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相关概念视频

ortho–para-Directing Activators: –CH3, –OH, –⁠NH2, –OCH301:11

ortho–para-Directing Activators: –CH3, –OH, –⁠NH2, –OCH3

6.3K
All ortho–para directors, excluding halogens, are activating groups. These groups donate electrons to the ring, making the ring carbons electron-rich. Consequently, the reactivity of the aromatic ring towards electrophilic substitution increases. For instance, the nitration of anisole is about 10,000 times faster than the nitration of benzene. The electron-donating effect of the methoxy group in anisole activates the ortho and para positions on the ring and stabilizes the corresponding...
6.3K
ortho–para-Directing Deactivators: Halogens01:24

ortho–para-Directing Deactivators: Halogens

5.7K
Halogens are ortho–para directors. They are more electronegative than carbon. Therefore, as ring substituents, they can withdraw electrons through the inductive effect and deactivate the aromatic ring towards electrophilic substitution. Halogens also have an electron-donating resonance effect on the ring, which influences the orientation of the incoming electrophile. If an electrophile attacks at the ortho or the para position, the halogen donates electrons and stabilizes the intermediate...
5.7K
Regioselectivity and Stereochemistry of Hydroboration02:36

Regioselectivity and Stereochemistry of Hydroboration

8.4K
A significant aspect of hydroboration–oxidation is the regio- and stereochemical outcome of the reaction.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn...
8.4K
Aromatic Hydrocarbon Anions: Structural Overview01:18

Aromatic Hydrocarbon Anions: Structural Overview

2.9K
Neutral hydrocarbons like cyclopentadiene with an odd number of carbon atoms and one intervening CH2 group in the ring are not aromatic. Cyclopentadiene with 4 π electrons does not satisfy the 4n + 2 π electron rule. Additionally, the intervening CH2 group is sp3 hybridized and lacks a vacant p orbital, thereby interrupting the overlap of p orbitals in a continuous manner and preventing the delocalization of π electrons throughout the ring.
Due to the absence of continuous...
2.9K
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
Regioselectivity of Electrophilic Additions to Alkenes: Markovnikov's Rule02:17

Regioselectivity of Electrophilic Additions to Alkenes: Markovnikov's Rule

14.7K
If a set of reactants can yield multiple constitutional isomers, but one of the isomers is obtained as the major product, the reaction is said to be regioselective. In such reactions, bond formation or breaking is favored at one reaction site over others.
The hydrohalogenation of an unsymmetrical alkene can yield two haloalkane products, depending on which vinylic carbon takes up the halogen. However, one product usually predominates, where hydrogen adds to the vinylic carbon bearing the...
14.7K

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Protocol for the Synthesis of Ortho-trifluoromethoxylated Aniline Derivatives
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在没有功能组的区域中选择性C-H激活.

Antony P Y Chan1, Martin Jakoobi1, Chenxu Wang1

  • 1Department of Chemistry, University of Liverpool, Crown Street, Liverpool L69 7ZD, U.K.

Journal of the American Chemical Society
|June 21, 2022
PubMed
概括

研究人员开发了一种新方法,用于使用复合体在基中进行高度选择性的正正C-H激活. 这一突破为从简单的碳化合物中合成功能化有机分子提供了一条新的途径.

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科学领域:

  • 有机化学 有机化学
  • 催化剂是一种催化剂.
  • 合成方法论 合成方法论

背景情况:

  • 芳香C-H激活对于合成功能化的有机分子至关重要.
  • 现有的方法往往会导致混合,原因是受阻较小的C-H债券的优先激活.

研究的目的:

  • 为了在基中实现高度选择性的正正C-H激活.
  • 开发一种用于向芳香C-H功能化的新型催化系统.

主要方法:

  • 使用简单的复合物进行催化C-H激活.
  • 研究了涉及暂时插入基C-H键的机制.

主要成果:

  • 在alkylarenes中表现出高度选择性的ortho-C-H激活.
  • 显示较大的基替代剂增强了整形选择性.
  • 确定了一种涉及基C-H键插入和再生的机制.

结论:

  • 开发了一种概念上的新方法来激活芳香C-H键.
  • 该方法为现有的C-H激活策略提供了选择性的替代方案.
  • 提供精确控制芳香化合物的功能化.