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We report the reductive elimination of haloarene from {Pd[P(o-tol)3](Ar)(μ-X)}2 (X = Cl, Br, I) upon addition of the strongly electron-donating, but sterically hindered, phosphine P(t-Bu)3 and related ligands. Reductive elimination of aryl chlorides, bromides, and iodides from these dimeric arylpalladium(II) halide complexes was observed upon the addition of P(t-Bu)3. Conditions to observe the elimination and addition equilibria were established for all three halides, and values for these equilibrium constants were measured. Reductive elimination of aryl chlorides was most favored thermodynamically, and elimination of aryl iodide was the least favored. However, reactions of the aryl chloride complexes were the slowest. Detailed mechanistic data revealed that cleavage of the starting dimer, accompanied by ligand substitution either before or after cleavage, led to the formation of a three-coordinate arylpalladium(II) halide monomer that reductively eliminated haloarene.
The synthesis of unsymmetrically or non-uniformly surface-functionalized dendritic macromolecules using a stepwise convergent-growth approach is described. By stepwise alkylation of the monomer unit, 3,5-dihydroxybenzyl alcohol, with unsubstituted and substituted benzylic bromides, followed by activation of the group located at the focal point, dendritic 'wedges' can be obtained in which there is only a single substituent such as a cyano group at the periphery. Use of only substituted benzylic bromides in the first step of growth allows fully functionalized dendritic wedges to be obtained. Coupling to a polyfunctional core such as 1,1,1-tris-(4′-hydroxyphenyl)ethane can also be done in a stepwise manner with both mono or fully substituted and unsubstituted 'wedges' to give dendritic macromolecules containing one, two, or three cyano groups or sixteen or thirty-two bromine atoms at the periphery of the macromolecule. These hyperbranched dendritic polymers were purified by normal flash chromatography and fully characterized by a combination of spectroscopic and chromatographic techniques. By using variations of this general scheme both the number and placement of the functional groups at the periphery of the dendritic macromolecule can be accurately controlled to afford a large variety of functionalized hyperbranched moieties.
A study has been made of the role of aging treatment in influencing fatigue crack propagation and crack closure behavior in a high purity ingot metallurgy aluminum alloy 7150, with specific reference to crack growth at low and high load ratios in the near-threshold regime. A trend of increasing growth rates and decreasing threshold stress intensity ΔK th values with increased aging was seen to be consistent with lower measured levels of crack closure and a decreasing tortuosity in crack path. On the basis of crack growth measurements in moist room air, where closure due to corrosion product formation was found to be negligible in this alloy, the superior fatigue resistance of underaged microstructured (compared with overaged structures of similar strength and peak-aged structures of higher strength) was attributed to greater slip reversibility and to enhanced roughness-induced crack closure and deflection from the more tortuous crack paths. Such factors are promoted in alloy systems hardened by coherent shearable precipitates where the mode of deformation is one of non-homogeneous planar slip.
Abstract A procedure is presented to analyse the response of concrete gravity dams due to horizontal and vertical earthquake ground motion components considering dam‐water interaction and partial absorption of hydrodynamic pressure waves at the reservoir bottom into the foundation medium. The effects of reservoir bottom absorption on the hydrodynamic force on a rigid dam are examined first. The harmonic response of an idealized dam cross‐section is presented for a wide range of parameters characterizing the properties of the dam, the impounded water and the foundation medium. Based on these frequency response functions the effects of dam‐water interaction and of reservoir bottom absorption in the response of dams due to horizontal and vertical components of ground motion are investigated.
We have performed Monte Carlo simulations of type Ia supernova (SN Ia) surveys to quantify their efficiency in discovering peculiar overluminous and underluminous SNe Ia. We determined how the type of survey (magnitude-limited, distance-limited, or a hybrid) and its characteristics (observations frequency and detection limit) affect the discovery of peculiar SNe Ia. We find that there are strong biases against the discovery of peculiar SNe Ia introduced by at least four observational effects: the Malmquist bias, the age of the SN Ia at the time of its discovery, the shape of its light curve, and its degree of extinction. Surveys with low observation frequency (less than once per 10 days) tend to discover SNe Ia which are too old for observers to easily recognize their peculi arity. Subluminous SNe Ia are underrepresented in magnitude-limited surveys because they can only be found within a small volume and they remain above the detection limit for less time. Conversely, overluminous SNe Ia are more easily found in magnitude-limited surveys although their likely association with dusty regions reduces the volume in which they can be discovered. The unbiased rate of peculiar SNe Ia can be recovered only in distance-limited surveys with high observation frequencies and with detection limits which are fainter than the peak magnitude of a subluminous SN Ia in the farthest potential host.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTUse of intermolecular hydrogen bonding for the induction of liquid crystallinity in the side chain of polysiloxanes. [Erratum to document cited in CA117(10):90961a]Uday Kumar, Takashi Kato, and Jean M. J. FrechetCite this: J. Am. Chem. Soc. 1992, 114, 25, 10093Publication Date (Print):December 1, 1992Publication History Published online1 May 2002Published inissue 1 December 1992https://pubs.acs.org/doi/10.1021/ja00051a072https://doi.org/10.1021/ja00051a072research-articleACS PublicationsRequest reuse permissionsArticle Views87Altmetric-Citations3LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
A two-dimensional (2-D) cellular neural network (CNN) array of resistively coupled Chua circuits which can be designed to implement some elementary aspects of spatial recognition, namely, distinguishing open curves from closed ones and locating the shortest path between two locations, is described. In the latter, two situations are analyzed: flat and wrinkled surfaces. The 2-D CNN array of Chua circuits is shown to be capable of finding the shortest path between two points on a wrinkled labyrinth. The performance of this parallel processing approach was examined using computer simulations, although this method can be implemented in real time via VLSI technology.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
In recent times, Bangladesh has experienced increased environmental degradation in general, particularly industrial pollution. The effect of industrial pollution is huge and the country is affected badly in a socio-economic way. This article emphasizes the problem of industrial pollution with regard to the present status of the environment in Bangladesh. It contains a summary of the country’s major environmental problems, a compilation of varied information on industrial pollution, and its effects. In the end, this article gives a silver lining on the magnitude of the problem and strategies for handling industrial waste management in an environment-friendly way.
Continuous piecewise-linear functions from R/sup n/ to R/sup m/ are characterized by the geometry of their region boundaries. The notions of the nonlinearity component and of the order of boundary intersections are introduced. The theory developed makes it possible to determine the exact number of independent parameters for a given class of setups.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
