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Energía de deformación del anillo en el sistema ciclooctil. El efecto de la energía de deformación en [3 + 2]
1Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, USA. rbach@udel.edu
Journal of the American Chemical Society
|March 24, 2009
Resumen
Este estudio calcula las energías de tensión de anillo y las entalpías de hidrogenación para alquenos y alquinas cíclicos. Estos valores se correlacionan con las barreras de reacción de cicloadición, ofreciendo información sobre la química del anillo de tensión.
Área de la Ciencia:
- Química computacional es la química computacional.
- Química orgánica es la química orgánica.
- La cinética de la reacción.
Sus antecedentes:
- La tensión del anillo influye significativamente en la reactividad de las moléculas orgánicas cíclicas.
- Comprender las energías de deformación (SEs) y las entalpías de hidrogenación (DeltaH ((hyd)) es crucial para predecir el comportamiento químico.
- Los alquenos, alquinas y alenos cíclicos presentan propiedades estructurales y energéticas únicas debido a las restricciones de anillo.
Objetivo del estudio:
- Para calcular SEs y DeltaH ((hid) para una serie de alquenos, alquinas y alenos cíclicos (C5-C9).
- Para investigar la correlación entre SEs, DeltaH ((hyd) y las barreras de activación para las reacciones de [3+2] cicloadición.
- Para evaluar el impacto de la sustitución de flúor en la energía de deformación de la ciclooctina.
Principales métodos:
- Utilizó el nivel G3 de la teoría para cálculos computacionales de alta precisión.
- Se calcula SEs y DeltaH ((hid) para varios compuestos cíclicos.
- Parámetros energéticos correlacionados con barreras de activación calculadas para reacciones de cicloadición utilizando el nivel teórico B3LYP/6-311+G(3df,2p).
Principales resultados:
- Se han determinado las SE para la ciclopentina (48,4 kcal/mol), la ciclohexina (40,1 kcal/mol) y la cicloheptina (25,4 kcal/mol).
- Las SE calculadas para el E-ciclohexeno (49,3 kcal/mol) y el E-ciclohepteno (25,2 kcal/mol).
- Cyclooctyne exhibe un SE más alto (19.9 kcal / mol) que el E-cicloocteno (17.9 kcal / mol).
- 3,3-difluorocyclooctyne (DIFO) muestra una SE reducida (17,3 kcal / mol).
- Las barreras de activación de la cicloadición son más bajas para los alcinos y alquenos cíclicos tensados en comparación con sus contrapartes acíclicas.
- DIFO demuestra energías de activación reducidas para la cicloadición con azidas.
Conclusiones:
- SEs y DeltaH ((hyd) son descriptores valiosos para la reactividad de los sistemas cíclicos de tensión.
- La tensión del anillo tiene un impacto directo en la cinética de las reacciones de [3+2] cicloadición.
- La sustitución de flúor puede modular la tensión y la reactividad de las alquinas cíclicas.
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