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991.
A. L. Chistyakov I. V. Stankevich N. P. Gambaryan I. A. Tikhonova V. B. Shur 《Russian Chemical Bulletin》1995,44(6):997-1004
Geometries and electronic structures of the complexes of halide anions with cyclic trimerico-phenylenemercury, (o-C6H4Hg)3, perfluoro-o-phenylenemercury, (o-C6F4Hg)3, vinylenemercury, (C2H2Hg)3, and perfluorovinylenemercury, (C2F2Hg)3, were modelled by the MNDO method. Calculations were performed for [L-X]– semisandwich complexes, [X-L-X]2– bipyramidal complexes, and [L-X-L]– sandwich complexes (where X=Hal,L is a mercury-containing macrocycle). Based on the results of calculations, we concluded that it was advantageous to describe the chemical bonding between halide anions and mercury-containing macrocycles in terms of generalized chemical bonds, which were successfully used for -complexes of transition metals. In the [L-X]– semisandwich complexes, the halide anion and the metallacycle are involved in the formation of three generalized chemical bonds: one headlight-shaped -bond and two two-lobe -bonds. In the [X-L-X]2– bipyramidal complexes, each halide anion forms three generalized chemical bonds with the macrocycle. It is possible because the macrocycleL has unoccupied molecular orbitals suitable for the formation of such bonds; these MOs consist mainly of the orbitals of mercury atoms directed toward both the upper and lower halogen atoms. In the [L-X-L]– sandwich complexes, the halide anion cannot be bonded to each ringvia three bonds, and, hence, an unsymmetrical structure is formed, in which the rings are located at different distances from the central atom: the [L-X]– semisandwich complex solvated by macrocycleL.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1035–1042, June, 1995.The authors are grateful to V. I. Faustov for valuable remarks.This work was supported by the Russian Foundation for Basic Research (Project No. 93-03-18342). 相似文献
992.
Josef Scharf Karl Schlögl Michael Widhalm Johann Lex Werner Tückmantel Emanuel Vogel Franz Pertlik 《Monatshefte für Chemie / Chemical Monthly》1986,117(2):255-267
2,7-Dibromo-1,6-methano[10]anulene (3) and 2,9-Dibromo-syn-1,6:8,13-diimino[14]anulene (9) were quantitatively separated into their enantiomers by chromatography on triacetylcellulose (TAC) in ethanol. X-ray structure analysis (Bijvoet technique) established the chiralities (+)(R)-3 and (+)(S)-9 for the dextrorotatory enantiomers.Comparison of the CD spectra allowed the configurational assignment to further optically active [10] and [14] anulenes which were also accessible by chromatography onTAC. Conversion of (+)(R)-2-bromo-1,6-methano[10]anulene (2) into the corresponding methylester (–)-4 confirmed its previously proposed chirality (–)(R).2,7-Dibromo-1,6-oxido[10]anulene (7) and 2,9-dibromo-syn-diimino[14]anulene (9) are in contrast to the 2,9-dibromo-syn-dioxido[14]anulene (10) optically stable until 250°C. Consequently their inversion barriers are higher than 42 kcal (176 kJ) mol–1.The CD spectra of mono and disubstituted anulenes (with C1 and C2 symmetry, resp.) are compared: For the [10]anulenes theCotton effect around 330 nm seems to be specific for their configuration with a positive effect indicating (S)-chirality and vice versa. Some regularities concerning the chromatographic resolutions are discussed.
Stereochemie planar chialer Verbindungen, 10. Mitt.: Röntgenkristallstruktur und absolute Chiralität überbrückter [10]- und [14] Anulene
Zusammenfassung 2,7-Dibrom-1,6-methano[10]anulen (3) und 2,9-Dibrom-syn-1,6:8,13-diimino[14]anulen (9) wurden durch Chromatographie an Triacetylcellulose (TAC) in Ethanol quantitativ in ihre Enantiomeren getrennt. Röntgenstruktur-analyse (Bijvoet-Technik) bewies für die rechtsdrehenden Enantiomeren die Chiralität (+)(R)-3 bzw. (+)(S)-9.Ein Vergleich der CD-Spektren ermöglichte die Konfigurationszuordnung weiterer optisch aktiver [10]- und [14]Anulene, die gleichfalls durch Chromato-graphie anTAC erhalten worden waren. Umwandlung von (+)(R)-2-Brom-1,6-methano[10]anulen (2) in den entsprechenden Methylester (–)-4 bestätigte dessen schon früher vorgeschlagene Chiralität (–)(R).Dibrom-1,6-oxido[10]anulen (7) und Dibrom-diimino[14]anulen (9) sind im Gegensatz zum Dioxido[14]anulen (10) bis 250°C optisch stabil. Ihre Inver-sionsbarrieren liegen somit über 42 kcal (176kJ) mol–1.Die CD-Spektren von mono- und disubstituierten Anulenen (mit C1 bzw. C2-Symmetrie) werden verglichen: Für die [10]Anulene scheint derCottoneffekt um 330 nm konfigurationsspezifisch zu sein, wobei ein positiver Effekt (S)-Chiralität anzeigt — und vice versa. Einige Regelmäßigkeiten bezüglich der chromatographischen Enantiomerentrennung werden diskutiert.相似文献
993.
