School of Chemistry, University of New South Wales , Sydney, New South Wales 2052, Australia.
J Org Chem. 2017 Jul 21;82(14):7324-7331. doi: 10.1021/acs.joc.7b00716. Epub 2017 Jul 3.
A range of more than 25 imidazolium salts, chosen for their differing steric and electronic features, were prepared, and their pK values were determined using the bracketing indicator method. Through the systematic change in the structure of the imidazolium cation, the effect of varying substituents at each position on the heterocyclic ring was determined; particularly, the transmission of electronic effects was quantified using Hammett parameters. These new data give an indication of the strength of base required for deprotonation and the potential to correlate these data with the nucleophilicity of the corresponding carbenes.
制备了一系列超过 25 种的咪唑鎓盐，选择它们是因为其具有不同的空间位阻和电子特性，并使用内标指示剂法测定了它们的 pK 值。通过系统改变咪唑鎓阳离子的结构，确定了杂环环上每个位置的取代基变化的影响；特别是，使用哈米特参数量化了电子效应的传递。这些新数据表明了所需的去质子化碱的强度，并有可能将这些数据与相应碳烯的亲核性相关联。
