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Videos de Conceptos Relacionados

Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)01:22

Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)

Vicinal or three-bond coupling is commonly observed between protons attached to adjacent carbons. Here, nuclear spin information is primarily transferred via electron spin interactions between adjacent C‑H bond orbitals. This generally favors the antiparallel arrangement of spins, so 3J values are usually positive.
The extent of coupling depends on the C‑C bond length, the two H‑C‑C angles, any electron-withdrawing substituents, and the dihedral angle between the involved orbitals. The...
Woodward–Hoffmann Selection Rules and Microscopic Reversibility01:34

Woodward–Hoffmann Selection Rules and Microscopic Reversibility

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...
Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)

Two NMR-active nuclei bonded to a central atom can be involved in geminal or two-bond coupling. Geminal coupling is commonly seen between diastereotopic protons in chiral molecules and unsymmetrical alkenes, among others.
The central atom need not be NMR-active because its electrons are affected by the electron polarization of the spin-active atoms. However, spin information is transmitted less effectively than in one-bond coupling, and 2J values are usually weaker than 1J values. The energy of...
Aromatic Hydrocarbon Cations: Structural Overview01:18

Aromatic Hydrocarbon Cations: Structural Overview

Cycloheptatriene is a neutral monocyclic unsaturated hydrocarbon that consists of an odd number of carbon atoms and an intervening sp3 carbon in the ring. The three double bonds in the ring correspond to 6 π electrons, which is a Huckel number, and therefore satisfies the criteria of 4n + 2 π electrons. However, the intervening sp3 carbon disrupts the continuous overlap of p orbitals. As a result, cycloheptatriene is not aromatic.
Removing one hydrogen from the intervening CH2 group with both...
Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal Electrocyclic Reactions: Stereochemistry

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.

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Amide Coupling Reaction for the Synthesis of Bispyridine-based Ligands and Their Complexation to Platinum as Dinuclear Anticancer Agents
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Acoplamiento C-C reversible en un complejo biheterocíclico de uranio.

Marisa J Monreal1, Paula L Diaconescu

  • 1Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, USA.

Journal of the American Chemical Society
|April 6, 2010
PubMed
Resumen

Los científicos lograron el acoplamiento C-C de 1-metilbenzimidazol utilizando un complejo de uranio. Esta reacción implica la activación de C-H y forma un producto biheterocíclico reversible, confirmado por difracción de rayos X y RMN.

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Área de la Ciencia:

  • Química organometálica Química orgánica de los metales.
  • Química del Uranio La Química del Uranio
  • Química Heterocíclica La Química Heterocíclica es una de las más conocidas.

Sus antecedentes:

  • Las reacciones de acoplamiento C-C son fundamentales en la síntesis orgánica.
  • Los complejos de uranio ofrecen una reactividad única para transformaciones desafiantes.
  • El 1-metilbenzimidazol es un andamio heterocíclico relevante.

Objetivo del estudio:

  • Para investigar el acoplamiento C-C del 1-metilbenzimidazol mediado por un complejo uranio-dibenzil.
  • Para dilucidar el mecanismo que involucra la activación C-H y el acoplamiento de fragmentos.
  • Para caracterizar el producto biheterocíclico resultante y evaluar la reversibilidad de la reacción.

Principales métodos:

  • Síntesis de un complejo neutro de uranio dibencilo con un ligando ferroceno 1,1'-diamida.
  • Difracción de rayos X (cristal único y polvo) para la determinación de la estructura en estado sólido.
  • Espectroscopia de RMN de temperatura variable ((1) H y (2) H) y cálculos de DFT para estudios de soluciones y conocimientos mecanicistas.

Principales resultados:

  • Se logró el acoplamiento exitoso C-C de dos moléculas de 1-metilbenzimidazol.
  • La reacción procede a través de la activación de C-H y la formación de una fracción biheterocíclica.
  • La estructura en estado sólido confirmó la formación del producto; los estudios de solución revelaron que el acoplamiento es reversible.

Conclusiones:

  • Se ha demostrado un nuevo acoplamiento C-C de 1-metilbenzimidazol utilizando un complejo de uranio.
  • El estudio proporciona información sobre el mecanismo de activación y acoplamiento de C-H mediado por uranio.
  • La naturaleza reversible de la reacción abre caminos para nuevas aplicaciones sintéticas.