共查询到20条相似文献,搜索用时 46 毫秒
1.
Katarzyna Stadnicka Pawe Szlachcic 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(3):o129-o131
The reaction of biphenyl‐2,2′‐diol with 1,1,2,2‐tetrakis(bromomethyl)cyclopropane leads to two products, namely a propellane‐type compound and a dispiro‐type compound. The molecular structure of 4,5;6,7‐dibenzo‐3,8,12‐trioxa[8.3.1]propellane has been determined previously by spectroscopic methods. The crystal structure of the dispiro product, 2,7,12,17‐tetraoxa‐3,4:5,6:13,14:15,16‐tetrabenzodispiro[8.1.8.0]nonadecane, C31H26O4, revealed that the conformations of the nine‐membered heterocyclic rings are due to interactions between the π‐electron system of the biphenyl moiety and the lone electron pairs of the ether O atoms, the repulsion of the lone electron pairs of atoms O1⃛O2 and O3⃛O4, and steric interactions between H atoms in ortho positions. The conformations have C1 symmetry and can be described approximately as twist‐boat. 相似文献
2.
3.
Ottorino DeLucchi Arif Datan Aliye Altunda Fabrizio Fabris Metin Balci 《Helvetica chimica acta》2004,87(9):2364-2367
An efficient synthetic route to the concave‐shaped, potentially ionophoric syn‐ and anti‐isomers of 5,6,11,12,17,18‐hexahydro‐5,18:6,11:12,17‐triepoxytrinaphthylene ( 4 ) was elaborated. Starting from ‘oxabenzonorbornadiene’ ( 5 ), the stannylated precursor 9 was prepared in three steps, followed by cyclotrimerization catalyzed by copper(I) thiophene‐2‐carboxylate (CuTC) , which afforded 4 in a syn/anti ratio of 5 : 4. 相似文献
4.
5.
6.
校本课程“化学传奇”主要是引导学生阅读化学史文章。校本课程从“化学传奇”升级到“化学阅读”,化学阅读的内容拓展了,阅读形式升级了:由文章阅读升级为视频观看和整本书阅读,阅读的时间由校本课程的课内阅读延伸到课外阅读,阅读时段由校本课程季扩展为高中全学段。学生的阅读活动,也由教师规定阅读内容升级到学生在推荐书目内自主选择性阅读和个性化阅读。 相似文献
7.
8.
9.
10.
11.
The evolution of the universe from the particle to the thinking organism has taken place through self-organization. Chemistry has a major role to play in understanding these processes leading to the generation of complex matter. Chemistry has developed a highly powerful molecular synthetic chemistry, mastering the combination and recombination of atoms into increasingly complex molecules through selective chemical reactions. Supramolecular chemistry is harnessing intermolecular forces for the generation of informed supramolecular systems and processes through supramolecular synthetic chemistry implementing molecular information carried by electromagnetic interactions. Supramolecular chemistry has been actively exploring systems undergoing self-organization, i.e., systems capable of spontaneously generating well-defined functional supramolecular architectures by self-assembly from their components, under the control of interactional molecular recognition events, thus behaving as programmed chemical systems. Molecular chemistry may similarly take advantage of the selectivity of covalent reactions to assemble complex molecular architectures through self-organization processes implementing functional molecular recognition. Supramolecular/non-covalent and molecular/covalent SELF-ORGANIZATION may thus be considered as the ULTIMATE SYNTHETIC CHEMISTRY, whereby chemical objects at both levels are generated on the basis of recognition processes involving either interactional or reactional features. Illustrations from the supramolecular domain will serve as illustrations. Supramolecular entities as well as molecules containing reversible bonds are able to undergo a continuous change in constitution by reorganization and exchange of building blocks. This capability defines a Constitutional Dynamic Chemistry (CDC) on both the molecular and supramolecular levels. CDC introduces a paradigm shift with respect to constitutionally static chemistry. It takes advantage of dynamic constitutional diversity to allow variation and selection and thus leads towards the emergence of adaptive and evolutive chemistry. 相似文献
12.
13.
Yu‐Biao Chen Yao Kang Ye‐Yan Qin Zhao‐Ji Li Jian‐Kai Cheng Yuan‐Gen Yao 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(6):m263-m265
The title compound, [Ag2(NO3)2(C5H5NS)]n, was obtained from the reaction of silver nitrate with bis(4‐pyridyl) disufide (4‐PDS) in a mixture of ethanol and water, which suggests that the disulfide bond of 4‐PDS can be cleaved under mild conditions. The structure of the title compound is a two‐dimensional infinite array in which the asymmetric unit contains two Ag atoms, a pyridinium‐4‐thiolate molecule and two nitrate groups. Each pyridinium‐4‐thiolate molecule acts as a μ4 bridge, linking four Ag atoms, with Ag—S bond distances of 2.4870 (19), 2.5791 (19), 2.5992 (19) and 2.848 (2) Å. The Ag⋯Ag distances lie in the range 2.889 (2)–3.049 (1) Å. 相似文献
14.
15.
Markus Pietsch Martin Nieger Michael Gütschow 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(3):o147-o151
The title compounds, tert‐butyl 6‐benzyl‐2‐(3,3‐diethylureido)‐4,5,6,7‐tetrahydrothieno[2,3‐c]pyridine‐3‐carboxylate, C24H33N3O3S, (I), 7‐benzyl‐2‐diethylamino‐5,6,7,8‐tetrahydro‐3‐oxa‐9‐thia‐1,7‐diazafluoren‐4‐one, C20H23N3O2S, (II), and N‐(7‐benzyl‐4‐oxo‐5,6,7,8‐tetrahydro‐4H‐3,9‐dithia‐1,7‐diazafluoren‐2‐yl)benzamide, C23H19N3O2S2, (III), form monoclinic crystal systems. In (I) and (II), the molecules are linked into a three‐dimensional framework by weak intermolecular C—H⋯O=C hydrogen bonds, whereas in (III) stronger intermolecular N—H⋯O=C interactions are observed. The conformation of (I) is further stabilized by an intramolecular N—H⋯O=C hydrogen bond, which effects the planarity of the ureidothiophenecarboxylate moiety. 相似文献
16.
17.
G. Papp Beáta Bugyi Z. Ujfalusi Sz. Halasi J. Orbán 《Journal of Thermal Analysis and Calorimetry》2005,82(1):281-285
Summary The effect of pH was characterised on the thermal stability of magnesium saturated skeletal and cardiac α-actin isoforms with
differential scanning calorimetry (DSC) at pH 7.0 and 8.0. The calorimetric curves were further analysed to calculate the
enthalpy and transition entropy changes. The activation energy was also determined to describe the energy consumption of the
initiation of the thermal denaturation process. Although the difference in Tmvalues is too small to interpret the difference between the a-actin isoforms, the values of the activation energy indicated
that the α-skeletal actin is probably more stable compared to the α-cardiac actin. The difference in the activation energies
indicated that lowering the pH can produce a more stable protein matrix in both cases of the isoforms. The larger range of
the difference in the values of the activation energies suggested that the α-cardiac actin is probably more sensitive to the
change of the pH compared to the α -skeletal actin. 相似文献
18.
19.