994.
用X_α方法对CH_4在Ni(Ⅲ)表面吸附解离反应的理论研究马晨生,马理,杨忠志(吉林大学理论化学研究所,长春,130023)关键词CH_4/Ni(Ⅲ)吸附体系,原子簇模型,CH_4/Mi_7,MS-X_α-SCF方法甲烷在Ni表面的催化重整反应在工业和国... 相似文献
995.
DFT method (B3LYP) with 6-31G* basis set was utilized in the computation of a fully optimized structure, net atomic charges and spin densities of the intermediate of cytochrome P-450-oxoiron(IV) porphyrin cation radical, compound I – in the presence of axial ligand such as thiolate (SMe−) imidazole (IM), phenoxide (OPh−), methoxide (OMe−) and chloride (Cl−). The results show doublet states in compound I are about 2–4 kcal/mol more stable than quartet states for all aforementioned ligands, and the doublet state is the ground state in all cases. However, electron donor ability of the ligands are in the order of SMe− > IM > OMe− > OPh− > Cl−. Also the active oxidant intermediate of cytochrome P-450 between different mesomeric structures select sulfur oxygen radical type structure and can be viewed as (RS↓)Fe↑(IV)(O↑)(Por). In horseraddish peroxidase (HRP) and peroxidase with histidine axial ligand π cation radical character of porphyrin ring is preferred (Im)Fe↑(IV)(O↑)(Por↓). For the ligands such as OMe−, OPh− and Cl− oxidation mainly took place on the iron and the active intermediate can be viewed as (L)Fe↑(V)(O)(Por) with one unpaired electron localized on the iron. 相似文献
996.
The crystallization process of a simple liquid upon slow cooling has been modeled by the Monte-Carlo method. The model contains 10,000 Lennard-Jones atoms in the model box with periodic boundary conditions. The model structure is investigated at different stages of crystallization using Delaunay simplices. The simplex belonging to one or another particular crystal structure was determined by the shape of the given simplex taking into account the shape of its neighboring simplices. Simplices typical of the fcc and hcp crystal structures, as well as of polytetrahedral aggregates, not typical of crystals, were studied. The analysis has shown that the “precursors” of a hcp structure are strongly dominating over the “precursors” of a fcc structure in liquid phase before the beginning of crystallization. When crystallization starts, small embryos of the fcc structure are observed; the simplices peculiar to hcp are present at that in great amount, but they are distributed over the sample more uniformly. As crystallization proceeds, the portion of the fcc phase grows faster than hcp. However, no unified crystal appears in our case of slow cooling of the model. A complex polycrystalline structure containing crystalline regions with multiple twinning, pentagonal prisms and elements of icosahedral structures arises instead. 相似文献
997.
N. S. Mosyagin A. V. Titov R. J. Buenker H.‐P. Liebermann A. B. Alekseyev 《International journal of quantum chemistry》2002,88(5):681-686
Multireference single‐ and double‐excitation configuration interaction (MRD‐CI) calculations of transition energies for the Hg atom and spectroscopic constants for the HgH molecule are carried out with the generalized relativistic effective core potential (GRECP) method. A new selection criterium for the reference configurations is discussed. The calculated spectroscopic constants are compared with experimental data and results of calculations of other groups. Improvement of accuracy is mainly observed for bond lengths from the GRECP/MRD‐CI calculations (without applying the T = 0 correction) with respect to the results of other groups. Analysis of the quality of the approximations employed is carried out. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002 相似文献
998.
999.
1000.
Theoretical and Experimental Study on the Adsorption and Desorption of Methane by Granular Activated Carbon at 25 ℃ 总被引:1,自引:0,他引:1
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E. Salehi V. Taghikhani C. Ghotbi E. Nemati Lay A. Shojaei 《天然气化学杂志》2007,16(4):415-422
A theoretical and experimental study was conducted to accurately determine the amount of adsorption and desorption of methane by various Granular Activated Carbon(GAC)under different physical conditions.To carry out the experiments,the volumetric method was used up to 500 psia at constant temperature of 25℃.In these experiments,adsorption as well as desorption capacities of four different GAC in the adsorption of methane,the major constituent of natural gas,at various equilibrium pressures and a constant temperature were studied.Also,various adsorption isotherm models were used to model the experimental data collected from the experiments.The accuracy of the results obtained from the adsorption isotherm models was compared and the values for the regressed parameters were reported.The results shows that the physical characteristics of activated carbons such as BET surface area,micropore volume,packing density,and pore size distribution play an important role in the amount of methane to be adsorbed and desorbed. 相似文献