Solvent Effects on Chemical Exchange in a Push–Pull Ethylene as Studied by NMR and Electronic Structure Calculations
作者:Maysoon Ababneh-Khasawneh、Blythe E. Fortier-McGill、Marzia E. Occhionorelli、Alex D. Bain
DOI:10.1021/jp201885q
日期:2011.7.7
conformation in solution must be due to entropic effects. Similarly, the solvent effect on the E-Z barrier is primarily due to entropy. The measured enthalpy of activation is similar in all the solvents, but the entropy of activation increases with the solvent polarity. The barrier to rotation of the N,N-dimethylamino group shows a combination of entropy and enthalpy effects. This combination of experiments and
给出了溶解在许多不同溶剂中的推挽式乙烯中化学交换的NMR测量结果。这些都通过使用气相条件和模拟溶剂的高级电子结构计算进行补充。结果表明,必须包含熵效应才能了解观察到的趋势。例如,在这种情况下,平衡状态表示必须具有最低吉布斯自由能的状态,而不是最低焓。具体的分子是3-二甲基氨基-2-氰基巴豆酸甲酯(MDACC)。碳-碳双键的几何形状可以是E或Z在环境温度下人口大致相等。我们已经在许多溶剂中测量了平衡常数和这些状态之间的交换速率:甲醇,氯仿,乙腈,甲苯,二氯甲烷,丙酮和四氢呋喃。此外,连接至双键的N,N-二甲基氨基也显示出受限的旋转,并且这已经在E和Z构象中进行了测量。平衡常数和三个旋转壁垒为溶剂效果提供了出色的探索。使用Hartree-Fock方法和密度泛函(B3LYP)方法对电子结构进行计算,其基数设置为6-311 ++ G(2df,2p),用于预测E。和Z基态,以及三个过渡态。计算是针对