Faculty of Chemistry, University of Opole, Oleska 48, 45-052 Opole, Poland.
Molecules. 2019 Jul 19;24(14):2632. doi: 10.3390/molecules24142632.
A series of disubstituted 1-pyrazoles with methyl (), amino (), and nitro () groups, as well as ester () or amide () groups in positions 3 and 5 was synthesized, and annular tautomerism was investigated using X-ray, theoretical calculations, NMR, and FT-IR methods. The X-ray experiment in the crystal state showed for the compounds with methyl (, ) and amino () groups the tautomer with ester or amide groups at position 3 (tautomer 3), but for those with a nitro group (, ), tautomer 5. Similar results were obtained in solution by NMR NOE experiments in CDCl, DMSO-, and CDOD solvents. However, tautomer equilibrium was observed for in DMSO. The FT-IR spectra in chloroform and acetonitrile showed equilibria, which can be ascribed to conformational changes of the cis/trans arrangement of the ester/amide group and pyrazole ring. Theoretical analysis using the M06-2X/6-311++G(d,p) method (in vacuo, chloroform, acetonitrile, and water) and measurement of aromaticity (NICS) showed dependence on internal hydrogen bonds, the influence of the environment, and the effect of the substituent. These factors, pyrazole aromaticity and intra- and inter-molecular interactions, seem to have a considerable influence on the choice of tautomer.
合成了一系列带有甲基（）、氨基（）和硝基（）取代基的 1-吡唑，并在 3 位和 5 位带有酯（）或酰胺（）取代基，采用 X 射线、理论计算、NMR 和 FT-IR 方法研究了其环形互变异构现象。X 射线晶体实验表明，对于带有甲基（、）和氨基（）取代基的化合物，其 3 位带有酯基或酰胺基的互变异构体 3（互变异构体 3），但对于带有硝基取代基（、）的化合物，则为互变异构体 5。在 CDCl、DMSO-和 CDOD 溶剂中的 NMR NOE 实验也在溶液中得到了类似的结果。然而，在 DMSO 中观察到了互变异构平衡。在氯仿和乙腈中的 FT-IR 光谱显示出平衡，可以归因于酯/酰胺基团和顺/反式排列的构象变化。使用 M06-2X/6-311++G(d,p)方法（在真空、氯仿、乙腈和水中）进行理论分析以及芳香性（NICS）的测量表明，互变异构体的选择取决于内部氢键、环境的影响以及取代基的影响。这些因素，如吡唑的芳香性、分子内和分子间相互作用，似乎对互变异构体的选择有相当大的影响。
