Video Experimental Relacionado
Updated: Jun 11, 2026
13:09
Utilization of Stop-flow Micro-tubing Reactors for the Development of Organic Transformations
Published on: January 4, 2018
Estudios computacionales de la cicloisomerización endo-selectiva catalizada por el tungsteno del 4-pentin-1-ol
Yinghong Sheng1, Djamaladdin G Musaev, K Subba Reddy
1Cherry L. Emerson Center for Scientific Computation and Department of Chemistry, Emory University, Atlanta, Georgia 30322, USA.
Journal of the American Chemical Society
|April 11, 2002
Resumen
Los catalizadores de carbonilo de tungsteno permiten la endocicloisomerización del 4-pentino-1-ol mediante la reducción de las barreras de activación. Este estudio computacional explica la endo-selectividad observada en estas reacciones.
Área de la Ciencia:
- Química orgánica es la química orgánica.
- Química computacional es la química computacional.
- La catálisis es la catálisis.
Sus antecedentes:
- Las reacciones de cicloisomerización son cruciales en la síntesis orgánica.
- Comprender los mecanismos de reacción y las funciones de catalizador es vital para optimizar los procesos químicos.
Objetivo del estudio:
- Para investigar computacionalmente las endo- y exo-cicloisomerizaciones de 4-pentyn-1-ol.
- Para aclarar el papel de los catalizadores de carbonilo de tungsteno en estas reacciones.
- Para explicar la endo-selectividad experimentalmente observada.
Principales métodos:
- Cálculos de la teoría funcional de la densidad (DFT).
- Uso de conjuntos de base de doble zeta y triple zeta.
- Comparación de las vías de reacción no catalizadas y catalizadas por tungsteno.
Principales resultados:
- Las cicloisomerizaciones no catalizadas exhiben barreras de activación muy altas (>50 kcal/mol).
- El catalizador de pentacarbonilo de tungsteno reduce significativamente la barrera que determina la velocidad para la endocicloisomerización a 26 kcal/mol.
- El catalizador estabiliza un intermediario clave del vinilideno y facilita la migración del hidruro.
- La exocicloisomerización sigue siendo una barrera alta (47 kcal / mol) incluso con el catalizador.
Conclusiones:
- Los catalizadores de carbonilo de tungsteno son esenciales para una eficiente endocicloisomerización del 4-pentino-1-ol.
- El mecanismo del catalizador implica la estabilización de los intermediarios y la facilitación de procesos en varios pasos.
- Estos hallazgos proporcionan una base teórica para la endoselectividad observada en reacciones relacionadas.
Más Videos Relacionados
Videos de Conceptos Relacionados
02:36Regioselectivity and Stereochemistry of Hydroboration
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 stereochemistry.
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 stereochemistry.
01:26Thermal 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.
01:17Thermal 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.
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.
01:26Photochemical 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
Selection Rules: Photochemical Activation
01:34Woodward–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...
![[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2Ffiles%2Fmedia%2Fscience-education%2Fscience-education-thumbs%2F12417.jpg&w=3840&q=75)
01:16[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction
The Diels–Alder reaction is an example of a thermal pericyclic reaction between a conjugated diene and an alkene or alkyne, commonly referred to as a dienophile. The reaction involves a concerted movement of six π electrons, four from the diene and two from the dienophile, forming an unsaturated six-membered ring. As a result, these reactions are classified as [4+2] cycloadditions.