Semenov Valentin A, Samultsev Dmitry O, Krivdin Leonid B
A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, Irkutsk, Russia.
Magn Reson Chem. 2019 Jul;57(7):346-358. doi: 10.1002/mrc.4851. Epub 2019 Mar 18.
A systematic density functional theory (DFT) study of the accuracy factors (functionals, basis sets, and solvent effects) for the computation of N NMR chemical shifts has been performed in the series of condensed nitrogen-containing heterocycles. The behavior of the most representative functionals was examined based on the benchmark calculations of N NMR chemical shifts in the reference set of compounds. It was found that the best agreement with experiment was achieved with OLYP functional in combination with aug-pcS-3(N)//pc-2 locally dense basis set scheme providing mean absolute error of 5.2 ppm in the range of about 300 ppm. Taking into account solvent effects was performed within a general Tomasi's polarizable continuum model scheme. It was also found that computationally demanding supermolecular solvation model computations essentially improved some "difficult" cases, as was illustrated with phenanthroline dissolved in methanol. Based on the performed calculations, some 200 unknown N NMR chemical shifts were predicted with a high level of confidence for about 50 real-life condensed nitrogen-containing heterocycles, which could serve as a practical guide in structural elucidation of this class of compounds.
已对一系列稠合含氮杂环化合物进行了关于¹⁵N核磁共振化学位移计算的精度因素（泛函、基组和溶剂效应）的系统密度泛函理论（DFT）研究。基于化合物参考集中¹⁵N核磁共振化学位移的基准计算，考察了最具代表性泛函的行为。结果发现，使用OLYP泛函结合aug-pcS-3(N)//pc-2局部致密基组方案时，与实验结果的吻合度最佳，在约300 ppm范围内平均绝对误差为5.2 ppm。在通用的托马西极化连续介质模型方案中考虑了溶剂效应。还发现，计算量较大的超分子溶剂化模型计算在本质上改善了一些“困难”情况，如菲咯啉溶解在甲醇中的情况所示。基于所进行的计算，对约50种实际的稠合含氮杂环化合物，以高度置信度预测了约200个未知的¹⁵N核磁共振化学位移，这可为这类化合物的结构解析提供实用指导。
