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91.
Pd-catalyzed asymmetric allylic alkylation provides both enantio- and diastereoselectivity in formation of bicyclo [2.2.2] octan-2,3-diones and quinuclidin-2-ones, the latter potential precursors to quinine alkaloids. [reaction: see text] 相似文献
92.
Enrico Abignente Paolo de Caprariis Rosaria Patscot Antonella Sacchi 《Journal of heterocyclic chemistry》1986,23(4):1031-1034
A series of heterocyclic compounds having an imidazole ring fused with another ring with a bridgehead nitrogen atom and bearing a trifluoromethyl moiety was synthesized by reaction of 3-bromo-1,1,1-trifluoroacetone with various heteroarylamines. In some cases, an intermediate compound obtained together with the required product was isolated and its structure was elucidated: e.g., starting from 2-aminopyridine we have obtained 2-trifluoromethylimidazo[1,2-a]pyridine and 2-hydroxy-2-trifluoromethyl-2,3-dihydro-1H-imidazo [1,2-a]pyridinium bromide. Such results confirmed the mechanism previously proposed for this reaction. 相似文献
93.
We address the problem of removing correlation from sets of states while preserving as much local quantum information as possible. We prove that states obtained from universal cloning can only be decorrelated at the expense of complete erasure of local information (i.e., information about the copied state). We solve analytically the problem of decorrelation for two qubits and two qumodes (harmonic oscillators in Gaussian states), and provide sets of decorrelable states and the minimum amount of noise to be added for decorrelation. 相似文献
94.
Cavity ring-down spectroscopy of jet-cooled silane isotopologues in the Si-H stretch overtone region
Absorption spectra of silane in the region of the first overtone of the Si-H stretch vibration have been recorded in a seeded supersonic jet expansion by cavity ring-down spectroscopy as well as in a static gas cell at room temperature by photoacoustic spectroscopy. Spectral simplification due to strong rotational cooling in the jet expansion enables us to clearly resolve and assign the rovibrational transitions of the (2000) and (1100) bands of the three isotopologues, (28)SiH(4), (29)SiH(4), and (30)SiH(4), in their natural isotopic abundance. Interconversion between different nuclear spin species of SiH(4) is found to be absent during the jet expansion. Isotope shifts for (29)SiH(4) and (30)SiH(4) relative to (28)SiH(4) are measured and found to be suitable for selective vibrational excitation of any of three silane isotopologues by pulsed laser excitation in a jet expansion. 相似文献
95.
Caio César Ferreira Florindo Christina Papenfuss Adalberto Bono Maurizio Sacchi Bassi 《Journal of mathematical chemistry》2017,55(10):1985-2003
The aim of the present paper is a continuum theoretical framework for mixtures of different chemical components, including the possibility of chemical reactions. The molecules are assumed to have an orientational degree of freedom, i.e. they are needle-shaped or planar. In the first case the microscopic director is the orientation of the particle long axis, in the second case it is the unit vector normal to the disc. This orientation is introduced as an additional variable in the domain of the field quantities. On this enlarged domain, the mesoscopic space, balance equations are derived. Compared to usual continuum theory, additional fluxes in orientation space occur. These are constitutive functions, like internal energy, heat flux and stress tensor. The restrictions on constitutive functions imposed by the second law of thermodynamics are derived by the method of Liu. Therefore, this new approach is very promising, since microscopic features of the particles, discarded in traditional continuous thermodynamics, become now an important part in the understanding of chemical systems. In addition, the results presented here can be extended to the study of other complex materials such as alloys, ferrofluids, carbon fibers, etc. 相似文献
96.
Giannantonio Sacchi 《Meccanica》1971,6(3):168-171
Summary The expected value of the minimum weight of material necessary for a structure in order to support assigned loads is considered, when the « resistance » of each element is a random quantity.By going back to a theorem which gives a lower bound for this expected value, a way to compute an upper bound is shown.A way of evaluating the variation of the interval of the existence of the average is then set out.Such bounds are functions of random variables but are evaluated on the basis of a deterministic limit design.
