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相关概念视频

[3,3] Sigmatropic Rearrangement of 1,5-Dienes: Cope Rearrangement01:21

[3,3] Sigmatropic Rearrangement of 1,5-Dienes: Cope Rearrangement

2.8K
The Cope rearrangement is classified as a [3,3] sigmatropic shift in 1,5-dienes, leading to a more stable, isomeric 1,5-diene. The reaction involves a concerted movement of six electrons, four from two π bonds and two from a σ bond, via an energetically favorable chair-like transition state.
2.8K
Polymer Classification: Stereospecificity01:26

Polymer Classification: Stereospecificity

2.5K
Polymerization generates chiral centers along the entire backbone of a polymer chain. Accordingly, the stereochemistry of the substituent group has a significant effect on polymer properties. Polymers formed from monosubstituted alkene monomers feature chiral carbons at every alternate position in the polymer backbone. Relative to the predominant orientation of substituents at the adjacent chiral carbons, the polymer can exist in three different configurations: isotactic, syndiotactic, and...
2.5K
Thermal Sigmatropic Reactions: Overview01:16

Thermal Sigmatropic Reactions: Overview

2.1K
Sigmatropic rearrangements are a class of pericyclic reactions in which a σ bond migrates from one part of a π system to another. These are intramolecular rearrangements where the total number of σ and π bonds remain unchanged.
Sigmatropic shifts are classified based on an order term [i, j ], where i and j indicate the number of atoms across which each end of the σ bond migrates. Below are examples of a [3,3] sigmatropic shift in...
2.1K
Cycloaddition Reactions: MO Requirements for Thermal Activation01:16

Cycloaddition Reactions: MO Requirements for Thermal Activation

3.6K
Thermal cycloadditions are reactions where the source of activation energy needed to initiate the reaction is provided in the form of heat. A typical example of a thermally-allowed cycloaddition is the Diels–Alder reaction, which is a [4 + 2] cycloaddition. In contrast, a [2 + 2] cycloaddition is thermally forbidden.
3.6K
Aryldiazonium Salts to Azo Dyes: Diazo Coupling01:11

Aryldiazonium Salts to Azo Dyes: Diazo Coupling

3.0K
The reaction of weakly electrophilic aryldiazonium (also called arenediazonium) salts with highly activated aromatic compounds leads to the formation of products with an —N=N— link, called an azo linkage. This reaction, presented in Figure 1, is known as diazo coupling and occurs without the loss of the nitrogen atoms of the aryldiazonium salt. Highly activated aromatic compounds such as phenols or arylamines favor the diazo coupling reaction. The coupling generally occurs at the...
3.0K
Polymer Classification: Crystallinity01:21

Polymer Classification: Crystallinity

2.9K
Unlike ionic or small covalent molecules, polymers do not form crystalline solids due to the diffusion limitations of their long-chain structures. However, polymers contain microscopic crystalline domains separated by amorphous domains.
Crystalline domains are the regions where polymer chains are aligned in an orderly manner and held together in proximity by intermolecular forces. For example, chains in the crystalline domains of polyethylene and nylon are bound together by van der Waals...
2.9K

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相关实验视频

Updated: Jul 25, 2025

High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal
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在一个具有可切换固态行为的多功能化化合物中,巨大的无otropic热膨胀.

Xiaodan Ding1, Daniel K Unruh1, Liulei Ma1

  • 1Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409, USA.

Angewandte Chemie (International ed. in English)
|June 27, 2023
PubMed
概括

研究人员开发了一种具有巨大的有机化合物,异型热膨胀 (TE). 该材料显示可切换的TE行为,为先进的固态材料提供新的设计策略.

关键词:
不同类型的热膨胀亚化合物 亚化合物晶体工程 晶体工程固态运动 固态运动可切换的行为.

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科学领域:

  • 材料科学 材料科学 材料科学
  • 固态化学 固态化学
  • 有机化学 有机化学

背景情况:

  • 在固态材料中实现显著的异构热膨胀 (TE) 是很困难的,因为加热时体积膨胀的趋势.
  • 不同类型的TE对于需要与温度变化的方向维度变化的应用至关重要.

研究的目的:

  • 设计和描述一种新型有机化合物,其呈现巨大且可切换的异性热膨胀.
  • 研究不同温度状态下不同热膨胀行为背后的机制.

主要方法:

  • 一种有机化合物的合成,具有两个基.
  • 在各种温度范围内详细描述热膨胀特性.
  • 固态核磁共振 (NMR) 光谱检测分子运动.
  • 热力学分析与固态运动相关的和变化.

主要成果:

  • 合成的有机晶体在高温下表现出巨大的异构性TE (α=211 M K-1),具有零面积TE和显著的线性膨胀.
  • 在低温下,在所有方向观察到中度正 TE.
  • 显著的热力学形状和固态NMR证据证实了温度依赖的动态运动.
  • 观察到的热膨胀行为和固态运动在循环时被发现是完全可逆的.

结论:

  • 该研究提出了一种成功的策略,用于在固态材料中实现巨大且可切换的异性热膨胀.
  • 这些发现突出了功能性有机化合物中动态分子运动的潜力,用于量身定制的TE反应.
  • 这项工作为设计具有可控制的尺寸稳定性的先进材料为各种技术应用开辟了道路.