共查询到20条相似文献,搜索用时 10 毫秒
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Jairo Quijano Jorge David Claudia Snchez Elizabeth Rincon Doris Guerra Luis A. Len Rafael Notario Jos L. Abboud 《Journal of Molecular Structure》2002,580(1-3):201-205
Thermolysis studies of β-hydroxyolefins in gas phase were realized using ab initio MP2 and DFT methods at the 6-31G* levels to explore the possibility of determining a possible concerted process with a six-membered cyclic transition state (TS). Vibrational frequency calculations were carried out in order to confirm the stationary states, including TS structures. IRC calculations have been performed in all cases in order to verify that localized TS structures connect with the corresponding minimum stationary points associated with the reactant and products. With the aim of corroborating the postulated mechanism in the experimental study, we present a theoretical study in order to calculate the rate constants and the activation parameters. The results obtained are in accordance with the experimental conclusions. 相似文献
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采用自洽场分子轨道UHF/6-31G**从头算法,研究了1,2-C4H6→2-C4H6异构化反应机理,优化了基态势能面上反应物、过渡态、中间体和产物的几何构型,并对各驻点能量进行了零点能校准.结果表明该反应经历一个1-甲基环丙烯生成产物比经两步氢迁移反应历程更易发生. 相似文献
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The dynamics of vinylidene-acetylene isomerization has been studied quantum mechanically, based on a new ab initio calculated
potential energy surface (PES). The grid underlying the PES and the dynamic treatment rest on planar 4-atom Jacobi-like coordinates.
Three degrees of freedom, the C-C bond length and the two Jacobi-like angles are treated explicitly, while the two other coordinates
relating to the C-H bond lengths have been optimized in the ab initio treatment. The energies of the resulting 3D grid have
been computed with the CCSD(T) method, using a cc-pVTZ basis set, while selected stationary points have been characterized
at a higher level of theory. The subsequent dynamic treatment reproduces very satisfactorily the experimental photodetachment
spectrum of Lineberger and coworkers. Preliminary results are also reported for the lifetime of vinylidene.
Received: 5 June 1998/Accepted: 23 July 1998 / Published online: 9 October 1998 相似文献
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We present a theoretical calculation of trinem antibiotic sanfetrinem GV104326 and its cis-isomer of proton in β-lactam ring and methoxy inversion isomer. Ab initio Hartree Fock method is employed to calculate the geometry optimization; optimized parameters, bond lengths, bond angles and dihedral angles of isomers. We also calculated the vibrational frequencies, the IR intensities, the Raman activities and the thermochemical parameters. Mulliken population analysis is used to compare bond strength of an active site. These results are compared with available experimental data and other related theoretical calculations. The calculated IR spectra are in good agreement with experiments. Calculated geometrical and conformational structures of sanfetrinem and its isomers support the previous study of the geometrical requirements for the antibacterial activities. The significance of the rotational conformation of the carboxyl group to chemical reactivities is discussed. 相似文献
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Errol Lewars 《Journal of Molecular Structure》1996,360(1-3):67-80
Ab initio calculations have been performed on benzooxirene, the corresponding oxo carbene (“ketocarbene”), and the transition state linking the two. At the highest level used, QCISD(T)/6-31G*//MP2(FULL)/6-1G* with MP2(FULL)/ 6-31G* zero point energy corrections, the relative energies of the oxirene, the transition state and the carbene are 0, 24.6, and −17.8 kJ mol−1. Correlation energy effects are very important in this system: at the QCISD(T) level the oxirene lies above the carbene, as at the MP4 and HF levels, but at the MP2 level the ordering is reversed. Benzooxirene is probably slightly nonplanar: the HF/6-31G* geometry is C2v but the MP2(Fermi contact)/6-31G* geometry is Cs with a 6-/3-ring coplanarity deviation of about 6.9 °, although in the MP2(FULL)/6-31G* geometry this is reduced to about 3.1 °. 相似文献
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V. A. Dorokhov A. V. Komkov A. M. Sakharo V. S. Bogdanov 《Russian Chemical Bulletin》1996,45(1):168-170
A method hxsynthesizing 3-acetyl-2-amino-4-pyyridone has been suggested. The synthesis involves the condensation of dimethylformamide dimethylacetal at the NH2 group of diphenylboron chelate diacetylketene aminal followed by its intramolecular cyclization under the action of NaOMe in MeOH.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 177–179. January, 1996. 相似文献
