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Carbomethoxychlorocarbene: espectroscopia, teoría, química y cinética de las moléculas
I Likhotvorik1, Z Zhu, E L Tae
1Department of Chemistry, The Ohio State University, 100 West 18th Avenue, Columbus, OH 43210, USA.
Journal of the American Chemical Society
|June 21, 2001
Resumen
La fotólisis de un éster metílico genera una especie de carbeno persistente. Este carbono es un carbono.
Área de la Ciencia:
- Química orgánica es la química orgánica.
- La fotoquímica es la fotoquímica.
- La espectroscopia es una técnica de espectroscopia.
Sus antecedentes:
- Los carbenos son intermediarios altamente reactivos cruciales en la síntesis orgánica.
- Comprender la estabilidad y la reactividad de los carbenos es clave para desarrollar nuevas metodologías sintéticas.
- El metil 8-cloro-3a,7a-metanoindano-8-carboxilato sirve como un precursor de un clorocarbeno específico.
Objetivo del estudio:
- Para caracterizar el carbometoxiclorocarbeno generado fotoquímicamente (6).
- Para investigar la reactividad y los parámetros cinéticos del carbeno 6 en varios disolventes.
- Determinar la energía de activación para la desaparición de carbenos y su relación con el reordenamiento de Wolff.
Principales métodos:
- Fotólisis del metil 8-cloro-3a,7a-metanoindano-8-carboxilato (5) a 254 nm y 300 nm. también se encuentra en la foto.
- Espectroscopia infrarroja (IR) y ultravioleta para la caracterización del carbeno.
- Cálculos de la teoría funcional de la densidad (DFT) (B3-LYP/6-31G).
- Fotólisis de flash láser (LFP) mediante el uso de un láser excimer XeCl (308 nm).
- Estudios cinéticos en Freón-113 y perfluorohexano para determinar el tiempo de vida del carbeno y las constantes de velocidad de reacción.
Principales resultados:
- Carbomethoxychlorocarbene (6) se generó como una especie persistente a 14 K.
- El espectro de infrarrojos indicó un estado de base individual no plano para el carbeno 6.
- La fotólisis en solución produjo indano (97% de rendimiento).
- El carbeno 6 exhibió reacciones de captura a través de la inserción de CH y la adición de doble enlace.
- La fotólisis de flash láser permitió medir el tiempo de vida del carbeno (114 ns en el Freón-113) y la velocidad de reacción con la piridina (2 x 10^9 M^-1 s^-1).
- Las energías de activación para la desaparición de carbenos se determinaron en diferentes disolventes, lo que sugiere un límite inferior para la reorganización de Wolff.
Conclusiones:
- Carbomethoxychlorocarbene (6) es una especie estable y caracterizable de carbenos.
- La reactividad del carbeno 6 es dependiente del disolvente, mostrando reacciones de inserción y adición.
- Los datos cinéticos proporcionan información sobre la estabilidad de los carbenos y las posibles vías de reordenamiento.
- El estudio establece una base para la utilización de este carbeno en aplicaciones sintéticas.
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