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Influencia de los enlaces de hidrógeno inter e intramoleculares en las descarboxilaciones kemp de las simulaciones
Orlando Acevedo1, William L Jorgensen
1Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520-8107, USA.
Journal of the American Chemical Society
|June 16, 2005
Resumen
La descarboxilación Kemp de los derivados del benzisoxazol es significativamente más rápida en disolventes apróticos debido a la mala disolución de los aniones reactivos. Los enlaces internos de hidrógeno y el emparejamiento iónico pueden inhibir esta importante reacción orgánica.
Área de la Ciencia:
- Química orgánica es la química orgánica.
- Química computacional es la química computacional.
- Química Física es la química física.
Sus antecedentes:
- La descarboxilación de Kemp es una reacción clave en la síntesis orgánica.
- Comprender los efectos del disolvente y las interacciones intramoleculares es crucial para la optimización de la reacción.
Objetivo del estudio:
- Para investigar la descarboxilación de Kemp de los derivados del ácido benzisoxazol-3-carboxílico.
- Para aclarar los roles de la solvación y la unión de hidrógeno intramolecular en las velocidades de reacción.
- Para validar métodos computacionales para predecir la cinética de la reacción.
Principales métodos:
- Cálculos de Mecánica Cuántica/Mecánica Molecular (QM/MM). cálculos de Mecánica Cuántica/Mecánica Molecular (QM/MM). cálculos de Mecánica Cuántica/Mecánica Molecular. cálculos de Mecánica Cuántica/Mecánica Molecular. cálculos de Mecánica Cuántica/Mecánica Molecular. cálculos de Mecánica Cuántica/Mecánica Molecular. cálculos de Mecánica Cuántica/Mecánica Molecular. cálculos de Mecánica Cuántica/Mecánica Molecular. cálculos de Mecánica Cuántica/Mecánica Molecular.
- Simulaciones de Monte Carlo con Perturbación de Energía Libre (MC/FEP).
- Cálculo de los potenciales bidimensionales de la fuerza media (PMF).
Principales resultados:
- Los disolventes apróticos aceleran la reacción en 7-8 órdenes de magnitud en comparación con el agua.
- Los enlaces internos de hidrógeno inhiben significativamente la reacción, independientemente del disolvente.
- La menor disolución del anión reactivo en disolventes aproticos dipolares impulsa el aumento de la velocidad.
- El emparejamiento iónico en cloroformo explica la velocidad experimental anormalmente lenta.
Conclusiones:
- Las simulaciones QM/MM/MC predicen con precisión las energías libres de activación experimental.
- La disolución y el enlace de hidrógeno intramolecular son factores críticos que controlan las tasas de descarboxilación de Kemp.
- El método PDDG / PM3 QM dentro del marco QM / MM / MC es un enfoque confiable para estudiar tales reacciones.
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