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Sobre el origen físico de los enlaces de hidrógeno desplazados al azul
Xiaosong Li1, Lei Liu, H Bernhard Schlegel
1Contribution from the Department of Chemistry, Wayne State University, Detroit, Michigan 48202, USA.
Journal of the American Chemical Society
|August 9, 2002
Resumen
El enlace de hidrógeno puede aumentar sorprendentemente la frecuencia de estiramiento del enlace de hidrógeno en sistemas con desplazamiento azul. Este fenómeno, observado en estudios computacionales, es impulsado principalmente por interacciones electrostáticas, no por correlación de electrones.
Área de la Ciencia:
- Química computacional es la química computacional.
- Interacciones moleculares Las interacciones moleculares.
- La espectroscopia es una técnica de espectroscopia.
Sus antecedentes:
- Los enlaces de hidrógeno generalmente implican una disminución en la frecuencia de estiramiento X-H tras la complicación.
- Los sistemas de enlace de hidrógeno con desplazamiento azul exhiben un aumento anómalo en la frecuencia de estiramiento X-H.
Objetivo del estudio:
- Investigar los mecanismos subyacentes responsables del fenómeno de desplazamiento azul en los sistemas enlazados por hidrógeno.
- Determinar el papel de las interacciones electrostáticas frente a las interacciones orbitales en la causa del desplazamiento azul.
Principales métodos:
- Los cálculos químicos cuánticos se realizaron en varios niveles de la teoría.
- Se estudió el sistema arquetípico F(3)C·H··FH y las moléculas relacionadas.
- Se realizó un análisis de la redistribución de la carga y las fuerzas intermoleculares.
Principales resultados:
- El desplazamiento azul se reprodujo a nivel de Hartree-Fock, lo que sugiere que la correlación de electrones no es la causa principal.
- Se observaron desplazamientos azules sustanciales en sistemas sin centros de carbono o pares aislados en el donante de protones.
- Se descubrió que las interacciones orbitales alargan el enlace X-H, lo que contradice la observación del desplazamiento azul.
Conclusiones:
- El desplazamiento azul en la unión de hidrógeno se rige predominantemente por las interacciones electrostáticas.
- La repulsión de Pauli entre fragmentos moleculares en geometría de equilibrio comprime el enlace X-H, causando el desplazamiento azul.
- Esta interacción repulsiva anula los efectos orbitales de alargamiento de enlaces en estos sistemas específicos.
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