Geometrical Features of Hydrogen Bonded Complexes Involving Sterically Hindered Pyridines

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• 作者：Daria V. Andreeva ; Brenda Ip ; Andrey A. Gurinov ; Peter M. Tolstoy ; Gleb S. Denisov ; Ilja G. Shenderovich ; Hans-Heinrich Limbach
• 刊名：Journal of Physical Chemistry A
• 出版年：2006
• 出版时间：September 21, 2006
• 年：2006
• 卷：110
• 期：37
• 页码：10872 - 10879
• 全文大小：144K
• 年卷期：v.110,no.37(September 21, 2006)
• ISSN：1520-5215

文摘

The ability of strongly sterically hindered pyridines to form hydrogen bonded complexes was inspected usinglow-temperature ¹H and ¹⁵N NMR spectroscopy in a liquefied Freon mixture. The proton acceptors were2,6-di(tert-butyl)-4-methyl- and 2,6-di(tert-butyl)-4-diethylaminopyridine; the proton donors were hydrogentetrafluoroborate, hydrogen chloride, and hydrogen fluoride. The presence of the tert-butyl groups in theortho positions dramatically perturbed the geometry of the forming hydrogen bonds. As revealed by experiment,the studied crowded pyridines could form hydrogen bonded complexes with proton donors exclusively throughtheir protonation. Even the strongest small proton acceptor, anion F^-, could not be received by the protonatedbase. Instead, the simplest hydrogen bonded complex involved the [FHF]^- anion. This complex wascharacterized by the shortest possible N···F distance of about 2.8 Å. Because the ortho tert-butyl groups didnot prevent the hydrogen bond interaction between the protonated center and the anion completely, an increaseof the pyridine basicity caused a further shortening of the N-H distance and a weakening of the hydrogenbond to the counterion.