Departamento de Química, Laboratorio de Química Teórica, Universidad de Chile, Facultad de Ciencias, Casilla 653, Santiago, Chile.
J Phys Chem B. 2013 Feb 14;117(6):1911-20. doi: 10.1021/jp3114946. Epub 2013 Jan 30.
Two complementary models of Lewis molecular acidity are introduced and tested in a wide series of 45 room temperature ionic liquids (RTIL). They are defined in the context of the conceptual density functional theory. The first one, which we tentatively call the excess electronic chemical potential, assesses the electron accepting power of the RTIL by relating the H-bond donor acidity with the charge transfer associated to the acidic H-atom migration at the cation of the RTIL considered as a HB-donor species. This global index accounts for the molecular acidity of the cation moiety of the ionic liquid that takes into account the perturbation of the anionic partner. The second index is defined in terms of the local charge capacity modeled through the maximum electronic charge that the cation, in its valence state, may accept from an unspecified environment. Each model is compared with the experimental HB-donor acidity parameter of the Kamlet Taft model. The best comparison is obtained for a combination of both the excess electronic chemical potential and the local charge capacity. As expected, the correlations with the Kamlet Taft α parameter do not lead to a universal model of HB-donor acidity. Reduced correlations for limited series of structurally related RTIL are obtained instead. Finally, we illustrate the reliability and usefulness of the proposed model of RTIL molecular acidity to explain the cation-dependent solvent effects on the reactivity trends for cycloaddition, Kemp elimination, and Menschutkin reactions, for which experimental rate coefficients are available from literature.
引入并测试了两种互补的 Lewis 分子酸度模型，涵盖了 45 种室温离子液体 (RTIL)。这些模型是在概念密度泛函理论的背景下定义的。第一个模型，我们暂时称之为过剩电子化学势，通过将氢键供体酸度与与酸性 H 原子在 RTIL 阳离子中的迁移相关联的电荷转移联系起来，评估 RTIL 的电子接受能力，而 RTIL 阳离子被视为 HB-供体物种。这个全局指标考虑了离子液体阳离子部分的分子酸度，同时考虑了阴离子伴侣的扰动。第二个指数是根据局部电荷容量定义的，该容量通过阳离子在其价态下可能从指定环境中接受的最大电子电荷来建模。每个模型都与 Kamlet Taft 模型的实验 HB-供体酸度参数进行了比较。最佳比较是通过过剩电子化学势和局部电荷容量的组合获得的。正如预期的那样，与 Kamlet Taft α 参数的相关性并没有导致 HB-供体酸度的通用模型。相反，对于结构相关的 RTIL 的有限系列，得到了相关性降低的结果。最后，我们说明了所提出的 RTIL 分子酸度模型的可靠性和有用性，以解释阳离子依赖性溶剂对环加成、Kemp 消除和 Menschutkin 反应的反应性趋势的影响，对于这些反应，文献中提供了实验速率系数。
