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排序方式: 共有195条查询结果,搜索用时 312 毫秒
31.
Guangrong Zheng Sean Parkin Linda P. Dwoskin Peter A. Crooks 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(1):o9-o11
The crystal structures of the title compounds, 2α,4α‐dibenzyl‐3α‐tropanol (2α,4α‐dibenzyl‐8‐methyl‐8‐azabicyclo[3.2.1]octan‐3α‐ol), C22H27NO, (I), and 2α,4α‐dibenzyl‐3β‐tropanol (2α,4α‐dibenzyl‐8‐methyl‐8‐azabicyclo[3.2.1]octan‐3β‐ol), C22H27NO, (II), show that both compounds have a piperidine ring in a chair conformation and a pyrrolidine ring in an envelope conformation. Isomer (I) is asymmetric, the benzyl groups having different orientations, whereas isomer (II) is mirror symmetric, and the N and O atoms, the C atom attached to the hydroxy group, and the methyl C atom attached to the N atom lie on the mirror plane. In the crystal structures of both (I) and (II), the molecules are linked together by intermolecular O—H⋯N hydrogen bonds to form chains that run parallel to the a direction in (I) and parallel to b in (II). 相似文献
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Xanthan sulfuric acid is an efficient solid acid catalyst for the preparation of 2‐aryl benzimidazoles in excellent yields. This method is applicable for the reaction of benzo[c][1,2,5]thiadiazole‐4,5‐diamine with aldehydes by simple physical grinding at room temperature. The salient features of the present methodology is cheaper process, easy synthesis of stable catalyst and the catalyst can be easily recycled without significant loss of activity. 相似文献
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A central endeavor of thermodynamics is the measurement of free energy changes. Regrettably, although we can measure the free energy of a system in thermodynamic equilibrium, typically all we can say about the free energy of a nonequilibrium ensemble is that it is larger than that of the same system at equilibrium. Herein, we derive a formally exact expression for the probability distribution of a driven system, which involves path ensemble averages of the work over trajectories of the time-reversed system. From this we find a simple near-equilibrium approximation for the free energy in terms of an excess mean time-reversed work, which can be experimentally measured on real systems. With analysis and computer simulation, we demonstrate the accuracy of our approximations for several simple models. 相似文献
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Vijayakumar N. Sonar Sean Parkin Peter A. Crooks 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(8):o547-o549
The title compound, C16H12Cl2N2, crystallizes in the centrosymmetric space group P21/c. Two independent but chemically identical molecules comprise the asymmetric unit and in each of these the pyrazole ring is planar. 相似文献
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