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Videos de Conceptos Relacionados

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

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

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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...
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ortho–para-Directing Deactivators: Halogens01:24

ortho–para-Directing Deactivators: Halogens

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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...
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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...
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Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal Electrocyclic Reactions: Stereochemistry

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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...
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Protocol for the Synthesis of Ortho-trifluoromethoxylated Aniline Derivatives
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Activación selectiva ortho-CH en arenas sin grupos funcionales

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
Resumen
Este resumen es generado por máquina.

Los investigadores desarrollaron un nuevo método para la activación altamente selectiva de orto-C-H en alquilarenos utilizando complejos de iridio. Este avance ofrece una nueva ruta para sintetizar moléculas orgánicas funcionales a partir de hidrocarburos simples.

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Área de la Ciencia:

  • Química orgánica
  • Catálisis
  • Metodología sintética

Sus antecedentes:

  • La activación aromática de C-H es crucial para la síntesis de moléculas orgánicas funcionales.
  • Los métodos existentes a menudo dan lugar a mezclas debido a la activación preferente de enlaces C-H menos obstaculizados.

Objetivo del estudio:

  • Para lograr una activación orto-C-H altamente selectiva en los alquileranos.
  • Desarrollar un nuevo sistema catalítico para la funcionalización del C-H aromático.

Principales métodos:

  • Se utilizan complejos de iridio simples para la activación catalítica de C-H.
  • Investigó el mecanismo que implica la inserción transitoria en el enlace bencílico C-H.

Principales resultados:

  • Se ha demostrado una activación orto-C-H altamente selectiva en los alquileranos.
  • Se demostró que los sustituyentes alquilo más voluminosos mejoran la orto selectividad.
  • Identificó un mecanismo que involucra la inserción y regeneración de enlaces bencílicos C-H.

Conclusiones:

  • Desarrolló un enfoque conceptualmente nuevo para la activación de enlaces aromáticos C-H.
  • El método proporciona una alternativa selectiva a las estrategias de activación de C-H existentes.
  • Ofrece un control preciso sobre la funcionalidad de los compuestos aromáticos.