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Radical Reactivity: Overview01:11

Radical Reactivity: Overview

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Radicals, the highly reactive species, gain stability by undergoing three different reactions. The first reaction involves a radical-radical coupling, in which a radical combines with another radical, forming a spin‐paired molecule. The second reaction is between a radical and a spin‐paired molecule, generating a new radical and a new spin‐paired molecule. The third reaction is radical decomposition in a unimolecular reaction, forming a new radical and a spin‐paired...
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Radical Reactivity: Intramolecular vs Intermolecular01:33

Radical Reactivity: Intramolecular vs Intermolecular

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Radical reactions can occur either intermolecularly or intramolecularly. In an intermolecular radical reaction, a nucleophilic radical adds to an electrophilic alkene or vice versa. In such reactions, the radical and generally the alkene, which is also called the radical trap, are two different molecules. Additionally, for such intermolecular reactions to occur, the radical trap must be active, present in an excess concentration, and the radical starting material must have a weak...
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Radical Chain-Growth Polymerization: Chain Branching01:17

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The skeletal structure of polymers synthesized via radical polymerization is always branched. For example, the polymerization of ethylene by radical polymerization results in a low-density grade of polyethylene with a heavily branched skeletal structure. Here, the radical site abstracts hydrogen from the growing chain, and the radical site shifts from the end (a primary carbon center) to anywhere within the growing chain (a secondary carbon center). Consequently, the part of the chain from the...
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Radical Formation: Overview01:03

Radical Formation: Overview

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A bond can be broken either by heterolytic bond cleavage to form ions or homolytic bond cleavage to yield radicals. A fishhook arrow is used to represent the motion of a single electron in homolytic bond cleavage. There are two main sources from which radicals can be formed:
Radicals from spin-paired molecules:
Radicals can be obtained from spin-paired molecules either by homolysis or electron transfer. While two radicals are formed in the former, an electron is added in the...
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Radical Halogenation: Stereochemistry01:33

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Stereochemistry is the study of the different spatial arrangements of atoms in a given molecule. The stereochemistry of radical halogenations can be understood from three different situations:
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Radical Formation: Addition00:47

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Radicals can be formed by adding a radical to a spin-paired molecule. This is typically observed with unsaturated species, where the addition of a radical across the π bond leads to the production of a new radical by dissolving the π bond. For example, the addition of a Br radical to an alkene yields a carbon-centered radical.
Similar to charge conservation in chemical reactions, spin conservation is implicit for radical reactions. Accordingly, the product formed must possess an...
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Isomerización radical y cicloisomerización iniciada por la transferencia de H

Gang Li1, Jonathan L Kuo1, Arthur Han1

  • 1Department of Chemistry, Columbia University , 3000 Broadway, New York, New York 10027, United States.

Journal of the American Chemical Society
|May 12, 2016
PubMed
Resumen
Este resumen es generado por máquina.

Los catalizadores de cobalto bajo presión de hidrógeno pueden isomerizar las olefinas o formar productos ciclizados. La baja concentración de donante de cobalto H favorece la isomerización y la ciclización, a diferencia de otros catalizadores con altas concentraciones de donante.

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Área de la Ciencia:

  • Química orgánica de los metales
  • Catálisis
  • Síntesis orgánica

Sus antecedentes:

  • Los complejos de cobalto se exploran como catalizadores para diversas transformaciones orgánicas.
  • Los mecanismos de transferencia del átomo de hidrógeno (H) son cruciales en los ciclos catalíticos.
  • El control de la concentración del donante H influye en las vías de reacción.

Objetivo del estudio:

  • Investigar la actividad catalítica de los complejos de cobalto (II) bis (difluoroborilo) dimetilglioxima.
  • Aclarar el papel de la concentración donante de H en las transformaciones de las olefinas.
  • Para diferenciar entre las vías de isomerización y ciclización.

Principales métodos:

  • Reacción de Co (II) (dmgBF2) 2L2 (L = H2O, THF) con H2.
  • Estudio de la transferencia de H del complejo de cobalto a las olefinas.
  • Análisis de los productos de reacción, incluidas las olefinas isomerizadas y ciclizadas.

Principales resultados:

  • La baja concentración del donante de cobalto H• favorece la isomerización y la ciclización de la olefina.
  • Los radicales intermedios pueden transferir H• de nuevo al metal o someterse a adición intramolecular.
  • La alta concentración de H• donante con otros catalizadores favorece la hidrogenación y la ciclohidrogenación.

Conclusiones:

  • La concentración del donante de cobalto H• es un factor clave en la dirección de las vías de reacción de las olefinas.
  • Este estudio proporciona información sobre la catálisis selectiva a través del control mecanicista.
  • Los complejos de cobalto ofrecen reactividad ajustable para la funcionalización de la olefina.