大多数腙化合物更喜欢吖嗪互变异构态。然而,氧/硫取代的化合物更喜欢腙互变异构体。在这项研究中,M062X水平的密度泛函理论,基集为6-311++g(2d,2p),以MP2/cc-pVTZ为参考,用于研究腙和吖嗪形式与氧的不同互变异构机理,硫磺,碳,和氮作为负中心。相对于其吖嗪互变异构结构,能量稳定性的顺序为氧-<硫-<亚胺-<脒基-<卡宾-取代的腙。分子结构的共振可能是其能量稳定性的几何基础,并根据HOMED指数进行估算。Further,作为羟基<巯基<亚胺末端基团的趋势中增加的质子亲和力解释了它们增加的吖嗪偏好。通过计算H转移的跃迁能垒,检查了从嗪到腙的可逆平衡的质子释放。有利于形成含氧和含硫基团的腙互变异构体,而对于氨基取代的则不太有利。叠氮形式是甲基取代的最稳定的互变异构体。
Most hydrazone compounds prefer the
azine tautomeric states. However, oxygen-/sulfur-substituted compounds prefer hydrazone tautomers. In this study, density functional theory at M062X level with the basis set of 6-311 + + g(2d, 2p), with MP2/cc-pVTZ for reference, was used to investigate the different tautomeric mechanisms between hydrazone and
azine forms with oxygen, sulfur, carbon, and nitrogen as negative centers. The energetic stabilities are in the order as oxygen- < sulfur- < imine- < amidino- < carbene-substituted hydrazones with respect to their
azine tautomeric structures. Resonance of the molecular structures might be the geometrical basis for their energy stabilities and were estimated based on HOMED indices. Further, the increased proton affinities in the trend as hydroxyl < sulfhydryl < imine terminal groups account for their increasing azine preferences. Proton release was examined for the reversible equilibrium from
azine to hydrazone by calculating the transition energy barrier of H transfer. It is favorable to form hydrazone tautomers for oxygen and sulfur containing groups, while it is less favorable for amino-substituted ones.
Azine form is the most stable tautomer for methyl substituted.