An ab Initio Study of the Effect of Substituents on the n → π* Interactions between 7-Azaindole and 2,6-Difluorosubstituted Pyridines

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• 作者：Santosh K. Singh ; Aloke Das ; Gary W. Breton
• 刊名：Journal of Physical Chemistry A
• 出版年：2016
• 出版时间：August 11, 2016
• 年：2016
• 卷：120
• 期：31
• 页码：6258-6269
• 全文大小：685K
• 年卷期：0
• ISSN：1520-5215

文摘

The n → π* interaction is a weak but important noncovalent interaction present in biomolecules and other compounds. Complexes between 7-azaindole and 2,6-difluorinated pyridines were demonstrated earlier to interact not only via an expected strong hydrogen bond but also by a weaker and unexpected n → π* interaction between the nucleophilic nitrogen atom of the 7-azaindole and the electrophilic π-system of the pyridine ring. This system provides a unique and convenient framework upon which to investigate the effect that distal substitution on the 7-azaindole ring has on the strength of the n → π* interaction. Herein we describe our thorough analysis of these effects by applying a variety of diverse methods including NBO, ETS-NOCV, and AIM. Very good agreement in trends was observed among all these diverse methods of analysis. Substitution at the position para to the nucleophilic nitrogen atom of the 7-azaindole ring with electron-donating groups weakened the hydrogen bond interaction with the 2,6-difluoropyridine but enhanced the n → π* interaction. Substitution with electron-withdrawing groups had the opposite effect. In addition, good correlation of the results of the calculations with the substituents’ Hammett σ_p values was observed. Energy decomposition analysis (EDA) corroborated the conclusions derived by the other methods of analysis.