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61.
62.
ISSIe山和W6flSChllh山子1960年首次用pdCI。和二苯基磷合成出黄色的二聚络合物,后被H。yieY*确认为具有pRZ的桥式结构.此后一系列该类结构的化合物被合成并引起了广泛的兴趣.磷可以和两个甚至多个金属原子络合构成多核金属络合物,在催化反应中有重要应用.磷原子存在多种电子态,其3d空轨道也能参与成键.P乃1的NMR谱是研究含磷化合物立体结构的有力工具.P-31与其它核素之间的耦合常数以及P-31的化学位移对阐明化合物的立体构象以及电子结构具有重要作用.近年来,West饲用计算机神经网络技术预测P-:if的化学位移,但仅… 相似文献
63.
Tingmin Wang Jerald S. Bradshaw Janet C. Curtis Peter Huszthy Reed M. Izatt 《Journal of inclusion phenomena and macrocyclic chemistry》1993,16(2):113-122
Significant - interaction is found in the complexes of (S, S)-dimethylpyridino-18-crown-6 with (R)- and (S)-[-(1-naphthyl)ethyl]ammonium perchlorate. This finding is supported by the1H NOESY NMR spectral technique, greater chemical shift changes of aromatic protons in both host and guest molecules upon complexation, and by molecular mechanics calculations. Because of the flexibility of the ligand, the tripod hydrogen bonding causes13C relaxation times of all periphery carbons to decrease without significant selectivity. Rotational energy barrier calculations of the methyl groups of the complexed ligand also show that the (S, S)-host-(R)-guest is the more stable complex. 相似文献
64.
DFT calculations have been performed to determine the isomer shift for a series of iron(II) clusters with nitrogen-containing ligands which serve as models of coordination units in Fe(II) complexes with 1,2,4-triazoles possessing a 1 A 1 ? 5 T 2 spin transition. Good agreement has been found between the theoretical and experimental values of the isomer shift for both low-and high-spin phases. Our calculations confirmed the hypothesis about relationship between the experimentally observed differences in the isomer shift for the low-spin phases of the complexes and variations of the Fe-N mean bond length. 相似文献
65.
66.
Sittichai Natesakhawat Xueqin Wang Lingzhi Zhang Umit S. Ozkan 《Journal of molecular catalysis. A, Chemical》2006,260(1-2):82-94
Chromium-free iron-based catalysts were prepared and studied in regard to their performance in the high-temperature water-gas shift reaction (HTS). The effects of various catalyst preparation variables (i.e., Fe/promoter ratio, pH of precipitation medium, calcination and reduction temperatures) and preparation methods were investigated. Aluminum is a potential chromium replacement in HTS catalysts. Further improvement in WGS activity of Fe–Al catalysts can be achieved by the addition of small amounts of copper or cobalt. Catalysts were characterized using BET surface area measurements, temperature-programmed reduction (TPR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). As a textural promoter, aluminum and chromium prevent the sintering of iron oxides and stabilize magnetite phase by retarding its further reduction to FeO and metallic Fe. The promotional effect of Cu is found to be strongly dependent on the preparation method. 相似文献
67.
Summary The solution conformations of 1,4-diaryl-tetrahydro-1H,3H-furo[3,4-c]furans were determined by means of the LIS technique using a modified LIS-simulation program specially designed for the requirements of the aromatic 1,2,3-trimethoxy arrangement as a bidentate coordination site for the NMR shift reagent. The resulting geometries were confirmed by force field calculations (MM2-87) and compared with X-ray derived structures. Reliable data for the conformations in solution allowed a quantitative estimation of the circular dichroism based on the coupled oscillator model.
