Nuclear Quadrupole Resonance Investigation of Hydrogen Bonding in Some Cocrystals of 2,3,5,6-Tetramethylpyrazine and Carboxylic Acids

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• 作者：Janez Seliger ; Veselko ?agar
• 刊名：Journal of Physical Chemistry B
• 出版年：2014
• 出版时间：January 30, 2014
• 年：2014
• 卷：118
• 期：4
• 页码：996-1002
• 全文大小：267K
• ISSN：1520-5207

文摘

Cocrystals of 2,3,5,6-tetramethylpyrazine and several carboxylic acids have been prepared, and the complete ¹⁴N nuclear quadrupole resonance spectra have been measured. The ¹⁴N nuclear quadrupole resonance spectra have been used to check whether the cocrystals are indeed formed and to investigate the hydrogen bonding scheme of 2,3,5,6-tetramethylpyrazine molecules. Since a 2,3,5,6-tetramethylpyrazine molecule has two hydrogen bond acceptors, it may form either 1:1 or 1:2 cocrystals with carbocylic acids. ¹⁴N nuclear quadrupole resonance is used to distinguish between these two possibilities. Rather large ¹⁴N quadrupole coupling constants in the investigated cocrystals show that in these systems proton transfer O鈥揌路路路N 鈫?O^{鈥?/sup>路路路H鈥揘+ does not occur. The quadrupole coupling tensor in 2,3,5,6-tetramethylpyrazine cocrystals has been analyzed in terms of the deformation of the electron lone pair orbital and population of the 蟺-electron orbital. The analysis shows that the two effects are correlated.}