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Bond Dissociation Energy and Activation Energy02:13

Bond Dissociation Energy and Activation Energy

Bond energy is the energy required to break a bond homolytically. These values are usually expressed in units of kcal/mol or kJ/mol and are referred to as bond dissociation energies when given for specific bonds or average bond energies when indicated for a given type of bond over many compounds. Firstly, the bond dissociation energy for a single bond is weaker than that of a double bond, which in turn is weaker than that of a triple bond. Secondly, hydrogen forms relatively strong bonds with...
Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

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

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

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...
Radical Formation: Homolysis00:54

Radical Formation: Homolysis

A bond is formed between two atoms by sharing two electrons. When this bond is broken by supplying sufficient energy, either two electrons can be taken up by one atom forming ions by the cleavage called heterolysis, or the two electrons are shared by two atoms, with one each creating radicals by the cleavage called homolysis.
Cycloaddition Reactions: MO Requirements for Thermal Activation01:16

Cycloaddition Reactions: MO Requirements for Thermal Activation

Thermal cycloadditions are reactions where the source of activation energy needed to initiate the reaction is provided in the form of heat. A typical example of a thermally-allowed cycloaddition is the Diels–Alder reaction, which is a [4 + 2] cycloaddition. In contrast, a [2 + 2] cycloaddition is thermally forbidden.
Cycloaddition Reactions: MO Requirements for Photochemical Activation01:12

Cycloaddition Reactions: MO Requirements for Photochemical Activation

Some cycloaddition reactions are activated by heat, while others are initiated by light. For example, a [2 + 2] cycloaddition between two ethylene molecules occurs only in the presence of light. It is photochemically allowed but thermally forbidden.

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Updated: Jul 13, 2026

Synthesis of Antiviral Tetrahydrocarbazole Derivatives by Photochemical and Acid-catalyzed C-H Functionalization via Intermediate Peroxides (CHIPS)
06:34

Synthesis of Antiviral Tetrahydrocarbazole Derivatives by Photochemical and Acid-catalyzed C-H Functionalization via Intermediate Peroxides (CHIPS)

Published on: June 20, 2014

Comprender y explotar la activación de los bonos C-H.

Jay A Labinger1, John E Bercaw

  • 1Arnold and Mabel Beckman Laboratories of Chemical Synthesis, California Institute of Technology, Pasadena, California 91125, USA. jal@its.caltech.edu

Nature
|May 31, 2002
PubMed
Resumen

Los científicos están avanzando en la transformación selectiva de enlaces carbono-hidrógeno (C-H) utilizando metales de transición. Esta investigación promete una síntesis química más eficiente y una utilización más limpia de los abundantes recursos de alcano.

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Área de la Ciencia:

  • Química organometálica Química orgánica de los metales.
  • La catálisis es la catálisis.
  • Química Sostenible y Sustentable

Sus antecedentes:

  • Los enlaces carbono-hidrógeno (C-H) son abundantes pero inertes, lo que presenta un desafío para la síntesis química.
  • La catálisis de metales de transición ha surgido como una poderosa herramienta para la activación de enlaces C-H.
  • Se han logrado avances significativos en la comprensión de los mecanismos de activación de C-H en las últimas dos décadas.

Objetivo del estudio:

  • Revisar los avances en la activación de enlaces C-H catalizados por metales de transición.
  • Discutir el potencial de estos métodos para aplicaciones prácticas en la síntesis química y la conversión de alcano.
  • Para resaltar el desarrollo en curso de sistemas catalíticos para la utilización eficiente y limpia de los recursos de alcano.

Principales métodos:

  • Revisión de la literatura sobre la activación de enlaces C-H catalizados por metales de transición.
  • Análisis de los mecanismos de reacción, la selectividad y las condiciones.
  • Evaluación de las aplicaciones actuales y potenciales en la síntesis química fina y la sustitución de materias primas.

Principales resultados:

  • Se han reportado numerosos ejemplos de activación selectiva de enlaces C-H en centros de metales de transición bajo condiciones suaves.
  • Se ha logrado una comprensión más profunda de los mecanismos, ventajas y limitaciones de estas reacciones organometálicas.
  • Nuevos y prometedores sistemas catalíticos demuestran la viabilidad de estrategias prácticas de activación de C-H.

Conclusiones:

  • La química organometálica ofrece un potencial significativo para la activación eficiente y selectiva de enlaces C-H.
  • Un mayor desarrollo de los sistemas catalíticos es crucial para la realización de aplicaciones prácticas en la conversión de alcano.
  • Estos avances allanan el camino para una utilización más limpia y eficiente de los recursos de alcano de la Tierra.