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Videos de Conceptos Relacionados

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.
Valence Bond Theory02:42

Valence Bond Theory

Coordination compounds and complexes exhibit different colors, geometries, and magnetic behavior, depending on the metal atom/ion and ligands from which they are composed. In an attempt to explain the bonding and structure of coordination complexes, Linus Pauling proposed the valence bond theory, or VBT, using the concepts of hybridization and the overlapping of the atomic orbitals. According to VBT, the central metal atom or ion (Lewis acid) hybridizes to provide empty orbitals of suitable...
Valence Bond Theory02:45

Valence Bond Theory

Overview of Valence Bond Theory
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...
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...
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

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Line Shape Analysis of Dynamic NMR Spectra for Characterizing Coordination Sphere Rearrangements at a Chiral Rhenium Polyhydride Complex
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La interconversión dinámica centrada en Ti (IV) entre las moléculas de anillo y de jaula que contienen Pd (II), Ti

Shuichi Hiraoka1, Yoko Sakata, Mitsuhiko Shionoya

  • 1Department of Chemistry, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. hiraoka@chem.s.u-tokyo.ac.jp

Journal of the American Chemical Society
|July 11, 2008
PubMed
Resumen

Los investigadores crearon nuevos complejos supramoleculares utilizando un ligando piridil catecol, titanio y paladio. Estos complejos son interconvertibles, mostrando cambios dinámicos de coordinación centrados en Ti4+ impulsados por la fracción de componentes y la basicidad.

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Área de la Ciencia:

  • Coordinación Química de la Coordinación
  • Química supramolecular de las moléculas.
  • Ciencia de los materiales Ciencia de los materiales.

Sus antecedentes:

  • La química supramolecular se centra en las interacciones no covalentes para construir estructuras complejas.
  • Los complejos heteronucleares ofrecen propiedades únicas debido a la presencia de múltiples centros metálicos.
  • Los complejos de titanio y paladio son ampliamente estudiados por sus aplicaciones catalíticas y estructurales.

Objetivo del estudio:

  • Para construir nuevos complejos heteronucleares, de anillo supramolecular y de jaula.
  • Investigar la interconvertibilidad entre las diferentes estructuras de coordinación centradas en Ti4+.
  • Comprender los factores que influyen en las transformaciones estructurales centradas en Ti4+.

Principales métodos:

  • Síntesis de complejos heteronucleares utilizando un ligando de catecol pirídico, TiO ((acac) 2) y PdCl2 ((CH3CN) 2.
  • Análisis espectroscópicos y cristalográficos para caracterizar los complejos.
  • Investigación de las condiciones de reacción, incluida la fracción de componentes y la basicidad, para estudiar la interconversión.

Principales resultados:

  • Construyó con éxito complejos heteronucleares, de anillo supramolecular y de jaula.
  • Se ha demostrado la interconversión cuantitativa entre dos estructuras de coordinación distintas centradas en Ti4+: Ti (catecolato) 3 y TiH (catecolato) 2 (acetilacetonato).
  • Identificó la fracción de componentes y la basicidad como factores clave que impulsan los cambios estructurales centrados en Ti4+.

Conclusiones:

  • El estudio presenta nuevos complejos supramoleculares heteronucleares con coordinación dinámica Ti4 + centrada.
  • El mecanismo de interconversión proporciona información sobre la flexibilidad y capacidad de respuesta de estos complejos.
  • Los hallazgos contribuyen a la comprensión del autoensamblaje y la diversidad estructural en la química de coordinación.