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Papel de la entropía en el aumento de las tasas de reacciones intramoleculares
Anthony A Armstrong1, L Mario Amzel
1Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, MD 21205-2185, USA.
Journal of the American Chemical Society
|November 20, 2003
Resumen
La diferencia de entropía entre el terreno accesible y los estados de transición tiene un impacto significativo en las tasas de reacción de condensación intramolecular. La entropía conformal, no vibratoria, es el motor clave de la activación de la energía libre en estas reacciones.
Área de la Ciencia:
- Química orgánica es la química orgánica.
- Química Física es la química física.
- La cinética química es la cinética química.
Sus antecedentes:
- Las reacciones de condensación intramoleculares son cruciales en la síntesis orgánica.
- Se sabe que las tasas de reacción están influenciadas por la estructura de las moléculas que reaccionan.
Objetivo del estudio:
- Para investigar los orígenes entrópicos de las variaciones de velocidad en la condensación intramolecular de monoester de ácido dicarboxílico.
- Para determinar la contribución de la entropía conformacional y vibratoria a la energía libre de activación.
Principales métodos:
- Estimación de la diferencia de entropía (DeltaS(NAC,S)) entre los conformadores del estado fundamental y los conformadores similares al estado de transición.
- Análisis de correlación entre las constantes de velocidad de reacción DeltaS ((NAC,S) estimadas y las experimentalmente determinadas.
- Análisis de modo normal para evaluar las contribuciones de entropía vibratoria.
Principales resultados:
- Se observó una fuerte correlación entre DeltaS ((NAC,S) y las tasas de reacción (R ((2) = 0,96 y 0,73).
- El análisis de modo normal indicó una contribución mínima de los cambios de entropía vibratoria.
- Se encontró que las diferencias de entropía conformacional eran significativas.
Conclusiones:
- Las diferencias de entropía conformacional entre los estados básico y de transición son un factor importante en la energía libre de activación.
- El estudio aclara los factores entrópicos que rigen la cinética de las reacciones de condensación intramolecular.
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