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71.
The different mechanisms, rotation, inversion, or intermediate mechanism, by which occur the topomerization of imine systems R2 CN X have been studied by applying ab initio, B3LYP, and MP2 methods. The effect of a wide variety of substituents R and X on the isomerization pathway have been examined by computing fully optimized structures of the ground and transition states (136 isomers belonging to different imine families were studied and more than 300 transition structures were determined at various levels of theory). Energy barriers have been also obtained and it was found that the groups R and X have a strong influence on the type of mechanism involved and the activation energies. Thus, and depending on the type of substituents, transition state structures related to the following kinds of processes were found: pure inversion, intermediate mechanisms, rotation, and enhanced rotation (hyper‐rotation). In turn, the corresponding activation energies range between very low (<10 kcal/mol) and extremely high (> 70 kcal/mol) values. A simple index that allows us to quantify the percentage of inversion or rotation mechanism is proposed. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010 相似文献
72.
Theoretical methods have been employed to investigate the structural, spectroscopic and energetic properties of difluoro(germylthio)phosphine in the Cs symmetry in the gas phase. The levels of theory used are MP2 and DFT/B3LYP and the basis set used for all atoms is 6-311G(d,p). The computed structural parameters, namely, bond lengths and bond angles and spectroscopic parameters, namely, infrared frequencies, Raman activities and NMR chemical shifts have been compared with experimental data reported in literature. The structure of this compound has been analysed using natural bond orbital approach. Both the ab initio methods perform satisfactorily when the predicted and experimental parameters are compared. We have extended this study, using the same methods and basis set, to the selenium analogue, namely, difluoro(germylseleno)phosphine for which literature is elusive. The MP2/6-311G(d,p) geometrical parameters for difluoro(germylseleno)phosphine are: r(P–Se) = 2.270, r(Ge-Se) = 2.386, r(P–F) = 1.604, r(Ge–H) = 1.530 Å, ∠(Ge–Se–P) = 91.4, ∠(F–P–F) = 96.7, ∠(Se–P–F) = 99.9 and ∠(Se–Ge–H) = 109.5°. Apart from these, we have also studied the energetic parameters for their synthesis. The results indicate that formation of the sulphur-containing compound is favoured thermodynamically. 相似文献
73.
The wave functions for calculating gas phase 19F chemical shifts were optimally selected using the factorial design as a multivariate technique. The effects of electron correlation, triple-ξ valance shell, diffuse function, and polarization function on calculated 19F chemical shifts were discussed. It is shown that of the four factors, electron correlation and the polarization functions affect the results significantly. B3LYP/6-31 + G(df,p) wave functions have been proposed as the best and the most efficient level of theory for calculating 19F chemical shifts. An additional series of fluoro compounds were used as a test set and their predicted 19F chemical shifts values confirmed the validity of the approaches. 相似文献
74.
Geometry optimisation and metal ion affinities (MIAs) of the binding configurations of Be2+, Mg2+ and Ca2+ to L ‐proline were calculated using the hybrid Density Functional Theory (DFT‐B3LYP) and second order Møllet?Plesset perturbation theory (MP2) methods. Be2+ was found to bind preferentially in a charge transfer type arrangement through the carbonyl oxygen (? C?O) and the lone pair of the imino‐group nitrogen atom (? NH? ). On the contrary Mg2+ and Ca2+ were found to prefer binding in a bi‐dentate manner through the carboxylate group of L ‐proline (OCO) in a zwitterion form. The main types of interactions found to influence the binding preference of M2+ ions to L ‐proline were (i) charge transfer in the case of Be2+ ions and (ii) electrostatic interactions in the case of Mg2+ and Ca2+ ions. Inspection of the IR stretching of the N? H and the O? H groups of L ‐proline with M2+ ions in a chelating configuration (to both O and N atoms) indicated a considerable shift to higher frequency with decreasing MIA. On the other hand, the MIA for the zwitterion L ‐proline with M2+ tracks the reciprocal distance of the M2+? OCO bond further confirming that the nature of the bond is mainly electrostatic. Comparison with other molecules containing the carboxylic function is also included in order to gain more insight on the types of interaction of this amino acid with metal ions in general. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
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77.
《电子技术与软件工程》2017,(8)
火电厂快速减负荷(fast cutback,FCB)功能是大型机组不可缺少的重要安全保障,通过对波黑斯坦纳瑞300MW燃煤机组FCB功能控制要求的分析,对DEH控制系统的改进。 相似文献
78.
18Ni(300)钢高速干滑动摩擦磨损特性研究 总被引:1,自引:0,他引:1
利用销盘高速干滑动摩擦磨损试验机,对18Ni(300)马氏体时效钢的摩擦磨损性能进行了研究,应用JSM-6390A型扫描电子显微镜和X-衍射方法对摩擦磨损表面进行观察,表征其摩擦表面的微观形貌、摩擦磨损的磨屑以及由于摩擦产热而引起的氧化物,进而推断出磨损机制.结果表明:摩擦副的摩擦系数随载荷和速度的增加而下降;随着转速和载荷的增加,销表面氧化物逐渐由FeO转变为Fe_3O_4,其磨损机制由黏着磨损转变为严重的氧化磨损. 相似文献
79.
Ab initio electronic structure calculations using MP2 wavefunctions have been used to investigate a reaction path for the
hydrosilation reaction catalyzed by divalent titanium [modeled by TiH2, TiCl2, and Ti(C5H5)2]. Optimized structures and energies are presented. All model reactions predict a barrierless reaction path compared to a
barrier of 78 kcal/mol for the uncatalyzed reaction.
Received: 11 August 1998 / Accepted: 3 September 1998 / Published online: 23 February 1999 相似文献
80.
Jonas Boström Valera Veryazov Francesco Aquilante Thomas Bondo Pedersen Roland Lindh 《International journal of quantum chemistry》2014,114(5):321-327
An algorithm for computing analytical gradients of the second‐order Møller–Plesset (MP2) energy using density fitting (DF) is presented. The algorithm assumes that the underlying canonical Hartree–Fock reference is obtained with the same auxiliary basis set, which we obtain by Cholesky decomposition (CD) of atomic electron repulsion integrals. CD is also used for the negative semidefinite MP2 amplitude matrix. Test calculations on the weakly interacting dimers of the S22 test set (Jure?ka et al., Phys. Chem. Chem. Phys. 2006, 8, 1985) show that the geometry errors due to the auxiliary basis set are negligible. With double‐zeta basis sets, the error due to the DF approximation in intermolecular bond lengths is better than 0.1 pm. The computational time is typically reduced by a factor of 6–7. © 2013 Wiley Periodicals, Inc. 相似文献