CCMAR and Department of Chemistry and Pharmacy, FCT, Campus de Gambelas, University of Algarve, 8005-039 Faro, Portugal.
Department of Chemistry, University of Liverpool, Liverpool L69 7ZD, UK.
Molecules. 2021 Jul 15;26(14):4299. doi: 10.3390/molecules26144299.
The prototropic tautomerism in 3(5)-aminopyrazoles was investigated by matrix isolation infrared (IR) spectroscopy, supported by DFT(B3LYP)/6-311++G(d,p) calculations. In consonance with the experimental data, the calculations predict tautomer 3-aminopyrazole (3AP) to be more stable than the 5-aminopyrazole (5AP) tautomer (calculated energy difference: 10.7 kJ mol; Gibbs free energy difference: 9.8 kJ mol). The obtained matrix isolation IR spectra (in both argon and xenon matrices) were interpreted, and the observed bands were assigned to the tautomeric forms with help of vibrational calculations carried out at both harmonic and anharmonic levels. The matrix-isolated compound (in argon matrix) was then subjected to in situ broadband UV irradiation (λ > 235 nm), and the UV-induced transformations were followed by IR spectroscopy. Phototautomerization of the 3AP tautomer into the 5AP form was observed as the strongly prevalent reaction.
采用矩阵隔离红外（IR）光谱法结合 DFT（B3LYP）/6-311++G（d，p）计算研究了 3（5）-氨基吡唑的互变异构现象。与实验数据一致，计算预测 3-氨基吡唑（3AP）异构体比 5-氨基吡唑（5AP）异构体更稳定（计算的能量差：10.7 kJ/mol；吉布斯自由能差：9.8 kJ/mol）。解释了获得的基质隔离红外光谱（在氩气和氙气基质中），并借助在谐波和非谐波水平上进行的振动计算，将观察到的谱带分配给互变异构形式。然后将基质隔离化合物（在氩气基质中）进行原位宽带 UV 辐射（λ>235nm），并通过 IR 光谱跟踪 UV 诱导的转化。观察到 3AP 互变异构体向 5AP 形式的光互变异构反应是主要的反应。
