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61.
Iodine and the pincer complex [Pd(O,N,C-L)I], where L is the monoanionic ligand resulting from deprotonation of the acetyl group of the dimethylmonoketal of 2,6-diacetylpyridine, are in equilibrium at low temperatures with the palladium(IV) complex [Pd(O,N,C-L)I(3)], which can be isolated at -40 °C and characterized by (1)H NMR spectroscopy and X-ray diffraction studies, in spite of its great instability. When the same reaction is carried out at room temperature, a quantitative reductive elimination process occurs, giving L-I, which in the presence of water affords L'-I, resulting from hydrolysis of L-I. 相似文献
62.
Mateo Alajarín Prof. Carmen López‐Leonardo Dr. Ángel Álvarez‐García Pilar Llamas‐Lorente Dr. Pilar Sánchez‐Andrada Dr. José Berná Dr. Aurelia Pastor Dr. Delia Bautista Dr. Peter G. Jones Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(12):3728-3735
A series of N,P,P‐trisubstituted aminophosphanes react with diphenylcyclopropenone to afford an easily separable mixture of two diastereomeric α,β‐diphenyl‐β‐phosphinoyl carboxamides in good yields. X‐ray crystal structures reveal that these compounds associate into dimers, formed from two enantiomeric units linked by two bifurcated hydrogen bonds, whereby the oxygen atom of the phosphoryl group acts as a dual acceptor for the vicinal NH and CH of a carbonyl group of a neighbouring molecule. Studies on the interconversion between diastereomeric phosphinoyl carboxamides in basic solution show that the thermodynamically most stable isomer depends on the nature of the substituent at the nitrogen atom. Simple computational calculations explain this phenomenon. 相似文献
63.
The present review presents the state of the art of the developments, key strategies and analytical applications of chemiluminescence detection coupled to CE (CE‐CL). Different parts considering the most common CL systems have been included, such as the tris(2,2′‐bipyridine)ruthenium(II) system, the luminol and derivatives reaction, the peroxyoxalate CL or direct oxidations. New advances in homemade configurations and applications in different fields such as clinical, pharmaceutical, environmental and food analysis have been included. The focus is on studies which appeared from 2000 to the end of 2009. 相似文献
64.
Alajarín M Pastor A Orenes RA Martínez-Viviente E Pregosin PS 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(3):877-886
Compounds formed by linking two tris(ureidobenzyl)amine modules with a hexamethylene tether are described. These compounds self-assemble to form bicapsular aggregates featuring two rings of six hydrogen-bonded ureas. (1)H and (1)H/(1)H ROESY NMR spectroscopy, together with pulsed gradient spin echo (PGSE) NMR diffusion measurements, have been used to characterize the dimers in solution. The results have been compared with energy-minimized structures. The new compounds are kinetically stable on the NMR timescale, and their thermodynamic stabilities are comparable to other capsular aggregates derived from tris(ureidobenzyl)amines. 相似文献
65.
Cristofor I. Simionescu Geta David Vasile Paraschiv Aurelia Ioanid Sorin Manolache Bogdan C. Simionescu 《Journal of polymer science. Part A, Polymer chemistry》1996,34(15):3071-3076
The kinetic study of the photochemical polymerization of methacrylic acid (MAA) in aqueous dilute solution in the presence of poly(N-acetyliminoethylene) (PNAI) oligomers evidenced template features. The process proceeded in two stages, depending on [PNAI]/[MAA]0 ratio and polymerization duration, two different complexes being formed, both by a “zip” chain-growth mechanism. Computing and transmission electron microscopy data revealed that this aspect is due to the replacing of the initial PNAI template by the newly formed poly(methacrylic acid) daughter polymer, as a result of the structural peculiarities of the latter as a component of the primary complex. Its specific mode of packing in a complex aggregate was considered to be the main reason for the reported behavior. © 1996 John Wiley & Sons, Inc. 相似文献
66.
67.
The movements of free liquid drops, resulting from unbalanced surface tension gradients, in our case the adsorption of a surfactant, constitute important surface phenomena (Marangoni effect). The aim of this paper is to correlate the effect of pressure forces on the drop, with the surface coverage degree, namely with the extent to which the drop surface is covered by the surfactant. Our model shows that for a covered degree less then about 68°, these forces are negative. This means that these forces exerted by the external liquid upon the drop are oriented towards the negative direction of the normal to the drop surface, acting like a hammer. Some numerical data are given. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
68.
Maria Zaharescu Maria Crisan A. Jitianu D. Crisan Aurelia Meghea Ileana Rau 《Journal of Sol-Gel Science and Technology》2000,19(1-3):631-635
Composite SiO2-iron oxide materials were prepared by three experimental procedures. In the first case (1), the iron oxides were precipitated during the sol-gel process. In the second case (2), the SiO2 matrix was initially obtained, and the iron oxides were formed by thermal treatment after impregnation of a soluble Fe2+ salt in the previously processed matrix. In the third method (3), ferrite powders, prepared by wet chemical method, were embedded into a SiO2 based sol-gel matrix. Two type of precursors (tetraethoxysilane (TEOS) or methyltriethoxysilane (MTEOS) were used as SiO2 sources. Various properties versus both type of precursor and on the method of preparation were noticed. Materials with high porosity and nano-sized iron oxide content could be prepared using the mentioned above methods. 相似文献
69.
70.
The dependence of the surface Si/Al ratio in function of the volume Si/Al ratio was studied, for zeolite of type: A, X, clinoptilolite, mordenite and three samples of ZSM-5. Surface measurements were made by Auger electron spectroscopy (AES), and volume (bulk) measurements by atomic absorption spectrophotometry. It was found that the surface Si/Al ratio is identical with the volume Si/Al ratio. The dependence of the surface Si/Al ratio on the crystallization degree for zeolite ZSM-5 was also studied. We obtained some informations about the kinetics and mechanism of the crystallization process. 相似文献