作者:Victor Vargas、Luis Amigo
DOI:10.1039/b101041g
日期:——
We have studied the enol-imine→keto-amine tautomeric equilibrium of N-salicylidene-p-X-aniline compounds with X = Me, OMe, NMe2 as electron donor substituents and X = COMe, CN and NO2 as electron acceptor substituents. The equilibrium constants (K°tau) and standard thermodynamic properties ΔG°tau, ΔH°tau and ΔS°tau were measured and calculated in methanol solution at various temperatures, by means of excitation fluorescence spectroscopy. We have analyzed the p-phenylaniline substitution effect on K°tau and the thermodynamic properties through the Hammett parameters σ. We have performed molecular orbital calculations at the semiempirical AM1 and ab initio HF/3-21G levels to interpret the experimental results, explicitly including the solute–solvent interaction through the formation of an intermolecular hydrogen bond between the salicylidene and methanol molecules. These computational results show a good correlation with the experimental values. An interpretation of the experimental values of TΔS°, based on changes in the molecular structure produced in the enol-imine→keto-amine tautomeric reaction, is proposed.
我们研究了以 X = Me、OMe、NMe2 为电子给体取代基和以 X = COMe、CN 和 NO2 为电子受体取代基的 N-水杨酰-p-X-苯胺化合物的烯醇-亚胺→酮胺同分异构平衡。通过激发荧光光谱法,我们测量并计算了不同温度下甲醇溶液中的平衡常数(K°tau)和标准热力学性质ΔG°tau、ΔH°tau 和 ΔS°tau。我们通过哈米特参数 σ 分析了对苯胺取代对 K°tau 和热力学性质的影响。我们在半经验 AM1 和 ab initio HF/3-21G 水平上进行了分子轨道计算,以解释实验结果,其中明确包括通过水杨烯分子和甲醇分子之间形成分子间氢键而产生的溶质-溶剂相互作用。这些计算结果与实验值显示出良好的相关性。根据烯醇-亚胺→酮-胺同分异构反应中产生的分子结构变化,提出了对 TΔS° 实验值的解释。