Raczyńska Ewa Daniela, Maria Pierre-Charles, Gal Jean-François
Department of Chemistry, Warsaw University of Life Sciences (SGGW), ul. Nowoursynowska 159c, 02-776 Warsaw, Poland.
Institut de Chimie de Nice, University Côte d'Azur, UMR 7272 CNRS, Parc Valrose, 06108 Nice, France.
Molecules. 2025 May 9;30(10):2112. doi: 10.3390/molecules30102112.
In the quest of the pivotal origin of the very strong gas-phase proton basicity for some iminopyrrole derivatives, proposed in the literature on the basis of quantum chemical calculations, the full tautomeric and acid/base equilibria were investigated in vacuo for 2-aminopyrrole exhibiting enamino-imino tautomerism. Thermochemistry of these processes investigated at the Density Functional Theory (DFT) level indicates a lower stability for the imino than for the enamino tautomers. However, the imino N atom in the imino forms displays an exceptionally high basicity, particularly in the minor and rare tautomers containing at least one tautomeric proton at the pyrrole C atom. This explains why derivatives of CH tautomers (being free of prototropy) display exceptionally high gas-phase proton basicity. As predicted by the Maksić group using quantum chemical methods, these derivatives can be considered as good organic imino N-superbase candidates. Unfortunately, some other structures of iminopyrrole derivatives (proposed by the same group) possess labile protons, and, thus, exhibit prototropy, resulting in the transformation into the more stable but less basic aminopyrrole derivatives under synthesis conditions or acid/base equilibria measurements.
在探寻某些亚氨基吡咯衍生物极强气相质子碱度的关键来源时（文献基于量子化学计算提出），对表现出烯胺 - 亚胺互变异构的2 - 氨基吡咯在真空中的完整互变异构和酸碱平衡进行了研究。在密度泛函理论（DFT）水平上对这些过程的热化学研究表明，亚胺互变异构体的稳定性低于烯胺互变异构体。然而，亚胺形式中的亚胺氮原子表现出异常高的碱度，特别是在吡咯碳原子上至少含有一个互变异体质子的次要且罕见的互变异构体中。这解释了为什么CH互变异构体（无质子转移）的衍生物表现出异常高的气相质子碱度。正如马克西奇小组用量子化学方法所预测的，这些衍生物可被视为良好的有机亚胺氮超强碱候选物。不幸的是，亚氨基吡咯衍生物的其他一些结构（由同一小组提出）具有不稳定质子，因此表现出质子转移，导致在合成条件或酸碱平衡测量下转化为更稳定但碱性较弱的氨基吡咯衍生物。
