Department of Chemistry, University of Sheffield, Sheffield, (UK)S3 7HF.
Org Biomol Chem. 2010 Apr 21;8(8):1943-50. doi: 10.1039/b927107d.
Changes in the (31)P NMR chemical shift of tri-n-butylphosphine oxide have been measured as function of solvent composition in a number of binary solvent mixtures. The data were analysed using a model that separates the contributions of specific H-bond interactions with the first solvation shell and the non-specific effects of the bulk solvent on the chemical shift. This allowed measurement of equilibrium constants between differently solvated states of the probe and hence thermodynamic quantification of preferential solvation in the binary mixtures. The results are analysed in the context of the electrostatic solvent competition model, which assumes that solvent effects on intermolecular interactions can be interpreted based on the exchange of specific functional group contacts, with minimal involvement of the bulk solvent. The thermodynamic measurements of preferential solvation were used to determine the H-bond donor parameter alpha for cyclohexane, n-octane, n-dodecane, benzene, 1,4-dioxane, carbon tetrachloride, acetone, dichloromethane, dimethyl sulfoxide and chloroform. For solvents where the H-bond donor parameters have been measured as solutes in carbon tetrachloride solution, the H-bond donor parameters measured here for the same compounds as solvents are practically identical, i.e. solute and solvent H-bond parameters are directly interchangable. For alkanes, the experimental H-bond donor parameter is significantly larger than expected based on calculated molecular electrostatic potential surfaces. This might suggest an increase in the relative importance of van der Waals interactions when electrostatic effects are weak.
三正丁基氧化膦在若干二元溶剂混合物中，其（31）P NMR 化学位移随溶剂组成的变化已被测定。数据使用一种模型进行了分析，该模型将与第一溶剂化壳层的特定氢键相互作用的贡献与溶剂对化学位移的非特异性影响分离开来。这允许测量探针不同溶剂化状态之间的平衡常数，从而对二元混合物中的优先溶剂化进行热力学量化。结果在静电溶剂竞争模型的背景下进行了分析，该模型假设可以根据特定官能团接触的交换来解释溶剂对分子间相互作用的影响，而无需涉及大量溶剂。优先溶剂化的热力学测量用于确定环己烷、正辛烷、正十二烷、苯、1,4-二恶烷、四氯化碳、丙酮、二氯甲烷、二甲基亚砜和氯仿的氢键供体参数α。对于在四氯化碳溶液中作为溶质测量氢键供体参数的溶剂，这里对于相同化合物作为溶剂测量的氢键供体参数实际上是相同的，即溶质和溶剂氢键供体参数可以直接互换。对于烷烃，实验氢键供体参数明显大于根据计算分子静电势表面预测的预期值。这可能表明当静电效应较弱时，范德华相互作用的相对重要性增加。
