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排序方式: 共有94条查询结果,搜索用时 46 毫秒
1.
New hafnocene triarylstannyl complexes were prepared and were shown to undergo clean thermal decompositions via alpha-aryl-elimination to produce the corresponding stannylene and a hafnocene aryl complex. The rate of the decomposition is highly dependent on the nature of the ancillary ligand, with the stabilities of the CpCp*Hf(SnPh(3))X compounds following the order X = NMe(2) > Np (alpha-agostic) > OMe > Cl > Me. Mechanistic information suggests that alpha-aryl-elimination may be viewed as a concerted process involving nucleophilic attack of the migrating aryl group onto the electrophilic metal center. 相似文献
2.
The effects of a ready-made surfactant (sodium dodecyl sulfate) on the dynamic interfacial tension between a model acidic oil (linoleic acid dissolved in paraffin oil) and various aqueous alkaline (NaOH) systems have been studied using pendant drop tensiometry at surfactant concentrations both below and above the critical micelle concentration (CMC). Below the CMC the added surfactant contributes significantly to a further reduction of interfacial tension of the reacting acid/alkaline system, whereas above the CMC the added surfactant plays an important role in damping the dynamic trends observed for the reactive system alone. Copyright 2001 Academic Press. 相似文献
3.
Multiconfiguration calculations have been performed in order to estimate ab initio energies for the configuration 3p4p in Si I. A preliminary attempt has also been made to calculate E2 transition rates for transitions from levels of 3p 2 to those of 3p4p. However, these rates show a gauge dependence, which indicates that further correlation needs to be included to obtain accurate rates and lifetimes. 相似文献
4.
Thomas O. Richardson Nancy Neale Natosha Carwell 《Journal of heterocyclic chemistry》1995,32(1):359-361
The synthesis of the quinolone, 7-ethyl-3-methyl-4,7-dihydro-4-oxoisothiazolo[5,4-b]pyridine-5-carboxylic acid 4 was accomplished utilizing the Gould-Jacobs dependent route. The compound had very weak in vitro activity as compared to nalidixic acid versus E. coli, P. aeruginosa, K. pnuemoniae, S. aureus and P. mirabilis. 相似文献
5.
Electrochemical investigations of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) have been conducted in a Ca2+-containing dimethyl sulfoxide electrolyte. While the ORR appears irreversible, the introduction of a tetrabutylammonium perchlorate (TBAClO4) co-salt in excess concentrations results in the gradual appearance of a quasi-reversible OER process. Combining the results of systematic cyclic voltammetry investigations, the degree of reversibility depends on the ion pair competition between Ca2+ and TBA+ cations to interact with generated superoxide (O2−). When TBA+ is in larger concentrations, and large reductive overpotentials are applied, a quasi-reversible OER peak emerges with repeated cycling (characteristic of formulations without Ca2+ cations). In situ Raman microscopy and rotating ring-disc electrode (RRDE) experiments revealed more about the nature of species formed at the electrode surface and indicated the progressive evolution of a charge storage mechanism based upon trapped interfacial redox. The first electrochemical step involves generation of O2−, followed primarily by partial passivation of the surface by CaxOy product formation (the dominant initial reaction). Once this product matrix develops, the subsequent formation of TBA+--O2− is contained within the CaxOy product interlayer at the electrode surface and, consequently, undergoes a facile oxidation reaction to regenerate O2.An interlayer product of oxygen reduction with Ca2+/TBA+ yields a quasi-reversible oxygen evolution reaction by inducing a trapped interfacial redox process. 相似文献
6.
7.
Krystel K. Castillo-Villar Neale R. Smith James L. Simonton 《Applied Mathematical Modelling》2012,36(12):5920-5935
Recent studies have shown that the cost of quality (COQ) is of more strategic and economic importance than previously conceived. Whereas previous works have applied COQ as an internal performance measure within companies, the purpose of this paper is to present a model for supply chain design that computes the COQ as a global performance measure for the entire supply chain. In addition, rather than assume an exogenously given COQ curve, our model computes COQ in terms of internal operational decisions such as the error rate at inspection and fraction defective at manufacturing. The model can be used to design a logistic route that achieves a minimum total cost while maintaining an overall quality level and to evaluate the impact of investment in quality to increase overall profits. The behaviour of the model is illustrated with numerical examples that show how the COQ function changes depending on various parameters. 相似文献
8.
9.
Matthew J. Evans Mathew D. Anker Claire L. McMullin Samuel E. Neale Nasir A. Rajabi Martyn P. Coles 《Chemical science》2022,13(16):4635
Multiply-bonded main group metal compounds are of interest as a new class of reactive species able to activate and functionalize a wide range of substrates. The aluminium sulfido compound K[Al(NONDipp)(S)] (NONDipp = [O(SiMe2NDipp)2]2−, Dipp = 2,6-iPr2C6H3), completing the series of [Al(NONDipp)(E)]− anions containing Al–E{16} multiple bonds (E{16} = O, S, Se, Te), was accessed via desulfurisation of K[Al(NONDipp)(S4)] using triphenylphosphane. The crystal structure showed a tetrameric aggregate joined by multiple K⋯S and K⋯π(arene) interactions that were disrupted by the addition of 2.2.2-cryptand to form the separated ion pair, [K(2.2.2-crypt)][Al(NONDipp)(S)]. Analysis of the anion using density functional theory (DFT) confirmed multiple-bond character in the Al–S group. The reaction of the sulfido and selenido anions K[Al(NONDipp)(E)] (E = S, Se) with CO2 afforded K[Al(NONDipp)(κ2E,O-EC{O}O)] containing the thio- and seleno-carbonate groups respectively, consistent with a [2 + 2]-cycloaddition reaction and C–E bond formation. An analogous cycloaddition reaction took place with benzophenone affording compounds containing the diphenylsulfido- and diphenylselenido-methanolate ligands, [κ2E,O-EC{O}Ph2]2−. In contrast, when K[Al(NONDipp)(E)] (E = S, Se) was reacted with benzaldehyde, two equivalents of substrate were incorporated into the product accompanied by formation of a second C–E bond and complete cleavage of the Al–E{16} bonds. The products contained the hitherto unknown κ2O,O-thio- and κ2O,O-seleno-bis(phenylmethanolate) ligands, which were exclusively isolated as the cis-stereoisomers. The mechanisms of these cycloaddition reactions were investigated using DFT methods.Reaction of Al–E (E = S, Se) multiple bonds with C O functionalities generates new C–E bonds. 相似文献
10.
A modified model for simulating latent hardening during the plastic deformation of rate-dependent FCC polycrystals 总被引:1,自引:0,他引:1
A strain hardening model for the plastic deformation of rate-dependent FCC crystals is proposed based on experimental observations previously reported for single crystals. This model, which is an extension of that employed by
et al. [1983], includes both the self-hardening and latent hardening of the slip systems. The differential hardening of the latent systems is assumed to arise from the interaction between glide dislocations and forests. With this hardening model and a rate-sensitive crystal plasticity theory, the deformation behavior of FCC polycrystals can be predicted from the deformation response of the constituent single crystals. As examples, the uniaxial tensile behaviour of pure aluminum and copper polycrystals is simulated using the extended model, and the results are compared with published experimental data. The effects of latent hardening on polycrystal deformation, especially on flow stress and the formation of tensile textures, are discussed. 相似文献