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Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses
Published on: June 7, 2018
¿Puede uno predecir los cambios de los mecanismos S(N) 1 a S(N) 2?
Thanh Binh Phan1, Christoph Nolte, Shinjiro Kobayashi
1Department Chemie und Biochemie der Ludwig-Maximilians-Universität München, Butenandtstrasse 5-13 (Haus F), 81377 München, Germany.
Journal of the American Chemical Society
|July 29, 2009
Resumen
Este estudio revela que las reacciones de bromuro de benzhidril con aminas se producen a través de las vías concurrentes S(N) 1 y S(N) 2. El mecanismo S(N) 2 es favorecido sólo cuando la vida útil de los iones benxidrilo lo requiere, lo que demuestra un cambio basado en la estabilidad intermedia.
Área de la Ciencia:
- Química orgánica es la química orgánica.
- La cinética de la reacción.
- Física Química orgánica Física Química orgánica
Sus antecedentes:
- Los bromuros de benjidrilo sustituidos reaccionan con las aminas en el DMSO, produciendo aminas, benzofenonas y benjidrolos.
- El análisis cinético revela una ley de velocidad que indica vías paralelas amino-dependientes (S(N) 2) y amino-independientes (S(N) 1).
Objetivo del estudio:
- Para dilucidar los mecanismos de las reacciones entre los bromuros de benzhidril sustituidos y las aminas.
- Para investigar la interacción entre S(N) 1 y S(N) 2 procesos basados en las condiciones de reacción y tiempos de vida intermedios.
- Para cuantificar los parámetros nucleófilos y electrófilos utilizando una ecuación de tasa generalizada.
Principales métodos:
- Investigaciones cinéticas a 20°C para determinar la ley de velocidad.
- Correlación de las constantes de velocidad con las constantes de Hammett sigma (((+)) para las reacciones S (((N) 1).
- Aplicación de la ecuación log k = s (E + N) para analizar la transición S (N) 1 / S (N) 2.
- Generación de iones de benjidrilo mediante fotólisis de flash láser.
Principales resultados:
- Se observó evidencia de mecanismos de reacción simultáneos S(N) 1 y S(N) 2.
- Las tasas de S(N) 1 se correlacionaron con los efectos sustitutivos (rho = -3.22), mientras que las tasas de S(N) 2 no lo hicieron, lo que indica estados de transición distintos.
- El cambio al mecanismo S(N) 2 estaba relacionado con la vida útil del intermediario de iones de benxidrilo que alcanza el límite vibratorio.
- El DMSO fue identificado como un O-nucleófilo más fuerte que el agua y los alcoholes.
Conclusiones:
- El mecanismo de reacción pasa de S(N) 1 a S(N) 2 cuando el tiempo de vida del ion benhidrilio está limitado por la velocidad de reacción con el nucleófilo.
- El estudio proporciona un marco cuantitativo para la comprensión de las reacciones de sustitución nucleófila que involucran intermediarios de carbocatión.
- Se caracterizó la nucleofilicidad de DMSO en relación con otras O-nucleofilas.
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