Department of Chemical Sciences , Indian Institute of Science Education and Research Mohali , Sector 81, Knowledge City, S.A.S.Nagar , Manauli , 140306 Punjab , India.
J Org Chem. 2018 Apr 20;83(8):4307-4322. doi: 10.1021/acs.joc.7b02604. Epub 2018 Apr 9.
The electronic and steric effects of aryl substituents and the influence of hydrogen bonding in Z-isomer stability of phenylazopyrazole derivatives have been investigated. In this regard, 38 substituted phenylazopyrazole derivatives and 6 N-methyl phenylazopyrazoles (with meta substitutions) have been synthesized. Their photoswitching behavior, photostationary states (PSS), and kinetics of thermal reverse isomerization were evaluated experimentally using UV-vis and NMR spectroscopic techniques. Furthermore, density functional theory (DFT) computations have been performed for more detailed insights. Despite the presence of substantial substituent effects inferred through Taft and Hammett relationships, the concentration dependency in controlling the isomerization rates has also been observed. Kinetics studies at different concentrations, solvent effects, and computations have confirmed the decisive role of hydrogen bonding and solvent-assisted tautomerism in this regard. Through this study, a complex interplay of steric, electronic effects and hydrogen bonding as factors in dictating the stability of Z-isomers in arylazo-1 H-3,5-dimethylpyrazoles has been demonstrated.
研究了芳基取代基的电子和空间效应以及氢键对苯基偶氮吡唑衍生物 Z 型异构体稳定性的影响。为此，合成了 38 个取代的苯基偶氮吡唑衍生物和 6 个 N-甲基苯基偶氮吡唑（间位取代）。使用紫外-可见和 NMR 光谱技术实验评估了它们的光致开关行为、光稳定态（PSS）和热反式异构化动力学。此外，还进行了密度泛函理论（DFT）计算以获得更详细的见解。尽管通过 Taft 和 Hammett 关系推断出存在大量取代基效应，但也观察到了浓度依赖性对控制异构化速率的影响。在不同浓度、溶剂效应和计算条件下的动力学研究证实了氢键和溶剂辅助互变异构在这方面的决定性作用。通过这项研究，证明了在芳基偶氮-1H-3,5-二甲基吡唑中，空间、电子效应和氢键作为决定 Z 型异构体稳定性的因素之间存在复杂的相互作用。
