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31.
From a range of preparative methods, three geometric isomers of bis(diphenylarsino)methane‐dichloroplatinum(II) have been isolated, viz. cis‐PtCl2(dpam), trans, trans‐Pt2Cl4(dpam)2 and cis, trans‐Pt2Cl4(dpam)2. Their structures were determined by single‐crystal X‐ray diffraction. 相似文献
32.
用密度泛函理论(DFT)在B3LYP/6-31G(d, p)的计算水平上研究了离子液中1-乙基-3-甲基咪唑阳离子(EMIM+)的4-H和5-H原子催化丁烯双键异构反应的可能途径,优化了反应体系的平衡态和过渡态的几何构型,分析了反应过程中键参数的变化,通过振动分析对平衡态和过渡态进行了验证. 计算结果表明, 离子液中的EMIM+首先通过4-H和5-H原子吸附丁烯, 进而催化丁烯的双键异构反应, EMIM+的4-H和5-H催化1-丁烯异构为2-丁烯的正反应活化能分别为204.2和207.3 kJ•mol-1,逆反应活化能约为220.9和223.8 kJ•mol-1, 反应为基元反应. 相似文献
33.
Jianjun Xu 《Journal of fluorine chemistry》2004,125(5):725-730
High E/Z ratio (E/Z>75:25) 1-bromo-1-fluorostyrenes, which were prepared by isomerization of 1-bromo-1-fluorostyrenes (E/Z≈1:1), underwent the Heck reaction with methyl acrylate, and (2E, 4Z)-methyl 5-aryl-4-fluoropenta-2,4-dienoates were successfully isolated. Heck reactions of (Z)-1-bromo-1-fluorostyrenes also occur. However, the products are difficult to separate in a pure form, since they have an obvious tendency to isomerize on a silica gel column. 相似文献
34.
The 60 even permutations of the ligands in the five-coordinate complexes, ML
5, form the alternating group A
5, which is isomorphic with the icosahedral pure rotation group I. Using this idea, it is shown how a regular icosahedron can be used as a topological representation for isomerizations of the five-coordinate complexes, ML
5, involving only even permutations if the five ligands L correspond either to the five nested octahedra with vertices located at the midpoints of the 30 edges of the icosahedron or to the five regular tetrahedra with vertices located at the midpoints of the 20 faces of the icosahedron. However, the 120 total permutations of the ligands in five-coordinate complexes ML
5 cannot be analogously represented by operations in the full icosahedral point group I
h, since I
his the direct product I×C2 whereas the symmetric group S
5 is only the semi-direct product A
5S2. In connection with previously used topological representations on isomerism in five-coordinate complexes, it is noted that the automorphism groups of the Petersen graph and the Desargues-Levi graph are isomorphic to the symmetric group S
5 and to the direct product S
5×S
2, respectively. Applications to various fields of chemistry are briefly outlined. 相似文献
35.
A series of β,γ‐unsaturated ketones were isomerized to their corresponding α,β‐unsaturated ketones by the introduction of DABCO in iPrOH at room temperature. The endo‐cyclic double bond (β,γ‐position) on ketone was rearranged to exo‐cyclic double bond (α,β‐position) under the reaction conditions. 相似文献
36.
Epimerization of d-glucose and d-mannose, catalyzed by the water soluble complexes of Cu(II), Ni(II), Co(II) and Cd(II) with bisnitrogen ligands 4–7, and by Mo(VI) complexes prepared in situ from ammonium heptamolybdate (AHM) with ligands 4–9 is compared. All examined complexes exhibit lower catalytic activity than AHM: strong coordination of the ligands by both (N,O) heteroatoms to metal ions, presumably affords catalytically less active species. Some free ligands and their metal (II) complexes catalyze both C(2) epimerization and isomerization of aldoses to d-fructose. 相似文献
37.
Miscibility and phase separation in SAN/PMMA blends have been investigated using DSC, IR spectroscopy and positron lifetime spectroscopy (PLS). Single broad glass transition observed throughout the blend compositions, may be due to overlap of two glass transitions. IR measurements clearly indicate the absence of strong interactions. This supports miscibility is due to intramolecular repulsive forces in the SAN component. On the other hand, free volume data show negative deviation from linear additivity indicating the blends are miscible. The interchain interaction parameter β exhibits a complex behavior and the extent of miscibility is not revealed. Following Wolf’s treatment, we have evaluated the geometry factor γ and hydrodynamic interaction parameter α and found α is a suitable parameter in predicting the miscibility window. The cloud points in SAN/PMMA blends increase with decreasing PMMA content. The change in free volume size correlates well with the observed change in cloud point. 相似文献
38.
R. S. Dembo 《Mathematical Programming》1979,17(1):156-175
In this paper we analyse algorithms for the geometric dual of posynomial programming problems, that make explicit use of second order information. Out of two possible approaches to the problem, it is shown that one is almost always superior. Interestingly enough, it is the second, inferior approach that has dominated the geometric programming literature.This work was partially supported by the National Research Council of Canada, Grant A3552 and National Science Foundation Grant ENG78-21615.Earlier versions of this paper were presented at the Optimization Days Conference in Montreal (May 1976) and the TIMS meeting in Athens (July 1977). 相似文献
39.
再论Pedoe不等式的高维推广及应用 总被引:31,自引:0,他引:31
本文对欧氏空间E~n中的两个n维单形,给出了著名的Pedoe不等式的一个实质性推广,并讨论了它的应用. 相似文献
40.
In this paper, we prove the existence and uniqueness of relaxation oscillation cycle of a slow–fast modified Leslie–Gower model via the entry–exit function and geometric singular perturbation theory. Numerical simulations are also carried out to illustrate our theoretical result. 相似文献