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Estudios estructurales y de velocidad de la formación de bencinas sustituidas
Jason C Riggs1, Antonio Ramirez, Matthew E Cremeens
1Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853-1301, USA.
Journal of the American Chemical Society
|February 26, 2008
Resumen
La elección del disolvente tiene un impacto significativo en la formación de benceno a partir de haloarillitios. Comprender estos efectos del disolvente es crucial para controlar la regioselectividad en las reacciones organometálicas.
Área de la Ciencia:
- Química orgánica es la química orgánica.
- Química organometálica Química orgánica de los metales.
Sus antecedentes:
- La formación de bencinas a partir de 2-haloarillitios es un paso sintético clave.
- Se sabe que la regioselectividad en estas eliminaciones está influenciada por las condiciones de reacción.
Objetivo del estudio:
- Investigar la regioselectividad dependiente del disolvente en la etapa de eliminación para la formación de bencinas 3-sustituidas y 3,6-disubstituidas.
- Para aclarar las vías mecanicistas que rigen la eliminación de haluros de litio.
Principales métodos:
- Espectroscopia de Resonancia Magnética Nuclear (RMN) (6Li y 13C) para el estudio de especies monoméricas en Tetrahidrofurano (THF).
- Teoría Funcional de Densidad (DFT) estudios computacionales para modelar estados de solvación y transición.
- Estudios cinéticos para determinar las velocidades y vías de reacción.
Principales resultados:
- Los 2-haloarillitios con grupos de retirada de electrones en la posición 6 existen como monómeros en el THF.
- Los cálculos de DFT sugieren que están involucrados los intermediarios de trisolvato.
- La eliminación de LiF procede a través de vías disociativas de THF, mientras que la eliminación de LiCl ocurre a través de vías no disociativas.
- La eliminación de LiCl y LiF del 2-cloro-6-fluorofenillitio muestra una distinta regioselectividad dependiente del disolvente debido a las vías de competencia.
Conclusiones:
- La regioselectividad de la formación de benceno es altamente dependiente de la naturaleza del haluro saliente (F vs. Cl) y la interacción con el disolvente.
- Los haloarillitios monoméricos en THF eliminan los haluros a través de vías dictadas por la interacción del haluro con el disolvente y el catión de litio.
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In 1865, August Kekule suggested the structure of benzene according to the structural theory of organic chemistry based on the three assertions—formula of benzene is C6H6, all the hydrogens of benzene are equivalent, and each carbon must have four bonds due to its tetravalency.
He proposed that benzene has a cyclic structure of six carbon atoms attached to one hydrogen atom each, with three alternating pi bonds.
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