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Afinidad electrofílica: una medida de reactividad para la sustitución aromática
Gergana Koleva1, Boris Galabov, Judy I Wu
1Department of Chemistry, University of Sofia, Sofia 1164, Bulgaria.
Journal of the American Chemical Society
|September 26, 2009
Resumen
La afinidad electrófila (Ealpha) cuantifica la reactividad y la regioselectividad en las reacciones de sustitución aromática electrófila. Esta nueva métrica muestra una alta correlación con los datos experimentales para la cloración, la nitratación y la bencilación de los derivados del benceno.
Área de la Ciencia:
- Química orgánica es la química orgánica.
- Química Física es la química física.
Sus antecedentes:
- Las reacciones de sustitución aromática electrofílica (S(E) Ar) son fundamentales en la síntesis orgánica.
- Comprender los factores que rigen la reactividad y la regioselectividad es crucial para predecir los resultados de las reacciones.
Objetivo del estudio:
- Racionalizar la reactividad y la regioselectividad de la cloración, la nitratación y la alquilación electrófilas de los derivados del benceno.
- Introducir y validar un nuevo parámetro teórico, la Afinidad Electrófila (Ealpha), para cuantificar estos procesos.
Principales métodos:
- Comparación de los datos de la literatura para los factores de velocidad parcial (ln f) con los parámetros teóricos de reactividad.
- Evaluación teórica de la Afinidad Electrófila (Ealpha) basada en el cambio de energía durante la formación de iones de arenio.
- Análisis de correlación entre los valores de Ealpha, potencial electrostático en núcleos (EPN) y factores de velocidad parcial experimentales.
Principales resultados:
- Se observaron altos coeficientes de correlación (r > 0,97) entre Ealpha y los factores de velocidad parcial para la cloración, la nitratación y la benzilación.
- Se encontraron correlaciones satisfactorias entre los valores de EPN y los factores de velocidad parcial experimentales para la cloración y la nitratación.
- Se observó una discrepancia en las correlaciones para la benzilación, atribuida a los efectos estéricos del grupo benzil.
Conclusiones:
- La Afinidad Electrófila (Ealpha) es una medida cuantitativa útil para predecir la reactividad y la regioquímica en las reacciones S(E) Ar.
- Los valores de EPN reflejan efectivamente las variaciones de densidad de electrones relevantes para la cloración y la nitratación.
- Los factores estéricos influyen significativamente en las reacciones que involucran electrofilos voluminosos como la fracción bencílica.
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