Lanthanideninduzierte Verschiebungen von aromatischen 1,2,3-Trimethoxy-Verbindungen: Konformationsanalyse von Tetrahydrofurofuran-Lignanen in Lösung
Zusammenfassung Es wurden mittels der LIS-Technik die Konformationen von 1,4-Diaryl-tetrahydro-1H,3H-furo[3,4-c]furanen in Lösung bestimmt. Dazu mußte ein modifiziertes LIS-Simulationsprogramm entworfen werden, das auf die besonderen Verhältnisse der aromatischen 1,2,3-Trimethoxy-Gruppierung eingeht, welche in den untersuchten Verbindungen als zweizähnige Koordinationsstelle für das NMR-Verschiebungsreagens fungiert. Die resultierenden Geometrien wurden mittels Kraftfeldrechnungen (MM2-87) überprüft und soweit vorhanden auch mit Röntgenstrukturdaten verglichen. Für die Lösungskonformationen wurde eine quantitative Abschätzung des Circulardichroismus auf der Basis des Modells für gekoppelte Oszillatoren durchgeführt.相似文献
68.
McDowell SA 《Journal of computational chemistry》2003,24(10):1201-1207
A theoretical study of the properties of the linear LiH dimer was undertaken. In this dimer, an unusual type of hydrogen bonding (termed "inverse" hydrogen bonding by some authors), which involves the hydrogen bonded molecule acting as an electron donor (rather than as a proton donor), is exhibited. The optimized geometry, dipole moment, interaction energy, atomic charges, harmonic vibrational frequencies, and frequency shifts for the dimer are computed at the SCF, MP2, and QCISD levels of theory using mainly a 6-31++G(d,p) basis set. We also examined the relative stability of the mono-deuterated isotopomers of linear (LiH)(2), i.e., Li-H...Li-D and Li-D...Li-H. Analysis of the normal vibrational modes, changes in the partial atomic charges, and changes in the vibrational frequencies of LiH on complexation were used to gain insight into the bonding and properties of the linear LiH dimer and its isotopomers. 相似文献
69.
Gelebe AC Kaye PT Klein R Sewry JD Soper AG 《Magnetic resonance in chemistry : MRC》2005,43(11):952-955
The influence of substituents and structure on the 13C NMR spectra of four series of benzoxathiepine derivatives has been investigated. Signal assignments in the 13C NMR spectra have been facilitated by the use of several predictive methods, permitting comparison of their relative efficacy. 相似文献
70.
Walter Weissensteiner 《Monatshefte für Chemie / Chemical Monthly》1992,123(8-9):785-800
Summary The conformational possibilities of 5-(3-N,N-dimethylaminopropyl)-5H-dibenzo[a,d]cycloheptene (1), 5-(3-N,N-dimethylaminopropylidene)-10,11-dihydro-5H-dibenzo[a,d]cycloheptene (2), and 5-(3-N,N-dimethylaminopropyl)-10,11-dihydro-5H-dibenzo[a,d]cycloheptene (3) are analysed using empirical force field methods. Minimum energy conformations, interconversion pathways, interconversion graphs and interconversion energies are examined in view of the analysis of conformer equilibria of1,2, or3 in solution. In addition, some basic requirements of the analysis of fast interconverting conformers using the lanthanide induced shift method are discussed.
Konformation und interne Beweglichkeit von 5H-Dibenzo[a,d]cyclohepten Derivaten in Lösung. Konformationsanalyse hochflexibler Strukturen, Teil 2
Zusammenfassung Die konformativen Möglichkeiten von 5-(3-N,N-dimethylaminopropyl)-5H-dibenzo[a,d]cyclohepten (1), 5-(3-N,N-dimethylaminopropylidene)-10,11-dihydro-5H-dibenzo[a,d]cyclohepten (2) und 5-(3-N,N-dimethylaminopropyl)-10,11-dihydro-5H-dibenzo[a,d]cyclohepten (3) wurden mit Hilfe empirischer Kraftfeldmethoden analysiert. Jene Konformationen, die einem energetischen Minimum entsprechen, sowie Interkonversionswege, Interkonversionsgraphen und Interkonversionsenergien wurden in Hinblick auf die Analyse der Konformerengleichgewichte von1,2 oder3 in Lösung untersucht. Weiters werden noch einige grundlegende Voraussetzungen für die Analyse von sich schnell ineinander umwandelnden Konformeren mittels der Lanthaniden-induzierten Verschiebungsmethode besprochen.相似文献