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使用CCSD(T)/aug-cc-pVTZ从头计算方法,对[He3H]+分子的一些特殊构型的电子基态势能进行扫描,并以此为基础对三体相互作用势在惰性气体质子簇中的影响进行了讨论.结果表明即使在这样一个简单的体系中三体相互作用的影响都是不能忽略的.另一方面,在[He3H]+分子稳定构型附近仅将势能展开至三体相互作用项便可提供较精确的相互作用信息,但在强排斥区域更高阶作用的影响变得越来越突出.本文同时讨论了[He4H]+的稳态结构. [He3H]+与[He4H]+的稳态结构表明,[HenH]+簇中存在着一个[He2H]+核. 相似文献
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在B3LYP/6-31+G(d,p)理论水平下采用基于波恩-奥本海默近似的从头算分子动力学方法重新研究了O-与CH3F反应经抽氢生成OH-和生成H2O的两条产物通道.反应轨线从反应初始过渡态开始,采用300K时的热取样确定初始条件,同时为对比不同的初始碰撞平动能条件下产物通道的变化,分别限定过渡矢量上的能量为2.1、36.8及62.8kJ·mol-1进行轨线计算,所有轨线计算的结果表明抽氢生成OH-的过程始终为主要的产物通道.我们的计算不仅进一步证实了以往实验的结论,而且描绘了抽氢生成OH-和生成H2O这两个产物通道在反应出口势能面上的动态反应路径,更为深刻地揭示了该反应的微观机理. 相似文献
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在MP2/6-311+ +G(3d,3p)电子相关校正水平上,对CH3F二聚体可能存在的几何构型进行全自由度能量梯度优化和频率验证,发现3种势能面上有极小点的构型.进一步在高级电子相关校正的MP4S-DTQ、CCSD(T)/6-311+ +G(3df,3pd)方法水平上,对其中总能量最小的构型进行精确计算,得到二聚体的结合能为-9.707kJ/mol.研究结果支持了由光谱实验结果推测的构型,解释了CH3F二聚体的谐振频率的多样性. 相似文献
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The geometries of the dipeptides
-Pro-
-Ala,
-Pro-
-Ala and
-Pro-Gly were investigated by a grid scan ab initio calculation. The 6-31G basis set was used to estimate the effect of the alanyl side-chain on the conformation of the peptide backbone and to provide a computational basis for the interpretation of known physical-chemical properties of larger peptides that contain these dipeptides. These calculations furnish a direct quantum mechanical assessment of the energetic consequences of a methyl side-chain in the i + 2 position of a turn. The results of the calculation support the current view that the presence of a
-Ala residue in the i + 2 position favors a type II β-turn over a type I β-turn conformation, while
-Ala has the opposite effect. Total and relative energies for all the optimized conformations identified by the grid search are given and geometric parameters (bond lengths, bond angles and dihedral angles) and net atomic charges have been calculated. 相似文献
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用abinitio方法研究2,4-二甲基-1,3-戊二烯各种构象异构体的结构,找到s-trans和s-cis两种稳定构象,且s-trans更稳定.对稳定构象的几何结构、电荷分布进行了研究,讨论了不同的电子基组对优化几何的影响,并计算了稳定构象的热力学常数,与实验结果进行了比较. 相似文献
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利用双水平直接动力学方法对反应CH3SH+H的微观机理和动力学性质进行了理论研究.对于此反应的三个反应通道,即—SH和—CH3基团上的两个氢提取通道及一个取代通道,在MP2/6-311+G(d,p)水平上优化得到了各稳定点的结构及振动频率,并在G3(MP2)水平上进行了单点能量计算以获得更精确的能量信息;在此基础上运用结合小曲率隧道效应校正的变分过渡态理论(CVT/SCT)计算了各反应通道在220-1000 K温度区间的速率常数.计算结果表明提取—SH基团上H的反应通道R1在整个反应温度区间都是主要通道,而随着温度的升高,低温下的次要反应通道——取代通道R3变得越来越重要,并且在高温下将成为一个竞争的反应通道;提取—CH3基团上H的反应通道(R2)由于具有较高的反应能垒,因而,其对总反应速率常数的贡献可以忽略.计算得到的总反应速率常数与已有的实验值符合得很好,进而我们预测了该反应在220-1000 K温度范围内速率常数的表达式为:k=5.00×10-18T2.39exp(-119.81/T),为将来的实验研究提供参考. 相似文献
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Bairong Shen Kangnian Fan Wenning Wang Jingfa Deng 《Journal of Molecular Structure》1999,469(1-3):157-161
We present an ab initio study on the adsorption and oxidation of HCHO on the Ag2 dimer. HCHO is found to weakly adsorb on the neutral Ag2 cluster and the adsorption energy increases when the Ag2 cluster is positively charged. The adsorption of HCHO on Ag2 is promoted by pre-adsorbed OH species while coadsorbed H has no effect. The formation of η2-methylendioxy is inhibited if the Ag2 cluster is positively and properly charged, which enhance the selectivity of the partial oxidation of methanol. These results provide insight into the reaction mechanism of HCHO on silver surfaces and may guide the design of novel catalysts. 相似文献
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The potential energy, dipole, quadrupole and octopole moments and dipole polarisabilities have been calculated at CASSCF level for the ground X1Σ+ state of the PO+ molecular ion as a function of internuclear distance. Most of the electrical properties have not previously been calculated and show rapid variations around 5 a.u. due to a perturbation. The calculated vibrational frequency of 1410.4 cm−1 and the integrated IR absorption intensity of 984 cm2 mol−1 should lead towards the first observation of the vibrational spectrum. 相似文献
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InSb的Li替位形成能的从头计算 总被引:1,自引:0,他引:1
采用基于平面波展开的第一原理赝势法计算了锑化铟在锂替位到铟位置时的各种情况下的形成能与电子结构,讨论了锂替位的体积变化,电荷分布、能带结构及电子态密度等性质.结果表明,对于闪锌矿结构的InSb,锂的各种替位形成能大致在每个锂原子-2.2eV左右.该结果表明,不可能在嵌入初期Li插入到间隙位置之前发生替位反应,与实验结果一致. 相似文献
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The parametric method three (PM3) has been used to predict the optimized geometries of the transition state involved in the
tautomerization process of 2-pyridone, its 6-chloro derivative and carbostyril. The estimated activation energies for the
hydrogen shift of the three compounds are 41.2, 41.3 and 44.9 kcal mol−1, respectively. The effect of polar solvents on the tautomerization process has been discussed by consideration of the calculated
dipole moments for the reactant, the transition state and the product. Examination of OH and NH bond orders reveals a point
of inflection in each case in the vicinity of the transition state. 相似文献