Samultsev Dmitry O, Rusakov Yury Yu, Krivdin Leonid B
A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, Favorsky St. 1, Irkutsk, 664033, Russia.
Magn Reson Chem. 2017 Nov;55(11):990-995. doi: 10.1002/mrc.4618. Epub 2017 Jun 21.
Long-range β- and γ-relativistic effects of halogens in N NMR chemical shifts of 20 halogenated azines (pyridines, pyrimidines, pyrazines, and 1,3,5-triazines) are shown to be unessential for fluoro-, chloro-, and bromo-derivatives (1-2 ppm in average). However, for iodocontaining compounds, β- and γ-relativistic effects are important contributors to the accuracy of the N calculation. Taking into account long-range relativistic effects slightly improves the agreement of calculation with experiment. Thus, mean average errors (MAE) of N NMR chemical shifts of the title compounds calculated at the non-relativistic and full 4-component relativistic levels in gas phase are accordingly 7.8 and 5.5 ppm for the range of about 150 ppm. Taking into account solvent effects within the polarizable continuum model scheme marginally improves agreement of computational results with experiment decreasing MAEs from 7.8 to 7.4 ppm and from 5.5 to 5.3 ppm at the non-relativistic and relativistic levels, respectively. The best result (MAE: 5.3 ppm) is achieved at the 4-component relativistic level using Keal and Tozer's KT3 functional used in combination with Dyall's relativistic basis set dyall.av3z with taking into account solvent effects within the polarizable continuum solvation model. The long-range relativistic effects play a major role (of up to dozen of parts per million) in N NMR chemical shifts of halogenated nitrogen-containing heterocycles, which is especially crucial for iodine derivatives. This effect should apparently be taken into account for practical purposes.
结果表明，对于20种卤代嗪（吡啶、嘧啶、吡嗪和1,3,5 - 三嗪）的氮核磁共振化学位移，卤素的长程β和γ相对论效应对于氟代、氯代和溴代衍生物（平均为1 - 2 ppm）而言并不重要。然而，对于含碘化合物，β和γ相对论效应是氮计算准确性的重要贡献因素。考虑长程相对论效应会略微提高计算值与实验值的吻合度。因此，在气相中，在非相对论和全四分量相对论水平下计算得到的标题化合物氮核磁共振化学位移的平均绝对误差（MAE），在约150 ppm的范围内分别为7.8和5.5 ppm。在极化连续介质模型方案中考虑溶剂效应，会略微提高计算结果与实验值的吻合度，在非相对论和相对论水平下，MAE分别从7.8降至7.4 ppm以及从5.5降至5.3 ppm。使用Keal和Tozer的KT3泛函与Dyall的相对论基组dyall.av3z相结合，并在极化连续介质溶剂化模型中考虑溶剂效应，在四分量相对论水平下可得到最佳结果（MAE：5.3 ppm）。长程相对论效应在卤代含氮杂环的氮核磁共振化学位移中起主要作用（高达百万分之几十），这对于碘衍生物尤为关键。出于实际目的，显然应考虑这种效应。
