Experimental observation of structures with subtle balance between strong hydrogen bond and weak n â π(*) interaction: Gas phase laser spectroscopy of 7-azaindoleâ¯fluorosubstituted pyridines.
J Chem Phys
; 145(10): 104302, 2016 Sep 14.
Article
em En
| MEDLINE
| ID: mdl-27634255
ABSTRACT
In this study, interplay between a strong hydrogen bond and a very weak n â π(*) interaction has been probed through experiment for the first time. We have used resonant 2-photon ionization, Infrared-ultraviolet double resonance spectroscopy, and quantum chemistry calculation to determine the structures of 7-azaindoleâ¯2,6-difluoropyridine and 7-azaindoleâ¯2,3,5,6-tetrafluororpyridine complexes, which are stabilized by both hydrogen bonding and n â π(*) interaction. The structures of the complexes studied in the present work have been compared with the double hydrogen bonded (N-Hâ¯N and C-Hâ¯N) planar structure of 7-azaindoleâ¯2-fluoropyridine. It has been found that the strength of the N-Hâ¯N hydrogen bond in the 7-azaindoleâ¯2,6-substituted fluoropyridines is affected due to several factors. The main reason for huge reduction in the strength of this N-Hâ¯N hydrogen bond in these complexes is due to loss of the C-Hâ¯N hydrogen bond, through substitution of fluorine atoms in 2 and 6 positions, which induces major structural changes by bending the hydrogen bond and introducing the n â π(*) interaction. Effect of fluorination as well as presence of the n â π(*) interaction in these complexes also contributes to the reduction of the strength of the N-Hâ¯N interaction. Although it is difficult to quantify the role of the n â π(*) interaction to affect the strength of the hydrogen bond, observation of the structures, where a strong hydrogen bond and a weak n â π(*) interaction co-exist, is confirmed.
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MEDLINE
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Ano de publicação:
2016
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Article