂ (n = 2 to 8) catalyzed by Lewis bases or acids (CsF, KHF₂, and SbF₅) under conditions of thermodynamic control affords equilibrium mixtures of all of the possible isomers resulting from migration of the double bond along the carbon chain. Under conditions of kinetic control, isomerization through the action of SbF₅ gives -H-perfluoro-2-alkenes. The substantially higher proportion ofcis-isomers in the resulting monohydroperfluoroalkenes than in their perfluorinated analogs has been attributed to the effect of an intramolecular hydrogen bond.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1614–1619, September, 1994.     

关于二氟乙炔的异构化反应的量子化学研究

用ａｂ ｉｎｉｔｉｏｎ方法讨论了Ｆ２Ｃ２的异构化反应机理，用ＨＦ／６－３１Ｇ和ＭＰ２／６－３１Ｇ优化Ｆ２ＣＣ和二氟乙炔（ＦＣ＝ＣＦ）的几何构型，并得到反庆Ｆ２ＣＣ＿ＦＣＣＦ的过渡态（ＦＣ（Ｆ）Ｃ）。文中用内禀反应坐方法做反应路径解析，二氟乙炔是二氟丙二烯酮分解反应的产物，用从头算方法优化二氟丙二烯酮并在Ｍｕｌｌｉｋｅｎ集居分析中，发现Ｆ２Ｃ＝Ｃ＝Ｃ＝Ｏ在分解反庆中先产生中间产Ｆ２ＣＣ，之后经过过渡     

B_4O分子异构化稳定性的理论研究

采用CCSD(T)/6-311+G(2df)//B3LYP/6-311+G(d)方法, 系统研究了B₄O体系各个异构体的结构和能量, 以及重要异构体的解离和异构化稳定性. 结果表明, 单态平面三角形含-BO单元的异构体cB₃-BO ¹1能量最低, 其次是带状的异构体B₄O ¹2(10.9 kJ/mol), 并且¹1和¹2结构都具有良好的动力学稳定性. 因此对于B₄O体系, ¹1和¹2都是有可能存在的. 而文献报道的三态直线型结构BBBBO(146.0 kJ/mol)的能量比异构体¹1和¹2高得多.     

Study of the Mechanism of Hexane Isomerization under Micropulse Conditions

We have developed a highly informative micropulse method for isomerization of n-hexane. We have found that the primary reaction products on Pd/HM, Pd/HY, and Pd/HTsVM [analog of HZSM] catalysts are only 2- and 3-methylpentanes. We propose mechanisms for their formation. The reaction is considered to be unimolecular.     

ClONO2异构化反应和分解反应的理论研究

The potential energy surface for the decomposition and isomerization of Chlorine Nitrate（ClONO2）is calculated using the G3 theory. Geometries of related species are optimized at the MP2（ full）/6-31+G（d）and B3LYP/6-31+G（d）level. Vibrational frequencies and IR intensities of ClONO2 have been calculated at the same level. Obtained geometries and vibrational frequencies as well as IR intensities for ClONO2 are in good agreement with experimental values. A new stable stereoisomer is verified by CCSD（T）and QCISD（T）methods at 6-311G （d）basis set. Calculated geometries using above methods for this stereoisomer are in accord with each other. The calculated reaction heat of ClONO2 are also in good agreement with the available data in the literature. Among these reactions of ClONO2,the stereoisomer reaction is the hardest one. The barrier height for this reaction is 481.52 kJ/mol relative to ClONO2 and the reaction is endothermic by 299.85 kJ/mol. On the other hand,among these unimolecular reactions of ClONO2,the decomposition reaction of NO2+ClO is the easiest one. These results indicate that ClONO2 is very stable.