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Cinética de las reacciones de heterólisis radical que forman cationes de radicales alqueno
John H Horner1, Laurent Bagnol, Martin Newcomb
1Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, IL 60607, USA.
Journal of the American Chemical Society
|November 13, 2004
Resumen
Este estudio cuantifica las tasas de fragmentación heterolítica para los radicales alquilo beta-ésteres utilizando fotólisis de flash láser. Un grupo ciclopropilo acelera significativamente estas reacciones de heterólisis radical, lo que permite el modelado predictivo basado en la polaridad del disolvente.
Área de la Ciencia:
- Química orgánica es la química orgánica.
- Química Física es la química física.
Sus antecedentes:
- Los radicales alquilo son intermediarios clave en las reacciones orgánicas.
- Comprender sus vías de fragmentación es crucial para elucidar el mecanismo de reacción.
- Los radicales alquilo sustituidos por el éster beta presentan una dinámica de fragmentación única.
Objetivo del estudio:
- Para determinar las constantes de velocidad para la fragmentación heterolítica de los radicales beta-alquilo.
- Investigar la influencia de diferentes grupos de ésteres y modificaciones estructurales en las tasas de fragmentación.
- Desarrollar un modelo predictivo para la heterólisis radical basado en la polaridad del solvente.
Principales métodos:
- Estudios de fotólisis de flash láser directo.
- Estudios cinéticos indirectos. estudios cinéticos indirectos.
- Análisis cinético utilizando las funciones de Arrhenius.
- Mediciones de la polaridad del disolvente utilizando la escala E(T) ((30).
Principales resultados:
- Las constantes de velocidad para la fragmentación heterolítica de radicales alquilo beta-ésteres específicos (por ejemplo, 4a, 4b, 5a, 5b) se determinaron en varios disolventes.
- El radical 1,1-dimethyl-2-mesyloxyhexyl (4a) se fragmenta rápidamente (k ((het) > 5 x 10 ((9) s ((-1)).
- Un grupo de ciclopropilo reportero acelera significativamente las tasas de heterólisis (35 veces para 5a frente a 4b).
- Se generó una escala predictiva para las reacciones de heterólisis en función de la polaridad del disolvente.
Conclusiones:
- La fragmentación heterolítica de los radicales alquilo beta-ésteres es un proceso fácil.
- Las modificaciones estructurales, como la introducción de un grupo ciclopropilo, pueden influir dramáticamente en las tasas de fragmentación.
- La escala predictiva desarrollada proporciona información valiosa sobre el comportamiento dependiente del disolvente de estas reacciones radicales.
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