Study supported by the C.N.R. (Consiglio Nazionale delle Ricerche). 相似文献
Sommario Richiamato un teorema[4] che fornisce un minorante del valore medio del volume minimo di strutture soggette a carichi noti e dotate di elementi costituiti da materiale a resistenza aleatoria, si dimostra l'esistenza di un maggiorante.Si dimostra poi come sia possibile stabilire un maggiorante ed un minorante della varianza del minimo volume, e quindi come si possa apprezzare il rischio d'errore connesso alla aleatorietà delle resistenze, nella valutazione del volume minimo.I limiti indicati, benchè derivati da elaborazioni statistiche sulle resistenze, risultano da un progetto ottimale sviluppato con soli calcoli deterministici.
Study supported by the C.N.R. (Consiglio Nazionale delle Ricerche). 相似文献
97.
98.
Maria Carmela Sacchi Clelia Cogliati Simona Losio Giovanna Costa Paola Stagnaro Stefano Menichetti Caterina Viglianisi 《Macromolecular Symposia》2007,260(1):21-26
Four comonomers bearing a highly efficient phenolic antioxidant unit and different distance between the antioxidant moiety and the double bond have been prepared and tested in co-polymerization with ethylene by means of three selected metallocene based catalysts. The possibility to obtain a masterbach suitable for melt blending with commercial polyolefins has been evaluated by modifying: i) the structure of the functionalized comonomer, ii) the kind of catalyst, iii) the polymerization conditions. The pair rac-[Me2Si-(2-Me-4,5-BenzInd)2]ZrCl2 catalyst and comonomer with the longest spacer (8 methylene units) allowed the highest comonomer incorporation, while with rac-(EBTHI)ZrCl2 catalyst the highest polymerization activity was observed. TGA analysis has been carried out on some of the copolymers in order to investigate the influence of type and amount of the comonomer on their thermal stability and to test the efficiency of the antioxidant group both in nitrogen and oxygen atmosphere. 相似文献
99.
Random propene/4‐methyl‐1‐pentene copolymers synthesized with C2 symmetric highly isospecific metallocenes
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Maria Carmela Sacchi Simona Losio Luigi Fantauzzi Paola Stagnaro Roberto Utzeri Maurizio Galimberti 《Journal of polymer science. Part A, Polymer chemistry》2015,53(22):2575-2585
Propene (P)/4‐methyl‐1‐pentene (Y) copolymers in a wide range of composition were prepared with isospecific single center catalysts, rac‐Et(IndH4)2ZrCl2 ( EBTHI ), rac‐Me2Si(2‐Me‐BenzInd)2ZrCl2 ( MBI ), and rac‐CH2(3‐tBuInd)2ZrCl2 ( TBI ). 13C NMR analysis of copolymers and statistical elaboration of microstructural data at triad level were performed. Unprecedented and surprising results are here reported. Random P/Y copolymers were prepared with the most isospecific catalyst, TBI , that is known to prepare ethene/propene and ethene/4‐methyl‐1‐pentene copolymers with long homosequences of both comonomers, whereas longer homosequences of both comonomers were observed in copolymers from the less enantioselective metallocenes EBTHI and MBI . These findings, which are against what is acknowledged in the field, can pave the way for the preparation on a large scale of random propene‐based copolymers. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2575–2585 相似文献
100.
Incoronata Tritto Laura Boggioni Maria Carmela Sacchi Paolo Locatelli Dino R. Ferro Augusto Provasoli 《Macromolecular rapid communications》1999,20(5):279-283
A series of ethylene‐norbornene copolymers were synthesized in the presence of zirconocenes with different symmetries and ligand patterns and at different norbornene (N)/ethylene (E) mole ratios. Copolymers were characterized by 13C NMR spectroscopy; Inadequate NMR sequences were used also. The comparison of 13C NMR spectra of copolymers prepared with different norbornene content and the correlation between 13C NMR chemical shifts and conformational structures of the chain on the basis of molecular mechanics calculations were performed. Preliminary assignments were revised and new comonomer sequences such as ENNE which contain meso and racemo NN dyads were assigned. 相似文献