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991.
992.
Albert Lévai 《Monatshefte für Chemie / Chemical Monthly》1991,122(8-9):691-695
Summary Reactions of 3-arylidenechromanones (1 – 4) and -1-thiochromanones (5 – 8) with thiourea gave thiazines (9 – 16) under acidic and pyrimidine derivatives (17 – 21) under alkaline reaction conditions
Kondensierte Heterocyclen, VI: Umsetzungen von 3-Arylidenchromanonen und-1-thiochromanonen mit Thioharnstoff
Zusammenfassung Die Umsetzung von 3-Arylidenchromanonen1 – 4 und -1-thiochromanonen5 – 8 mit Thioharnstoff liefert unter sauren Bedingungen die Thiazine9 – 16 und in basischem Milieu die Pyrimidine17 – 21.相似文献
993.
Koichiro Fukuda Miyuki Hisamura Nobuyuki Tera 《Journal of solid state chemistry》2007,180(6):1809-1815
A new quaternary layered carbide, Zr2[Al3.56Si0.44]C5, has been synthesized and characterized by X-ray powder diffraction, transmission electron microscopy and thermopower and electrical conductivity measurements. The crystal structure was successfully determined using direct methods, and further refined by the Rietveld method. The crystal is trigonal (space group R3m, Z=3) with lattice dimensions of a=0.331059(5), c=4.09450(5) nm and V=0.38864(1) nm3. The final reliability indices calculated from the Rietveld refinement were Rwp=6.24%, Rp=4.21% and RB=0.82%. The crystal structure is composed of electroconductive NaCl-type ZrC slabs separated by Al4C3-type [Al3.56Si0.44]C3 layers. This material had thermoelectric properties superior to those of the ternary layered carbides Zr2Al3C4 and Zr3Al3C5, with the power factor reaching 7.6×10−5W m−1 K−2. 相似文献
994.
K. V. Zaitsev S. S. Karlov M. V. Zabalov A. V. Churakov G. S. Zaitseva D. A. Lemenovskii 《Russian Chemical Bulletin》2005,54(12):2831-2840
Titanatrane CpTi(OCH(CH3)CH2)3N (3) was prepared by the reaction of CpTiCl3 with N(CH2CH(CH3)OH)3 in the presence of triethylamine. The reaction of CpTi(OMe)3 (8) with N(CH2CH2OH)2(CH2CHPhOH), erythro-N(CH2CH2OH)2(CHPhCHPhOH), and N(CH2CH2OH)2(CH2CPh2OH) gave cyclopentadienyltitanatranes 12–14. Compound 8 reacts with threo-N(CH2CH2OH)2(CHPhCHPhOH) to give a mixture of threo-CpTi(OCH2CH2)2(OCHPhCHPh)N and threo-MeOTi(OCH2CH2)2(OCHPhCHPh)N. Slow hydrolysis of the latter product gave threo-[Ti3O(OMe){(OCH2CH2)2− (OCHPhCHPh)N} 3]2, which was studied by X-ray diffraction analysis. The crystal structures of 3 and 12 were also determined by X-ray diffraction analysis. The titanium coordination polyhedron in these complexes is a distorted
trigonal bipyramid in which the equatorial positions are occupied by three oxygen atoms and the axial positions contain the
N atom and the Cp group. The titanium—nitrogen distances (2.313(2), 2.291(2) Å in two independent molecules of 3 and 2.271(2) Å in compound 12) confirm the presence of Ti←N transannular interaction.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2736–2744, December, 2005. 相似文献
995.
E. Yu. Mikhteeva E. G. Savchuk E. A. Tararako E. B. Merkulov V. K. Goncharuk 《Journal of Structural Chemistry》2005,46(6):1082-1085
Images of cleaved surfaces were obtained for 53ZrF4-20BaF2-4LaF3-3AlF3-20NaF (ZBLAN) glasses and fused quartz using an NTMDT atomic force microscope. It is shown that the scatter of particle size depends on the cooling rate and is 21–48.5 Å for the cleaved surface of ZBLAN glass obtained by very fast cooling and 68–172 Å for the cleaved surface of ZBLAN after slow cooling. For cleaved fused quartz, the range is 25-18 Å. 相似文献
996.
