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Predicting Reaction Outcomes02:24

Predicting Reaction Outcomes

8.7K
Kinetics describes the rate and path by which a reaction occurs. In contrast, thermodynamics deals with state functions and describes the properties, behavior, and components of a system. It is not concerned with the path taken by the process and cannot address the rate at which a reaction occurs. Although it does provide information about what can happen during a reaction process, it does not describe the detailed steps of what appears on an atomic or a molecular level. On the other hand,...
8.7K
Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal Electrocyclic Reactions: Stereochemistry

2.1K
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.
2.1K
Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

1.9K
The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
1.9K
Stereochemical Effects of Enolization01:12

Stereochemical Effects of Enolization

2.2K
The chiral α-carbon of the carbonyl compound is the stereocenter of the molecule. As shown in the figure below, when such a carbonyl compound undergoes racemization under an acidic or basic condition, an achiral enol is formed.
2.2K
Woodward–Hoffmann Selection Rules and Microscopic Reversibility01:34

Woodward–Hoffmann Selection Rules and Microscopic Reversibility

3.3K
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...
3.3K
Diels–Alder vs Retro-Diels–Alder Reaction: Thermodynamic Factors01:31

Diels–Alder vs Retro-Diels–Alder Reaction: Thermodynamic Factors

5.3K
The Diels–Alder reaction is thermally reversible, meaning that the reaction reverts to the starting diene and dienophile under suitable temperatures. The forward reaction gives a cyclohexene derivative and is favored at low to medium temperatures. The reverse process, also called retro-Diels–Alder reaction, is a ring-opening process favored at high temperatures.
5.3K

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相关实验视频

Updated: Sep 18, 2025

Unraveling Entropic Rate Acceleration Induced by Solvent Dynamics in Membrane Enzymes
09:42

Unraveling Entropic Rate Acceleration Induced by Solvent Dynamics in Membrane Enzymes

Published on: January 16, 2016

9.1K

动力学,热力学和立体编辑反应的出现.

Gino Occhialini1, Alison E Wendlandt1

  • 1Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.

Accounts of chemical research
|June 26, 2025
PubMed
概括

研究人员为有机化学开发了新的立体中心编辑工具,使得立体同位素的选择性相互转换成为可能. 这些方法使用光氧化催化和基质中间体来精确控制分子配置.

科学领域:

  • 有机化学 有机化学
  • 立体化学是一种立体化学.
  • 催化剂是一种催化剂.

背景情况:

  • 立体异构体的选择性形成是有机合成的一个主要挑战.
  • 立体化学通常在键形成过程中固定,限制了访问复杂分子的灵活性.
  • 对合成后的立体化学进行修订,为从可访问的前体中获得更具挑战性的目标提供了一条途径.

研究的目的:

  • 开发立体中心编辑工具,以实现立体同位素的可预测和可调节的相互转换.
  • 为了利用激素中间体和光反氧化催化剂,实现轻度和高效的立体编辑.
  • 将这些方法应用于具有挑战性的合成问题,包括罕见糖合成和三级立体中心修订.

主要方法:

  • 使用顺序的原子抽象和通过激素中间体捐赠的步骤.
  • 在温和的条件下使用光氧催化剂产生活性基.
  • 研究催化剂控制以实现失衡,动力控制的产品分布.

主要成果:

  • 开发了二次酒精立体中心的立体编辑方法,使可调节的站点和立体控制.
  • 将立体编辑扩展到未激活的三级立体中心,提供新的合成灵活性.
  • 在罕见糖合成和构成性异构化,包括异构化中的应用.

更多相关视频

Coulomb Explosion Imaging as a Tool to Distinguish Between Stereoisomers
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Coulomb Explosion Imaging as a Tool to Distinguish Between Stereoisomers

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Real-time Monitoring of Reactions Performed Using Continuous-flow Processing: The Preparation of 3-Acetylcoumarin as an Example
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Real-time Monitoring of Reactions Performed Using Continuous-flow Processing: The Preparation of 3-Acetylcoumarin as an Example

Published on: November 18, 2015

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相关实验视频

Last Updated: Sep 18, 2025

Unraveling Entropic Rate Acceleration Induced by Solvent Dynamics in Membrane Enzymes
09:42

Unraveling Entropic Rate Acceleration Induced by Solvent Dynamics in Membrane Enzymes

Published on: January 16, 2016

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Coulomb Explosion Imaging as a Tool to Distinguish Between Stereoisomers
08:51

Coulomb Explosion Imaging as a Tool to Distinguish Between Stereoisomers

Published on: August 18, 2017

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Real-time Monitoring of Reactions Performed Using Continuous-flow Processing: The Preparation of 3-Acetylcoumarin as an Example
09:56

Real-time Monitoring of Reactions Performed Using Continuous-flow Processing: The Preparation of 3-Acetylcoumarin as an Example

Published on: November 18, 2015

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结论:

  • 立体中心编辑提供了对分子立体化学的精确,后期控制.
  • 这些方法可以从根本上改变立体定义合成的逻辑.
  • 开发的工具为访问复杂的性分子提供了巨大的潜力.