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Aromaticidad de Möbius en [12]anuleno: isomerización cis-trans a través del desplazamiento de enlaces acoplados por
Claire Castro1, William L Karney, Miguel A Valencia
1Department of Chemistry, University of San Francisco, California 94117, USA. castroc@usfca.edu
Journal of the American Chemical Society
|July 7, 2005
Resumen
Los cambios fáciles de configuración térmica en el [12]anuleno ocurren a través de un mecanismo de desplazamiento de enlaces acoplado a torsión. Este proceso implica un estado de transición altamente aromático con topología de Möbius, que difiere de los típicos mecanismos de annuleno.
Área de la Ciencia:
- Química orgánica es la química orgánica.
- Química teórica es la química teórica.
- Química computacional es la química computacional.
Sus antecedentes:
- Los anulenos son hidrocarburos cíclicos con enlaces simples y dobles alternados.
- Comprender los procesos dinámicos y los cambios conformacionales en los annulenes es crucial para predecir su reactividad y propiedades.
- Estudios anteriores a menudo asumieron mecanismos de desplazamiento de enlaces planos para anular los cambios de configuración.
Objetivo del estudio:
- Para dilucidar el mecanismo de cambio de configuración térmica fácil en el [12]annuleno.
- Para investigar la naturaleza del estado de transición involucrado en la isomerización del anuleno [12].
- Para contrastar el mecanismo propuesto con los observados en polienos acíclicos y otros annulenes.
Principales métodos:
- Cálculos de la teoría funcional de la densidad (DFT).
- Los cálculos del clúster acoplado (CC), específicamente CCSD ((T) / cc-pVDZ//BH&HLYP/6-311+G**.
- Identificación y caracterización de los estados de transición para las vías de isomerización.
Principales resultados:
- Se identificó un mecanismo de desplazamiento de enlaces acoplado a torsión para el cambio de configuración térmica en el [12]annuleno.
- El estado de transición para este proceso exhibe alta aromaticidad y topología de Möbius.
- La barrera de isomerización calculada de 18,0 kcal/mol para el tri-trans-[12]annuleno a su di-trans isómero concuerda bien con los datos experimentales.
- Se encontraron dos estados de transición de desplazamiento de enlaces de Möbius aromáticos adicionales para otros conformadores [12]annuleno.
Conclusiones:
- Los procesos dinámicos en los [4n]anulenos neutros incluyen los anulenos aromáticos de Möbius neutros.
- El mecanismo identificado desafía las suposiciones de larga data de desplazamiento de enlaces planos en annulenes.
- Este estudio proporciona evidencia del papel significativo de la aromaticidad de Möbius en la dinámica conformacional de los annulenes.
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