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Equilibrios ceto-enol/enolatos en el sistema N-acetilamino-p-metilacetofenona. Efecto de un sustituto de
Y Chiang1, A G Griesbeck, H Heckroth
1Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada.
Journal of the American Chemical Society
|September 13, 2001
Resumen
El sustituto de N-acetilamino aumenta significativamente el equilibrio ceto-enol y las constantes de acidez de N-acetilamino-p-metilacetofenona. Este sustituto también ralentiza drásticamente la tasa de cetonización del enol catalizado por ácido.
Área de la Ciencia:
- Química orgánica es la química orgánica.
- Física Química orgánica Física Química orgánica
- La cinética de la reacción.
Sus antecedentes:
- Comprender los efectos electrónicos de los sustituyentes en la enolización de cetonas es crucial en la química orgánica.
- La influencia del grupo N-acetilamino en la acidez y el equilibrio del tautomerismo cetona-enol requiere una investigación detallada.
Objetivo del estudio:
- Para cuantificar el impacto del sustituto N-acetylamino en el equilibrio ceto-enol y la acidez de la p-metilacetofenona.
- Determinar las tasas de enolización y cetonización de la N-acetilamina-p-metilacetofenona bajo diversas condiciones.
Principales métodos:
- La fotólisis de flash se utilizó para generar el intermediario cis-enol.
- Las tasas de cetonización se midieron en soluciones ácidas y básicas, así como en varios sistemas de amortiguación.
- Las tasas de enolización se determinaron mediante el intercambio de hidrógeno de protones de metileno.
Principales resultados:
- Se encontró que la constante de equilibrio ceto-enol (K(E)) era 5.33.
- Las constantes de acidez para las formas de enol (Q(a) (E)) y cetona (Q(a) (K)) se determinaron como 9.12 y 14.45, respectivamente.
- El sustituto N-acetylamino aumentó K (E) en 3 órdenes de magnitud, Q (a) (E) en 1 orden, y Q (a) (K) en 4 órdenes, mientras que retardaba la cetonización catalizada por H+ en 4 órdenes.
Conclusiones:
- El grupo N-acetilamino estabiliza significativamente la forma enol y altera la acidez de los tautómeros enol y cetona.
- Los efectos de sustitución observados se atribuyen a las influencias electrónicas en el equilibrio y las vías de reacción.
- Este estudio proporciona datos cuantitativos sobre el impacto de los sustitutos donantes de electrones en la química de las cetonas.
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