N-烷基吡啶阳离子及其与若干阴离子形成的离子对结构的理论研究

采用密度泛函理论方法, 在B3LYP/6-31＋G(d) 水平上研究了吡啶、N-烷基吡啶阳离子及其与若干阴离子(F^－, Cl^－, Br^－, , )形成的离子对的稳定构型. 计算结果表明: N-烷基吡啶阳离子的吡啶环与中性吡啶分子类似, 具有芳香性, 烷基对吡啶环结构影响不大; 离子对中阴离子易出现在吡啶环上方以及C(5)—H 或C(2)—H 和 N-甲基附近; 阴、阳离子之间通常存在多重氢键, 并且均有部分电荷转移; 离子对的相互作用能随着N-烷基的增长而减小.

Theoretical Study of the Structural Characterizations of N-Alkylpyridinium Cations and Their Ion-pairs with Some Anions

The stable geometries of pyridine, N-alkylpyridinium cations, and the ion-pairs of N-alkylpyridinium cations with F^－, Cl^－, Br^－, and have been investigated by performing density functional theory calculations at the B3LYP/6-31＋G(d) level. The calculated results indicate that the structure of the pyridine ring in N-alkylpyridinium cations is generally similar to that of the neutral pyridine molecule, i.e. the pyridine ring retains its aromaticity, and the N-alkyl side chain has little effect on the structures of the pyridine ring. It was also found that the anions were inclined to move to the vicinities of the C(5)—H fragment or between C(2)—H and N-methyl above the pyridinium ring in ionic liquids. There are always multiple H-bondings between the anion and cation with partial charge transfer. Furthermore, the longer the N-alkyl side chain is, the weaker the hydrogen bond between the cation and anion will be.