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Dinámica de las reacciones competitivas: transferencia endotérmica de protones y sustitución exotérmica

Jianhua Ren¹, John I Brauman

¹Department of Chemistry, Stanford University, Stanford, California 94305-5080, USA.

Journal of the American Chemical Society

|February 26, 2004

Resumen

Investigando las reacciones de iones F(-) con dimetilsulfóxido y borano-metilsulfuro, este estudio revela cómo las reacciones de sustitución y transferencia de protones dependen de la energía de los iones. La teoría RRKM modela con precisión estas dinámicas.

Área de la Ciencia:

La cinética química es la cinética química.
Química Física es la química física.

Sus antecedentes:

Las reacciones de transferencia de protones que involucran iones F ((-) son cruciales en los procesos químicos.
La comprensión de las vías de reacción competidoras, como la sustitución (S(N) 2), es esencial para predecir la dinámica química.

Objetivo del estudio:

Para investigar la dinámica de las reacciones endotérmicas de transferencia de protones de F(-) con dimetil sulfóxido y borano-metil sulfuro.
Para analizar el canal de sustitución exotérmica (S(N) 2 que compite en el canal F(-) con la reacción borano-metil sulfuro.
Para modelar las constantes de velocidad dependientes de la energía utilizando la teoría RRKM.

Principales métodos:

Utilizó la espectrometría de masa de resonancia de iones ciclotrón de la transformación de Fourier (FT-ICR) para estudiar la dinámica de las reacciones.
Constantes de velocidad dependientes de la energía medidas en función de la energía de traslación de iones F.
Empleó el modelado cinético, específicamente la teoría RRKM (Rice-Ramsperger-Kassel-Marcus), para el análisis.

Principales resultados:

Se observaron constantes de velocidad idénticas para las reacciones de transferencia de protones F(-) con dimetilsulfóxido y borano-metilsulfuro (0.17 x 10(-9) cm(3) molécula(-1) s(-1)).
Se determinó que la constante de velocidad para la reacción S(N) 2 es de 0,90 x 10(-9) cm(3) molécula(-1) s(-1) a 350 K.
Las reacciones de transferencia de protones mostraron dependencia positiva de energía, mientras que la reacción S(N) 2 exhibió dependencia negativa de energía, volviéndose menos significativa a energías más altas.
Las predicciones de la teoría RRKM se alinearon con los cambios constantes de velocidad observados bajo la energía cinética agregada.

Conclusiones:

Los cambios dinámicos en las relaciones de ramificación entre la transferencia de protones y la sustitución son impulsados por la competencia entre las constantes de velocidad microscópicas.
La cinética dependiente de la energía proporciona información sobre los mecanismos de reacción y los estados de transición.
La teoría RRKM sirve como una herramienta valiosa para modelar la dinámica de reacción compleja de iones-moléculas.

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