Paavo?Mansikkam?ki Manu?Lahtinen Kari?RissanenEmail author 《Cellulose (London, England)》2005,12(3):233-242
The completeness of mercerisation can be evaluated by investigating the changes in the crystalline regions of cellulose from
cellulose I (C-I) to cellulose II (C-II) by the X-ray powder diffraction method. Mercerisation experiments in four different
solution systems: ethanol/water, acetone, DMSO and xylene, are reported. Also the effect of some additives, external pressure,
treatment time and alkalisation temperature were studied. In two-phase solvent systems, structural changes of cellulose crystallites
depended primarily on the distribution and solubility of sodium hydroxide in the solvent phases. The sodium hydroxide concentration
in the hydrophilic phase must exceed 7–8 w/w-% before complete crystal change from C-I to C-II can occur. The precipitation
of sodium hydroxide due to high concentration prevents the successful use of one-phase ethanol/water system in slurry process.
On the contrary, the 2-propanol/water/sodium hydroxide system separates into two layers; to the water-rich lower layer and
the 2-propanol-rich upper layer, where the sodium hydroxide remains mainly in the water-rich lower layer. This prevents the
precipitation of sodium hydroxide and promotes the alkalisation of cellulose. Ammonium chloride and ammonium hydroxide clearly
had a positive effect by promoting the crystal changes, however, the urea concentration used in this study was obviously too
small. In the advantageous two-phase 2-propanol/water systems, the alkalisation time was only 15 min when the treatment temperature
was kept between 0 and 10 °C. Reduced external pressure was found to have a small but still detectable positive effect on
cellulose alkalisation while over-pressure prevented crystal changes. 相似文献
997.
Boris GuintchinStefan Bienz 《Tetrahedron》2003,59(38):7527-7533
Enantiomerically enriched (E)- and (Z)-configured α-acetoxyallylsilanes have been prepared starting from a chiral acylsilane bearing an asymmetric unit at the silicon portion. Treatment of these compounds with organocuprates afforded the respective vinylogous substitution products in high yields and high stereoselectivities. The transformations proceed essentially by complete anti attack of the nucleophiles to the allylic acetates and predominantly via transition states leading to the (E)-configured vinylsilane products. By the proper choice of the double bond geometry in the starting material, the configuration of the newly formed stereogenic center can be controlled. The method represents a new and flexible entry into chiral vinylsilanes that can be used for subsequent transformations. As an example, the α,β-unsaturated γ-chiral, naturally occurring ketone (S)-(+)-bishomomanicone was synthesized with this method, which represents the first synthetic access to this compound. 相似文献
998.
999.
Titanosilicates with complete or partial substitution of Ge or Nb in the framework and having the mineral pharmacosiderite topology were hydrothermally prepared and their ion-exchange properties towards Cs were studied for Ti/Ge/Si, Ti/Si, Nb/Ti/Si and pure Ge phases. The basis for the differences in the ion exchange properties measured as distribution coefficients (Kd) for these materials are detailed via structural characterization using the Rietveld refinement technique on the X-ray powder diffraction data. The differences in affinity towards Cs+ result either from the degree of hydration of the exchanger resulting in different coordination environments or the position of cesium ion in the eight-ring channel. 相似文献
1000.
本文发现6~40号元素对能量为20keV的X_射线的质量吸收系数和质量相干散射系数之间呈二次幂函数关系,并据此提出了X_射线荧光定量分析校正基体效应的新方法——RhKa相干散射平方法.用国家标准物质GBW对该原理进行了验证.本法用于硅酸盐地质样品中微量元素的测定取得令人满意的结果. 相似文献