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Efectos vibratorios del punto cero en los blindajes de protones: contribuciones de grupos funcionales de cálculos ab

K Ruud¹, P O Astrand, P R Taylor

¹San Diego Supercomputer Center and Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive MC0505, La Jolla, California 92093-0505, USA.

Journal of the American Chemical Society

|July 18, 2001

Resumen

El movimiento vibratorio del punto cero impacta significativamente las constantes de blindaje magnético nuclear en las moléculas orgánicas. Estas correcciones vibratorias son cruciales para los cálculos precisos de desplazamiento químico y son transferibles para los átomos de hidrógeno.

Área de la Ciencia:

Química computacional es la química computacional.
Química cuántica es la química cuántica.
Espectroscopia molecular Espectroscopia molecular es la espectroscopia molecular.

Sus antecedentes:

Las constantes de blindaje magnético nuclear son esenciales para interpretar los espectros de RMN.
El movimiento vibratorio puede influir en las propiedades electrónicas, incluido el blindaje magnético.
Los estudios previos a menudo descuidaban o aproximaban los efectos vibratorios.

Objetivo del estudio:

Para investigar el impacto del movimiento vibratorio del punto cero en las constantes de blindaje magnético nuclear en moléculas orgánicas.
Para cuantificar las correcciones vibratorias, incluidas las contribuciones anharmónicas y armónicas.
Para evaluar la transferibilidad de estas correcciones a través de diferentes moléculas.

Principales métodos:

Ab initio cálculos de las superficies de energía potencial y las superficies de propiedades.
Inclusión de las contribuciones anharmónicas de la superficie de energía potencial.
Inclusión de las contribuciones armónicas de la curvatura de la superficie de la propiedad.
Estudio sistemático de un gran conjunto de moléculas orgánicas.

Principales resultados:

Las correcciones vibratorias a las constantes de blindaje de hidrógeno pueden ser sustanciales (+0.50 a -0.70 ppm).
Ignorar estos efectos puede conducir a errores de desplazamiento químico superiores a 1 ppm.
Las correcciones vibratorias para los blindajes de hidrógeno demuestran una significativa transferibilidad entre moléculas.
No se observó una transferencia similar para las constantes de blindaje de carbono, nitrógeno u oxígeno.

Conclusiones:

Los efectos del movimiento vibratorio de punto cero son críticos y no pueden ser descuidados para las predicciones precisas de desplazamiento químico de RMN.
Se pueden tabular y utilizar correcciones vibratorias transferibles para blindajes de hidrógeno.
Se necesita más investigación para comprender los efectos vibratorios en otros núcleos.

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