Molecular and Ionic Hydrogen Bond Formation in Fluorous Solvents
Molecular and Ionic Hydrogen Bond Formation in Fluorous Solvents
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DOI：
10.1021/jp8084155
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发表时间：
2009-01-08
影响因子：
3.3
通讯作者：
Weber, Stephen G.
中科院分区：
文献类型：
--
作者：
O'Neal, Kristi L.;Weber, Stephen G.
关于氟溶剂中非共价缔合的研究很少，定量的研究就更少了。充分了解，特别是氟溶剂中非共价相互作用的化学计量学和结合强度，对于改进基于分子受体的提取、传感器技术的进步、晶体工程和超分子化学非常有用。本研究主要在FC-72（一种全氟己烷混合物）中研究杂环碱与末端羧酸基团的全氟聚醚（Krytox 157FSH(1)）之间的氢键。我们特别感兴趣的是，在氢键配合物中，质子转移是否发生，如果发生，在什么条件下发生。连续变化实验表明，在FC-72中，弱碱（吡嗪、嘧啶和喹唑啉）与1形成1:1的配合物，而强碱（喹啉、吡啶和异喹啉）与1形成1:3的配合物。紫外和红外光谱特征表明，1:1配合物为分子（B-HA），而1:3配合物为离子（BH+中心点A(-) HAHA）。详细讨论了1:3离子配合物的红外光谱。本文整理了n -杂环碱与羧酸在一系列溶剂中配合物的文献和实验数据，比较溶剂对质子转移的影响。极性溶剂以1:1的摩尔比支持离子氢键。在非极性有机溶剂中，离子氢键仅在1:2（碱/酸）化学计量的配合物中观察到。在含氟溶剂中，为了促进羧酸和所研究的碱之间氢键中的质子转移，需要更大的酸过量（1:3）。
There are only a few studies of noncovalent association in fluorous solvents and even fewer that are quantitative. A full understanding, particularly of stoichiometry and binding strength of noncovalent interactions in fluorous solvents could be very useful in improved molecular-receptor-based extractions, advancements in sensor technologies, crystal engineering, and supramolecular chemistry. This work investigates hydrogen bonding between heterocyclic bases and a perfluoropolyether with a terminal carboxylic acid group (Krytox 157FSH (1)), chiefly in FC-72 (a mixture of perfluorohexanes). In particular, we were interested in whether or not proton transfer occurs, and if so, under what conditions in H-bonded complexes. Continuous variations experiments show that in FC-72 weaker bases (pyrazine, pyrimidine, and quinazoline) form 1:1 complexes with 1, whereas stronger bases (quinoline, pyridine, and isoquinoline) form 1:3 complexes. Ultraviolet and infrared spectral signatures reveal that the 1:1 complexes are molecular (B-HA) whereas the 1:3 complexes are ionic (BH+center dot A(-) HAHA). Infrared spectra of 1:3 ionic complexes are discussed in detail. Literature and experimental data on complexes between N-heterocyclic bases and carboxylic acids in a range of solvents are compiled to compare solvent effects on proton transfer. Polar solvents support ionic hydrogen bonds at a 1:1 mol ratio. In nonpolar organic solvents, ionic hydrogen bonds are only observed in complexes with 1:2 (base/acid) stoichiometries. In fluorous solvents, a larger excess of acid, 1:3, is necessary to facilitate proton transfer in hydrogen bonds between carboxylic acids and the bases studied.