A computational study on the ring stretching modes of halogen-substituted pyridine involved in H-bonding

✍ Scribed by Li Juan Cao; An Yong Li; Li Xu; Ying Zhang

• Publisher: John Wiley and Sons
• Year: 2011
• Tongue: English
• Weight: 393 KB
• Volume: 112
• Category: Article
• ISSN: 0020-7608
• DOI: 10.1002/qua.23012

✦ Synopsis

Abstract

Density functional method B3LYP plus the AUG‐cc‐pVDZ and AUG‐cc‐pVTZ basis sets is used to investigate ring normal modes of halogen‐substituted pyridines involved in the N**···**HX H‐bonds with HX (X = F, Cl). The results demonstrated that the formation of hydrogen bond leads to an increase in the frequencies of the ring breathing mode v~1~, the N‐para‐C stretching mode v~6__a__~ and the meta‐CC stretching mode v~8__a__~, whereas there is no change in the triangle mode v~12~ for free pyridine and a smaller blue shift for substituted pyridines. There is a strong coupling between the CY stretching vibration and the triangle mode (ortho‐ and para‐substituted) or the breathing mode (meta‐substituted) in substituted pyridines, which leads to the frequency decrease in the triangle or breathing modes. The natural bond orbital analysis suggests that electrostatic interaction and charge transfer caused by the intermolecular and intramolecular hyperconjugations are the origin of the frequency blue shift in the ring stretching modes. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012