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¿La aromaticidad en un producto de reacción aumenta o disminuye la barrera intrínseca? La cinética de la
Claude F Bernasconi1, Moisés Pérez-Lorenzo
1Department of Chemistry and Biochemistry, University of California-Santa Cruz, Santa Cruz, CA 95064, USA. bernasconi@chemistry.ucsc.edu
Journal of the American Chemical Society
|February 15, 2007
Resumen
La aromaticidad reduce las barreras intrínsecas a la transferencia de protones en los derivados de benzofurano y benzotiofeno. Este estudio revela la estabilización aromática del estado de transición, en contraste con los efectos de resonancia típicos.
Área de la Ciencia:
- Química física es la química física de las cosas.
- Química orgánica es la química orgánica.
Sus antecedentes:
- Las reacciones de transferencia de protones son fundamentales en la química.
- El papel de la aromaticidad en la influencia de la cinética de la reacción es complejo.
- El benzofurano-3(2H) -uno (3H-O) y el benzotiofeno-3(2H) -uno (3H-S) sirven como compuestos modelo.
Objetivo del estudio:
- Para investigar el efecto de la aromaticidad en las barreras intrínsecas de la transferencia de protones.
- Para determinar si la aromaticidad aumenta o disminuye estas barreras.
- Para dilucidar el mecanismo de estabilización aromática en los estados de transición.
Principales métodos:
- Estudio cinético de las reacciones de desprotonación en agua a 25°C.
- Uso de aminas e iones de hidróxido como bases.
- Determinación de las barreras intrínsecas a través de gráficos de Brønsted y cálculos de la ecuación de Marcus.
Principales resultados:
- Las barreras intrínsecas fueron más bajas para el derivado más aromático del benzotiofeno (3H-S) en comparación con el derivado del benzofurano (3H-O).
- Se confirmó que la aromaticidad reduce la barrera intrínseca a la transferencia de protones.
- La reducción observada en la altura de la barrera no es atribuible a otros factores electrónicos o estéricos.
Conclusiones:
- La aromaticidad reduce la barrera intrínseca para las reacciones de transferencia de protones.
- La estabilización aromática del estado de transición ocurre antes de la transferencia de protones.
- Esto contrasta con los efectos de resonancia que típicamente aumentan las barreras intrínsecas.
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