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991.
Carboxylic acids are conveniently and efficiently protected as their p-methoxybenzyl esters under very mild conditions using the pre-formed reagent N,N-diisopropyl-O-(4-methoxybenzyl)isourea, and this method allows selective protection of carboxylic acids in the presence of other functionalities such as enolisable ketones and alcohol groups. 相似文献
992.
Three new compounds based on carbazole planar skeleton were synthesised. Among them there is a new ligand and a potential DNA intercalator which contains a benzothiazolium moiety connected to the carbazole ring by a vinyl bridge. The absorption and emission spectral properties of this new ligand have been studied by spectroscopic methods. 相似文献
993.
Muriel Sanchez Ousmane Diallo Adyl Oussaid Boualem Oussaid Bernard Garrigues 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):235-242
Abstract The syntheses of organometallics such as alkyllithium compounds are performed. Furan and thiophene derivatives were prepared. Parameters which influence the yield have been optimized. The more important were the physical states of lithium and its sodium content and the nature of the substrate. 相似文献
994.
995.
We have shown in preceding papers(1–3), in a study of some specific anilinium ions such as φNH+ 3-n (CH3)n, φ2NH+ 2 and φ3NH+, that varying the ammonium groups, or the medium, can lead to great changes in the intensity of the secondary transition of the chromophore(1–4) because of a δ, π coupling involving the substituent (1–10) and φ. In the present work we should like to extend our experiments to more complex ions - since apart our own works the UV spectroscopy of the aniliniums is almost unknown - to study the sensitivity of the chromophore to long range interactions with X through space or through the bonds of the substituents(11–16). 相似文献
996.
Catherine Bianchi Bruno Grassl Bernard Franois Christine Dagron‐Lartigau 《Journal of polymer science. Part A, Polymer chemistry》2005,43(19):4337-4350
Water‐soluble and photoluminescent block copolymers [poly(ethylene oxide)‐block‐poly(p‐phenylene vinylene) (PEO‐b‐PPV)] were synthesized, in two steps, by the addition of α‐halo‐α′‐alkylsulfinyl‐p‐xylene from activated poly(ethylene oxide) (PEO) chains in tetrahydrofuran at 25 °C. This copolymerization, which was derived from the Vanderzande poly(p‐phenylene vinylene) (PPV) synthesis, led to partly converted PEO‐b‐PPV block copolymers mixed with unreacted PEO chains. The yield, length, and composition of these added sequences depended on the experimental conditions, namely, the order of reagent addition, the nature of the monomers, and the addition of an extra base. The addition of lithium tert‐butoxide increased the length of the PPV precursor sequence and reduced spontaneous conversion. The conversion into PPV could be achieved in a second step by a thermal treatment. A spectral analysis of the reactive medium and the composition of the resulting polymers revealed new evidence for an anionic mechanism of the copolymerization process under our experimental conditions. Moreover, the photoluminescence yields were strongly dependant on the conjugation length and on the solvent, with a maximum (70%) in tetrahydrofuran and a minimum (<1%) in water. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4337–4350, 2005 相似文献
997.
We study two types of generalized Baxter–Wu models, by means of transfer-matrix and Monte Carlo techniques. The first generalization allows for different couplings in the up- and down-triangles, and the second generalization is to a q-state spin model with three-spin interactions. Both generalizations lead to self-dual models, so that the probable locations of the phase transitions follow. Our numerical analysis confirms that phase transitions occur at the self-dual points. For both generalizations of the Baxter–Wu model, the phase transitions appear to be discontinuous. 相似文献
998.
999.
1000.
The ethylidene acetal of d-erythrose was used as a template for stereoselective IMDA reactions: high endo selectivity and yields in favor of the cis product were observed with 1,3,9-trienes, resulting from a boat transition state. For natural product synthesis, the reaction was successfully applied to a diene with terminal Z-olefin. 相似文献