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991.
Dr. Thanh Binh Nguyen Dr. Tuan Minh Nguyen Dr. Pascal Retailleau 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(21):4682-4689
In this study, a very simple technique to perform efficiently photodimerization of some vinylpyridines is reported. By irradiating a stirred mixture of several stilbazoles with solid oxalic acid dihydrate dispersed in a nonpolar (i.e., cyclohexane) or moderately polar (benzene, dichloromethane, dioxane) solvent, the corresponding dimeric cyclobutane adducts were obtained in high yields and excellent regio- and stereoselectivities. The strategy could also be applied successfully to oily, waxy, or even insoluble stilbazoles. Moreover, the oxalic acid loading could be lowered to substoichiometric amounts. When further optimizations were needed, our strategy was found to be highly flexible to identify other oligocarboxylic acids as alternative additives to improve, or even overturn, the regioselectivity. Oxalic acid and other oligocarboxylic acids were found to be capable of orienting more than 50 stilbazoles toward photodimerization under these conditions. 相似文献
992.
Woo‐Jin Yoo Junpei Kondo Jos A. Rodríguez‐Santamaría Thanh V. Q. Nguyen Sh Kobayashi 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(20):6844-6847
A facile synthetic procedure for the preparation of α‐trifluoromethyl carboxylic acids and esters was achieved through multicomponent coupling reactions between gem‐difluoroalkenes, cesium fluoride, and carbon dioxide. The products were generated in moderate to excellent yields, and the synthetic utility of this method was demonstrated through the preparation of trifluoromethylated versions of popular nonsteroidal anti‐inflammatory drugs (NSAIDs). 相似文献
993.
Analytical expressions of the exciton-exciton interaction in 3D and 2D laser-excited semiconductors are approximately derived in rather easy-to-handle forms which enable us to study in detail their dependences on the exciton momenta, the momentum transferred between two excitons and the electron-hole mass ratio.We would like to thank Prof. Nguyen Van Hieu and Prof. Dao Vong Due for their support given to us in the research of highly excited media. 相似文献
994.
M. Wintenberger J. Dugue M. Guittard Nguyen Huy Dung Vo Van Tien 《Journal of solid state chemistry》1987,70(2)
The two isomorphous compounds LaCrOS2 and LaCrOSe2 are ferromagnetic (Tc = 35 and 51 K, respectively). This implies ferromagnetic super-superexchange interactions. NdCrOS2 is antiferromagnetic (TN = 72 K) and undergoes a spin-flop transition (Hc = 54 KOe at 20 K). The study of the thermal variation of Cr3+ and Nd3+ magnetic moments below TN allows a rough estimate of the Cr---Nd and Cr---Cr exchange fields ratio (0.1). 相似文献
995.
The 1,3-dipolar cycloreversion pathway of the pentazole anion (N5?) to the azide anion (N3?) plus dinitrogen (N2) has been investigated using ab initio methods. At the MP4SDQ/6–31 + G* level of theory plus zero-point energy contributions, the pentazole anion is predicted to lie at 31 kcal mol?1 above the N3? + N2 system but the energy barrier for decomposition is 22 kcal mol?1. This indicates that the pentazole anion could be isolated in an inert matrix at low temperature. Comparison between extended Hückel calculations on the (N5)M(CO)3 and (C5H5)M(CO)3 complexes (with M = Fe2+, Mn+ and Cr) suggests that the N5? complexes would be formed if the fragments could be brought together. Predicted vibrational frequencies of the N5? anion are also reported. 相似文献
996.
997.
Nguyen Ngoc Chan 《Czechoslovak Journal of Physics》1988,38(6):666-671
Using the method of double-time retarded Green function, an expression for the spin energy spectrum including the contributions of one-phonon and two-phonon processes has been derived. Calculations have been performed using the spin wave approximation. The broadening of the energy level is roughly estimated in a peculiar case.I would like to thank Dr. Dagmat Fraitová for her advice and help. 相似文献
998.
Nguyen Ba Chanh Christian Hauw Alain Meresse Madeleine Rey-Lafon Laure Ricard 《Journal of Physics and Chemistry of Solids》1985,46(12):1413-1420
The existence of three main crystalline phases (called III, II and I) in (C12H25NH3)2CdCl4 has been revealed by differential scanning calorimetry. X-ray diffraction and spectroscopic studies. The crystal- lographic evolution with increasing temperature appears to be monoclinic (III) → orthorhombic (II) → tetragonal (I). The low temperature phase III is the only ordered structure. The phase transition (III-II), which is of first order type, corresponds to an order-disorder mechanism involving the organic part of the structure (alkylammonium chains) whereas the phase transition (II-I), which is of second-order type, is related to the arrangement of the mineral matrix (octahedra of perovskite layers). An intermediate disordered form II', stable in a very narrow temperature range and structurally similar to the form II, has also been observed, so that the transformation (III-II) proceeds, in fact, in two steps (III-II'-II). The variation enthalpies observed at the transitions (III-II'-II) and analyzed through an order-disorder mechanism demonstrate the high disorder of the alkylammonium chains in form II, in agreement with spectroscopic results. No thermal anomaly or spectroscopic modification is observed for the high temperature transition (II-I). 相似文献
999.
X-ray photoelectron spectroscopy (XPS) technique have been used to investigate the interface formed between poly(2-methoxy-5-(2′-ethyl-hexyloxyl)-p-phenylene vinylene) (MEH-PPV) and indium tin oxide (ITO) layer in top emission organic light emitting diodes. A weak but noticeable diffusion of indium into the polymer film was observed. Interactions between the diffused metallic atoms with the polymer resulted in the formation of carbon-metal complexes at the interface region. Compared to the ITO/MEH-PPV interface, the penetration of indium into the polymer layer was less important and may be explained by the surface morphology of the polymer film. It was however, a probable factor for fast degradation of devices using this structure. 相似文献
1000.
Anh-Tuan Le Chong-Oh Kim Nguyen Chau Nguyen Duy Cuong Nguyen Duc Tho Nguyen Quang Hoa Heebok Lee 《Journal of magnetism and magnetic materials》2006
In this paper, the effect of microstructural and surface morphological developments on the soft magnetic properties and giant magneto-impedance (GMI) effect of Fe73.5−xCrxSi13.5B9Nb3Au1 (x=1, 2, 3, 4, 5) alloys was investigated. It was found that the Cr addition causes slight decrease in the mean grain size of α-Fe(Si) grains. AFM results indicated a large variation of surface morphology of density and size of protrusions along the ribbon plane due to structural changes caused by thermal treatments with increasing Cr content. Ultrasoft magnetic properties such as the increase of magnetic permeability and the decrease of coercivity were observed in the samples annealed at 540 °C for 30 min. Accordingly, the GMI effect was also observed in the annealed samples. 相似文献