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21.
Marconi N. Peas‐Defrutos Camino Bartolom Max García‐Melchor Pablo Espinet 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(11):3539-3543
By combining kinetic experiments, theoretical calculations, and microkinetic modeling, we show that Pf/Rf (C6F5/C6Cl2F3) exchange between [AuPf(AsPh3)] and trans‐[RhRf(CO)(AsPh3)2] does not occur by typical concerted Pf/Rf transmetalation via electron‐deficient double bridges. Instead, it involves asymmetric oxidative insertion of the RhI complex into the (Ph3As)Au?Pf bond to produce a [(Ph3As)Au?RhPfRf(CO)(AsPh3)2] intermediate, followed by isomerization and reductive elimination of [AuRf(AsPh3)]. Interesting differences were found between the LAu?Ar asymmetric oxidative insertion and the classical oxidative addition process of H2 to Vaska complexes. 相似文献
22.
23.
Janine Wolf Camino M. González Tanarro Michael Gütschow Joachim Sieler Bärbel Schulze 《Helvetica chimica acta》2008,91(1):35-45
The synthesis of novel triaryl‐substituted 4‐(isothiazol‐3‐yl)morpholines 7 and 8 , and 1‐(isothiazol‐3‐yl)piperazines 9 – 13 by reaction of the corresponding isothiazolium salts 5 and 6 with secondary amines in the presence of t‐BuOK in absolute THF is described. Some representatives of the isothiazoles were evaluated as inhibitors of acetylcholinesterase from Electrophorus electricus. 相似文献
24.
Bartolomé C Carrasco-Rando M Coco S Cordovilla C Martín-Alvarez JM Espinet P 《Inorganic chemistry》2008,47(5):1616-1624
Isocyanide [AuX(CNPy-2)] (X = Cl, C6F5, fluoromesityl, 1/2 octafluorobiphenyl) and carbene [AuX{C(NR1R2)(NHPy-2)}] (R1R2NH = primary or secondary amines or 1/2 primary diamine) gold(I) complexes have been synthesized and characterized. For X = Cl, the carbene complexes show aurophilic interactions. The fragment NHPy-2, formed in the carbenes, can give rise to intra- (for primary amines) or intermolecular (for secondary amines) hydrogen bonds, depending on the amine used. These bonds and contacts have been studied in the solid state and in solution. The intermolecular hydrogen bonds are split in an acetone solution, but the intramolecular ones, which close a six-membered ring, survive in solution. Except for the fluoromesityl derivatives, the carbene complexes display luminescent properties. 相似文献
25.
Ramiro Varela Camino R. Vela Jorge Puente María Sierra Inés González-Rodríguez 《Annals of Operations Research》2009,166(1):125-146
We confront a practical cutting stock problem from a production plant of plastic rolls. The problem is a variant of the well-known
one dimensional cutting stock, with particular constraints and optimization criteria defined by the experts of the company.
We start by giving a problem formulation in which optimization criteria have been considered in linear hierarchy according
to expert preferences, and then propose a heuristic solution based on a GRASP algorithm. The generation phase of this algorithm
solves a simplified version which is rather similar to the conventional one dimensional cutting stock. To do that, we propose
a Sequential Heuristic Randomized Procedure (SHRP). Then in the repairing phase, the solution of the simplified problem is
transformed into a solution to the real problem. For experimental study we have chosen a set of problem instances of com-mon
use to compare SHRP with another recent approach. Also, we show by means of examples, how our approach works over instances
taken from the real production process.
All authors are supported by MEC-FEDER Grant TIN2007-67466-C02-01 and by contract CN-05-127 of the University of Oviedo and
the company ERVISA, and by FICYT under grant BP04-021. 相似文献
26.
A kernel of a directed graph is a set of vertices which is both independent and absorbent. And a digraph is said to be kernel perfect if and only if any induced subdigraph has a kernel. Given a set of arcs F , a semikernel S modulo F is an independent set such that if some Sz-arc is not in F , then there exists a zS-arc. A sufficient condition on the digraph is given in terms of semikernel modulo F in order to guarantee that a digraph is kernel perfect. To do that we give a characterization of kernel perfectness which is a generalization of a previous result given by Neumann-Lara [Seminúcleos de una digrfica. Anales del Instituto de Matemticas 2, Universidad Nacional Autónoma de México, 1971]. And moreover, we show by means of an example that our result is independent of previous known sufficient conditions. 相似文献
27.
Given a vertex v of a graph G the second order degree of v denoted as d 2(v) is defined as the number of vertices at distance 2 from v.In this paper we address the following question:What are the sufficient conditions for a graph to have a vertex v such that d2(v) ≥ d(v),where d(v) denotes the degree of v? Among other results,every graph of minimum degree exactly 2,except four graphs,is shown to have a vertex of second order degree as large as its own degree.Moreover,every K-4-free graph or every maximal planar graph is shown to have a vertex v such that d2(v) ≥ d(v).Other sufficient conditions on graphs for guaranteeing this property are also proved. 相似文献
28.
It is shown that, by the addition of a typical intumescent mixture of ammonium polyphosphate and pentaerythritol to polypropylene, the mechanism of intumescence which develops on heating is not significantly affected by dispersion of the intumescent mixture in the polymer. On the other hand, in these mixtures, polypropylene seems to evolve, by thermal degradation, a smaller amount of flammable products than when it is heated alone. The ammonium polyphosphate-pentaerythritol additive is shown to induce fire retardant characteristics in polypropylene by means of a ‘condensed phase’ mechanism. 相似文献
29.
The mechanism by which a typical fire retardant chloroparaffin imparts fire retardant characteristics to high density polyethylene, polypropylene and polystyrene is studied by comparing the oxygen indices of these mixtures measured before and after dehydrochlorination. It is shown that flame poisoning by HCl evolved from the chloroparaffin is negligible in polystyrene and high density polyethylene, whereas it is noticeable in polypropylene. The results obtained are related to previous data on the thermal degradation of these mixtures. It is concluded that the chloroparaffin acts mainly by modifying the mechanism of pyrolysis of these polymers in the burning process. Only in the case of polypropylene is there an appreciable contribution by flame poisoning. 相似文献
30.
Menéndez FE Espina Aránzazu Trobajo Camino García José R. Rodríguez Julio 《Journal of inclusion phenomena and macrocyclic chemistry》1993,15(3):215-230
Journal of Inclusion Phenomena and Macrocyclic Chemistry - The intercalation reactions betweenn-alkylamines and α-titanium phosphate in aqueous media have been investigated. The compounds with... 相似文献