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相关概念视频

Woodward–Hoffmann Selection Rules and Microscopic Reversibility01:34

Woodward–Hoffmann Selection Rules and Microscopic Reversibility

3.1K
Electrocyclic reactions, cycloadditions, and sigmatropic rearrangements are concerted pericyclic reactions that proceed via a cyclic transition state. These reactions are stereospecific and regioselective. The stereochemistry of the products depends on the symmetry characteristics of the interacting orbitals and the reaction conditions. Accordingly, pericyclic reactions are classified as either symmetry-allowed or symmetry-forbidden. Woodward and Hoffmann presented the selection criteria for...
3.1K
Chair Conformation of Cyclohexane02:02

Chair Conformation of Cyclohexane

14.6K
The chair conformation is the most stable form of cyclohexane due to the absence of angle and torsional strain. The absence of angle strain is a result of cyclohexane’s bond angle being very close to the ideal tetrahedral bond angle of 109.5° in its chair conformer. Similarly, the torsional strain is also absent owing to the perfectly staggered arrangement of bonds.
The hydrogen atoms linked to carbons are arranged in two different axial and equatorial orientations to achieve this...
14.6K
Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal Electrocyclic Reactions: Stereochemistry

2.0K
The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
2.0K
Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

2.3K
Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
2.3K
¹H NMR of Conformationally Flexible Molecules: Temporal Resolution00:52

¹H NMR of Conformationally Flexible Molecules: Temporal Resolution

839
At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the...
839
Stereoisomerism of Cyclic Compounds02:33

Stereoisomerism of Cyclic Compounds

8.9K
In this lesson, we delve into the role of ring conformation and its stability, which determines the spatial arrangement and, consequently, the molecular symmetry and stereoisomerism of cyclic compounds. 1,2-Dimethylcyclohexane is used as a case study to evaluate the possible number of stereoisomers. Here, given the multiple (n = 2) chiral centers, there are 2n = 4 possible configurations that lack a plane of symmetry, as the ring skeleton exists in a non-planar chair conformation. In addition,...
8.9K

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相关实验视频

Updated: Jul 1, 2025

High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal
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High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal

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改变液晶螺旋曲线,使用可逆的罗塔开关.

Sujun Chen1, Nathalie Katsonis2, David A Leigh1,3

  • 1School of Chemistry and Molecular Engineering, East China Normal University, Shanghai, 200062, P. R. China.

Angewandte Chemie (International ed. in English)
|March 6, 2024
PubMed
概括

研究人员展示了如何改变一个分子 (rotaxane) 的奇拉性,从而动态地改变液晶的度. 这在软物质系统中将分子奇拉性与宏观性质联系起来.

关键词:
机械结合物 机械结合物罗塔克桑的使用方法柔软的物质 软的物质立体化学是一种立体化学.

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Last Updated: Jul 1, 2025

High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal
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Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets
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科学领域:

  • 超分子化学 超分子化学
  • 软物质物理学 软物质物理学
  • 奇拉性研究 奇拉性研究

背景情况:

  • 在生物学和人工系统中,了解跨不同长度尺度的奇拉信息传输是一个重大挑战.
  • 在分子和宏观系统中模仿和控制奇拉性仍然是活跃的研究领域.

研究的目的:

  • 为了证明罗塔分子中的动态性变化的转导到软物质系统中的宏观变化.
  • 研究分子性影响大规模结构的机制.

主要方法:

  • 利用一个具有可移动宏循环和轴上的点性拉中心的轮素分子.
  • 研究了宏循环位置对分子和宏观水平上性表达的影响.
  • 观察了罗性阴性液晶相的音距长度的变化.

主要成果:

  • 在轮轴上移动宏循环动态地改变了奇拉信息的表达.
  • 这种分子水平的奇拉性变化成功地传递到宏观尺度.
  • 观察到,合性阴性液晶结构的音距长度发生了显著的变化.

结论:

  • 这项研究成功地证明了通过分子设计对宏观度的动态控制.
  • 罗塔系统可以作为多个长度尺度的奇拉信息的有效传感器.
  • 这项工作为通过分子级别的性切换控制软物质特性提供了洞察力.