Origin of Substituent Effect on Tautomeric Behavior of 1,2,4-Triazole Derivatives: Combined Spectroscopic and Theoretical Study

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• 作者：Tetiana Sergeieva ; Maria Bilichenko ; Sergiy Holodnyak ; Yulia V. Monaykina ; Sergiy I. OkovytyySergiy I. Kovalenko ; Eugene Voronkov ; Jerzy Leszczynski
• 刊名：Journal of Physical Chemistry A
• 出版年：2016
• 出版时间：December 29, 2016
• 年：2016
• 卷：120
• 期：51
• 页码：10116-10122
• 全文大小：564K
• ISSN：1520-5215

文摘

The reaction of 2-aryl-[1,2,4]triazolo[1,5-c]quinazolines with nucleophilic reagents (hydrazine hydrate, sodium hydroxide, sodium methoxide, hydrochloric acid) under acidic conditions leads to formation of compounds that tend to tautomerize. The products of the transformation are distinguished by the position (ortho-, meta-, para-) of the OCH₃ group in the aryl moiety. To assign their structures we used the combined approach: experiment and theoretical modeling. The procedure included calculation of the relative stability for possible tautomers, simulation of UV/vis spectra for the most stable forms, and comparison of the resulting curves with the experimental spectral data taking into account the Boltzmann weighting. Through computations, we showed that the orientation of OCH₃ substituent remarkably impacts on the tautomeric behavior of triazoles. In the case of ortho-OCH₃ it is controlled by formation of the intramolecular hydrogen bond while for meta- and para- derivatives the degree of conjugation plays the decisive role. In order to balance the accuracy and cost of calculations we evaluated the performance of selected DFT methods and 6-31G*, 6-311++G**, and STO^##-3G_el basis sets. The last one is a physically justified basis set previously constructed in our group, and its combination with PBE1PBE approach is shown to be the best choice for UV/vis simulations in the frame of the current research.