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971.
Emmanuel Lacte Philippe Renaud 《Angewandte Chemie (International ed. in English)》1998,37(16):2259-2262
New prospects for synthetic applications are offered by the 1,2-acyloxy shift of β-(acyloxy)alkyl radicals, which proceeds with high yields under Lewis acidic conditions [Eq. (1)]. With the exception of cyclizations, this is the first Lewis acid mediated acceleration of a radical rearrangement. 相似文献
972.
Philippe Renaud Michle Gerster 《Angewandte Chemie (International ed. in English)》1998,37(19):2562-2579
The neglect of free radicals over the past few years has been overcome, and they are no longer only considered as interesting reactive intermediates with limited synthetic potential. New opportunities are opened up by performing radical reactions in the presence of Lewis acids. Rate enhancement of radical addition to olefins as well as stereochemical control of such reactions can be achieved in a unique manner. Recent examples of enantioselective radical reactions and perspectives for applications in catalysis are discussed. 相似文献
973.
Infrared spectra simulations require ab initio techniques to get reliable intensities. On the other hand, recent force fields can provide accurate molecular geometries and frequencies. Therefore, it is suggested that these new force fields could be used to simulate infrared spectra, dipole-moment surfaces being described at high levels of theory in order to get satisfactory intensities. As pointed out, for a system with N atoms, the cost of such a simulation would be reduced N-fold with respect to standard quantum approaches. Preliminary calculations based on this scheme are reported here. Encouraging results are obtained since no significant lost of accuracy is noted on going from the ab initio to the molecular mechanics potential energy surface. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 69: 705–711, 1998 相似文献
974.
975.
Laurence Lecamp Philippe Lebaudy Boulos Youssef Claude Bunel 《Macromolecular Symposia》1999,148(1):77-86
Photoinitiated polymerization of multifunctional monomers is an usual method to prepare highly crosslinked networks which have a wide variety of applications. This method leads to high reaction rates and the resulting exothermic effect of this reaction can be the cause of defects in the final material. The heterogeneities alter greatly the physical properties of ultimate products, particularly the optical ones, what causes problems in the design of thick and optically perfect materials. The knowledge of the conversion profile and the temperature distribution within the material during the photopolymerization is useful for the process optimization. Unfortunately, these parameters cannot be measured during the process. Thus, we decided to simulate them. Firstly, the necessary parameters (like conversion and reaction rate) were measured on thin material in isothermal conditions by photocalorimetry. Secondly, these kinetic data were used in a computational calculation to obtain the conversion profile and the temperature distribution within dimethacrylate thick material. The calculated temperature and conversion-time curves are in good agreement with the experimental curves determined under the same conditions. 相似文献
976.
Jonas
rtegren Philippe Busson Ulf W. Gedde Anders Hult Anders Eriksson Mikael Lindgren Per-Otto Arntzn David S. Hermann Per Rudquist Sven T. Lagerwall 《Macromolecular Symposia》1999,148(1):179-195
Highly oriented pyroelectric liquid-crystalline polymers were prepared by photopolymerization under the influence of a static electric field from binary mixtures of two acrylate monomers exhibiting chiral smectic C mesomorphism. Both monomers contained nitro groups to yield second order nonlinear optical properties (second harmonic generation) and one of the monomers had two functional groups to yield a crosslinked polymer. The room temperature second order nonlinear susceptibility of the polymers showed during the first two hours a 10 % decrease after which it remained constant during the next 48 days. At elevated temperatures there was a significant difference in the nonlinear optical properties over time between crosslinked and uncrosslinked polymers. The uncrosslinked polymer showed a pronounced loss of second order nonlinear optical activity with time at ≥38°C. The crosslinked polymer showed a much smaller and basically a temperature independent decrease rate in the second order nonlinear optical properties at all the ageing temperatures (23-130°C). Both the loss in mesogen order parameter, very evident for the uncrosslinked polymer, and conformational changes occurring within the mesogens (β mechanism), may account for the observations made. 相似文献
977.
Romain Mougeot Philippe Jubault Julien Legros Thomas Poisson 《Molecules (Basel, Switzerland)》2021,26(23)
Herein, we report a continuous flow process for the synthesis of 2,6-diisopropylphenol—also known as Propofol—a short-acting intravenous anesthesia, widely used in intensive care medicine to provide sedation and hypnosis. The synthesis is based on a two-step procedure: a double Friedel–Crafts alkylation followed by a decarboxylation step, both under continuous flow. 相似文献
978.
Maxwell W. Terban Alexander M. Pütz Gökcen Savasci Ute Heinemeyer Bernd Hinrichsen Philippe Desbois Robert E. Dinnebier 《Journal of polymer science. Part A, Polymer chemistry》2020,58(13):1843-1866
Investigations of the atomic structures within polyamides started over 80 years ago and continue today. These weakly ordered materials diffract X-rays poorly and typically require postprocessing to obtain idealized samples for structural studies. An important goal remains to develop techniques to study the local structure in its natural state, with atomic resolution, and with sensitivity to subtle changes due to synthesis conditions or other technologically relevant processing procedures. Here, we compare the structures of as-produced, nonoriented polyamide 6 ([C6H11NO] n) from both hydrolytic and anionic processes. A total scattering pair distribution function approach is used to elucidate information about the atomic bonding, molecular conformation, chain packing, crystallite size, and ratio of ordered to disordered domain content. The results are compared with those from standard analytical methods. 相似文献
979.
980.
Dr. Ian M. Riddlestone Philippe Weis Dr. Arthur Martens Marcel Schorpp Dr. Harald Scherer Prof. Dr. Ingo Krossing 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(45):10546-10551
Upon coordinating P4 to electron poor cyclopentadienyl-iron cations, the average P−P bond distances shrink and the respective P4 breathing mode in the Raman spectra (600 cm−1, P4, free) is blueshifted by >40 cm−1 in [CpFe(CO)(L)(η1-P4)]+ cations (L=CO or PPh3). Analysis suggests that this corresponds to an umpolung of the bonding from more phosphidic in the known, electron-rich systems to more phosphonium-like in the reported electron-poor versions. This may open new functionalization pathways for white phosphorus P4. 相似文献