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Rotation of Asymmetric Top01:11

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By definition, a spherically symmetric body has the same moment of inertia about any axis passing through its center of mass. This situation changes if there is no spherical symmetry. Since most rigid bodies are not spherically symmetric, these require special treatment.
The relationship between the angular momentum of any rigid body and its angular velocity, both of which are vectors, involves the moment of inertia. The moment of inertia is a scalar quantity only for spherically symmetric...
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Biological membranes show uneven distribution of different types of lipids in the inner and outer layers, resulting in transverse asymmetric membranes. The treatment of the erythrocyte membrane with the enzyme phospholipase confirmed the asymmetric nature of the lipid bilayer. The enzyme hydrolyzes lipids into fatty acids and hydrophilic groups. The phospholipase acts only on the outer layer of the membrane, while the inner layer remains intact. The phospholipase treatment resulted in 80%...
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A phase diagram combines plots of pressure versus temperature for the liquid-gas, solid-liquid, and solid-gas phase-transition equilibria of a substance. These diagrams indicate the physical states that exist under specific conditions of pressure and temperature and also provide the pressure dependence of the phase-transition temperatures (melting points, sublimation points, boiling points). Regions or areas labeled solid, liquid, and gas represent single phases, while lines or curves represent...
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Intramolecular Claisen Condensation of Dicarboxylic Esters: Dieckmann Cyclization01:13

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Dieckmann cyclization is an intramolecular Claisen condensation of diesters. The reaction occurs in the presence of a base and generates a cyclic β-ketoester as the final product. Commonly, 1, 6 and 1, 7-diesters are preferred substrates for the reaction since the generated five, and six-membered cyclic β-keto esters are particularly more stable.
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Phase Transitions

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Whether solid, liquid, or gas, a substance's state depends on the order and arrangement of its particles (atoms, molecules, or ions). Particles in the solid pack closely together, generally in a pattern. The particles vibrate about their fixed positions but do not move or squeeze past their neighbors. In liquids, although the particles are closely spaced, they are randomly arranged. The position of the particles are not fixed—that is, they are free to move past their neighbors to...
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Reduction of Alkenes: Asymmetric Catalytic Hydrogenation

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Catalytic hydrogenation of alkenes is a transition-metal catalyzed reduction of the double bond using molecular hydrogen to give alkanes. The mode of hydrogen addition follows syn stereochemistry.
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对非对称循环的离子相转移催化剂

Hiromichi Egami1, Tomoki Niwa1, Hitomi Sato1

  • 1School of Pharmaceutical Sciences, University of Shizuoka , 52-1 Yada, Suruga-ku, Shizuoka 422-8526, Japan.

Journal of the American Chemical Society
|February 10, 2018
PubMed
概括
此摘要是机器生成的。

研究人员为不对称化开发了新的二酸前催化剂. 这些催化剂通过一种新的6 - 内循环过程,使化二氧化的有效合成成为可能.

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科学领域:

  • 有机化学
  • 不对称的催化
  • 化化学

背景情况:

  • 像Selectfluor这样的电友化试剂在有机合成中至关重要.
  • 开发高效和选择性的催化方法来引入是一种重大挑战.
  • 阶段转移催化为各种有机转化提供了多功能平台.

研究的目的:

  • 设计和合成用于不对称化的新型二酸前催化剂.
  • 研究这些前催化剂在基因的反选择性化中的催化活性.
  • 探索开发的催化系统的范围和局限性.

主要方法:

  • 基于Selectfluor结构的二酸预催化剂的合理设计.
  • 预催化剂的脱质,以产生离子相移催化剂.
  • 不对称的化反应使用化胺和非循环作为基质.
  • 使用奇拉色谱学和NMR光谱学对异位选择性和异位选择性的分析.

主要成果:

  • 一系列二酸前催化剂被合成和评估.
  • 预催化剂2a在催化胺的6 - 内循环中表现出高效率.
  • 获得的二氧化产品具有优异的反选择性 (高达99% ee).
  • 亚环三替代基反应具有良好的二选择性,而线性二替代基反应具有较低的选择性.

结论:

  • 开发的二酸预催化剂有效地作为非对称化过程中的离子相转移催化剂.
  • 这种6 - 内循环化是合成二氧化的前所未有的转化.
  • 反应机制可能涉及碳酸中间体,为进一步的催化剂开发提供了洞察力.