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1.
Jeroen J. L. M. Cornelissen W. Sander Graswinckel Alan E. Rowan Nico A. J. M. Sommerdijk Roeland J. M. Nolte 《Journal of polymer science. Part A, Polymer chemistry》2003,41(11):1725-1736
The conformational properties of polymers derived from isocyanodipeptides have been investigated with a combination of model calculations, X‐ray diffraction, and circular dichroism spectroscopy. Depending on the configuration of the side chains, defined arrays of hydrogen bonds along the polymeric backbone are formed. This leads to a well‐defined conformation as, for example, expressed in the formation of lyotropic liquid‐crystalline phases and increased helical stability. Upon the disruption of the hydrogen bonds by a strong acid, a less well‐defined macromolecular conformation is observed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1725–1736, 2003 相似文献
2.
José L. Ló pez Nico M. Temme 《Transactions of the American Mathematical Society》2004,356(11):4323-4342
Taylor expansions of analytic functions are considered with respect to several points, allowing confluence of any of them. Cauchy-type formulas are given for coefficients and remainders in the expansions, and the regions of convergence are indicated. It is explained how these expansions can be used in deriving uniform asymptotic expansions of integrals. The method is also used for obtaining Laurent expansions in several points as well as Taylor-Laurent expansions.
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István E. MarkóJean-Christophe Vanherck Ali AtesBernard Tinant Jean-Paul Declercq 《Tetrahedron letters》2003,44(16):3333-3336
Upon treatment with tBuOK/H2O, a variety of ω-halo-β-keto-ketals undergo smooth cyclisation, affording in excellent yields mono-protected [n,m] spiro bicyclic diketones. This transformation is highly stereoselective producing, in all cases, the diastereoisomerically pure spiro derivatives. 相似文献
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The ligand‐exchange mechanism of solvated Be2+ cations has been studied by means of DFT calculations (RB3LYP/6‐311+G**). Ligand exchange around [BeL4]2+, where L=H2O, NH3, CO2, formaldehyde (H2CO), HCN, N2, and CO, was found to follow an associative interchange (Ia) process in all cases. The size of the activation barrier is almost independent of the type of donor atom, and depends mainly on the hybridization undergone by the donor atom. This, in turn, suggests that steric effects play a major role in solvent‐ and ligand‐exchange reactions in Be2+ systems. 相似文献
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J. Nasielski S. Heilporn R. Nasielski-Hinkens
B. Tinant
J. P. Declercq 《Tetrahedron》1989,45(24):7795-7804When quinoxaline-N-oxide 1 is reacted with KCN and benzoyl chloride in water (the Reissert reaction) or methanol, the products are 2-,5- and 6- chloroquinoxaline (the latter being the major product: 42±6 %) and small amounts of 2-cyanoquinoxaline. Using three equivalents of trimethylsilyl cyanide instead of KCN, and dichloromethane as the solvent, leads to a 72 % yield of 2-cyanoquinoxaline. The reaction of trimethylsilyl cyanide and benzoyl chloride with 2,3-diphenylquinoxaline-N-oxide 2 leads to an unexpected ring-opening product 13; its structure is based on spectroscopic data and on an X-ray crystallographic analysis. 相似文献
10.
Moni Chauhan Claude Chuit Robert J. P. Corriu Catherine Rey Jean-Paul Declercq Antoine Dubourg 《Journal of organometallic chemistry》1996,510(1-2):173-179
The X-ray structure analysis of bis(8-dimethylamino-l-naphthyl)phenylphosphane (3) and of the corresponding sulphide 4 has revealed hexacoordination at phosphorus in both cases, the N … P separations being less than the sum of the van der Waal radii. Furthermore, in both cases the overall geometry corresponds to a distorted bicapped tetrahedron. The optimum geometry calculated for 4 via the
program developed by Autodesk (MM + method) suggests that the structure of the molecule is a function not only of steric requirements but also of electronic effects. 相似文献