Department of Chemistry, Katholieke Universiteit Leuven, Heverlee, Belgium.
J Phys Chem B. 2011 Jul 7;115(26):8424-38. doi: 10.1021/jp2027675. Epub 2011 Jun 10.
Two series of 1-alkylpyridinium and N-alkyl-N-methylpiperidinium ionic liquids functionalized with a nitrile group at the end of the alkyl chain have been synthesized. Structural modifications include a change of the alkyl spacer length between the nitrile group and the heterocycle of the cationic core, as well as adding methyl or ethyl substituents on different positions of the pyridinium ring. The anions are the bromide and the bis(trifluoromethylsulfonyl)imide ion. All the bis(trifluoromethylsulfonyl)imide salts as well as the bromide salts with a long alkyl spacer were obtained as viscous liquids at room temperature, but some turned out to be supercooled liquids. In addition, pyrrolidinium and piperidinium ionic liquids with two nitrile functions attached to the heterocyclic core have been prepared. The crystal structures of seven pyridinium bis(trifluoromethylsulfonyl)imide salts are reported. Quantum chemical calculations have been performed on model cations and ion pairs with the bis(trifluoromethylsulfonyl)imide anion. A continuum model has been used to take solvation effects into account. These calculations show that the natural partial charge on the nitrogen atom of the nitrile group becomes more negative when the length of the alkyl spacer between the nitrile functional group and the heterocyclic core of the cation is increased. Methyl or methoxy substituents on the pyridinium ring slightly increase the negative charge on the nitrile nitrogen atom due to their electron-donating abilities. The position of the substituent (ortho, meta, or para) has only a very minor effect on the charge of the nitrogen atom. The (15)N NMR spectra of the bis(trifluoromethylsulfonyl)imide ionic liquids were recorded with the nitrogen-15 nucleus at its natural abundance. The chemical shift of the (15)N nucleus of the nitrile nitrogen atom could be correlated with the calculated negative partial charge on the nitrogen atom.
已经合成了两系列的 1-烷基吡啶鎓和 N-烷基-N-甲基哌啶鎓离子液体，它们在烷基链的末端带有腈基。结构修饰包括改变腈基和阳离子核心杂环之间的烷基间隔长度，以及在吡啶环的不同位置上添加甲基或乙基取代基。阴离子是溴化物和双（三氟甲烷磺酰）亚胺离子。所有的双（三氟甲烷磺酰）亚胺盐以及具有长烷基间隔的溴化物盐在室温下都是粘性液体，但有些则是过冷液体。此外，还制备了带有两个腈基官能团连接到杂环核心的吡咯烷鎓和哌啶鎓离子液体。报道了七种吡啶双（三氟甲烷磺酰）亚胺盐的晶体结构。对带有双（三氟甲烷磺酰）亚胺阴离子的模型阳离子和离子对进行了量子化学计算。使用连续模型考虑溶剂化效应。这些计算表明，当腈基官能团与阳离子的杂环核心之间的烷基间隔长度增加时，腈基氮原子上的自然部分电荷变得更负。吡啶环上的甲基或甲氧基取代基由于其供电子能力而略微增加了腈基氮原子上的负电荷。取代基的位置（邻位、间位或对位）对氮原子的电荷只有很小的影响。用氮-15 核在其自然丰度下记录了双（三氟甲烷磺酰）亚胺离子液体的（15）N NMR 谱。腈基氮原子的（15）N 核的化学位移可以与计算得出的氮原子的负部分电荷相关联。
