NMR Study of Solvation Effect on the Geometry of Proton-Bound Homodimers of Increasing Size

Hydrogen bond geometries in the proton-bound homodimers of quinoline and acridine derivatives in an aprotic polar solution have been experimentally studied using 1H NMR at 120 K. The reported results show that an increase of the dielectric permittivity of the medium results in contraction of the N···N distance. The degree of contraction depends on the homodimer’s size and its substituent-specific solvation features. Neither of these effects can be reproduced using conventional implicit solvent models employed in computational studies. In general, the N···N distance in the homodimers of pyridine, quinoline, and acridine derivatives decreases in the sequence gas phase > solid state > polar solvent.本实验针对非质子极性溶剂中喹啉与吖啶衍生物的质子键合同二聚体的氢键几何构型展开研究，于120 K下采用1H核磁共振波谱法（¹H NMR）完成测试。研究结果表明，介质介电常数的升高会使N···N距离缩短；该缩短程度取决于同二聚体的尺寸以及其取代基特异性的溶剂化特性。常规计算研究中所使用的隐式溶剂模型，均无法复现上述任一效应。总体而言，吡啶、喹啉与吖啶衍生物同二聚体中的N···N距离遵循如下递减顺序：气相 > 固态 > 极性溶剂。