Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic , Flemingovo nam. 2, 166 10 Prague, Czech Republic.
Faculty of Science, Charles University , 116 36 Prague, Czech Republic.
J Org Chem. 2017 Oct 6;82(19):10350-10359. doi: 10.1021/acs.joc.7b01810. Epub 2017 Sep 8.
Intramolecular hydrogen bonds (IMHBs) in 5-azopyrimidines are investigated by NMR spectroscopy and DFT computations that involve nuclear quantum effects. A series of substituted 5-phenylazopyrimidines with one or two hydrogen bond donors able to form IMHBs with the azo group is prepared by azo coupling. The barrier of interconversion between two rotamers of the compounds with two possible IMHBs is determined by variable temperature NMR spectroscopy and it is demonstrated that the barrier is significantly affected by intramolecular charge transfer. Through-hydrogen-bond scalar coupling is investigated in N labeled compounds and the stability of the IMHBs is correlated with experimental NMR parameters and rationalized by path integral molecular dynamics simulations that involve nuclear quantum effects. Detailed information on the hydrogen bond geometry upon hydrogen-to-deuterium isotope exchange is obtained from a comparison of experimental and calculated NMR data.
通过核磁共振波谱和涉及核量子效应的密度泛函理论计算研究了 5-偶氮嘧啶中的分子内氢键 (IMHBs)。通过偶联反应合成了一系列带有一个或两个能够与偶氮基团形成 IMHBs 的氢键供体的取代 5-苯基偶氮嘧啶。通过变温核磁共振波谱法确定了具有两个可能的 IMHBs 的化合物的两个旋光异构体之间的互变的能垒，结果表明，该能垒受分子内电荷转移的显著影响。通过 N 标记化合物研究了通过氢键的标量耦合，并且通过涉及核量子效应的路径积分分子动力学模拟将 IMHBs 的稳定性与实验 NMR 参数相关联并合理化。通过比较实验和计算 NMR 数据，获得了氢到氘同位素交换时氢键几何形状的详细信息。
