p-羟基苯丙酮酸互变异构反应机理溶剂效应的理论研究

Theoretical Investigation on the Solvent Effect of Tautomerization Reaction Mechanism of p-Hydroxyphenylpyruvic Acid

采用密度泛函B3LYP方法,在6-31+G**基组水平上对p-羟基苯丙酮酸质子转移引起的烯醇式-酮式互变异构反应机理进行了计算研究,获得了互变异构过程的反应焓、活化能、活化吉布斯自由能和质子转移反应的速率常数等参数。Onsager反应场溶剂模型用于水相和甲醇相的计算,计算结果表明,p-羟基苯丙酮酸无论在气相还是水相、甲醇相中,其酮式异构体都是最稳定的存在形式,烯醇式异构体也会以一定量共存。气相中孤立分子内质子转移几何构型改变较显著,异构化反应需要较大的活化能,不利于发生质子转移,Onsager模型计算方法对质子转移反应的影响较小。

The reaction mechanisms of keto-enol tautomerization on p-hydroxyphenylpyruvic acid resulted from proton transfer were investigated using DFT-B3LYP method with 6-31＋G ＊＊ basis set.Zero point energies,total energies,Gibbs free energies,reaction enthalpies,activation energies,activation Gibbs free energies and the rate constants of tautomerization reactions were obtained.The calculations in the aqueous phase and methanol phase were carried out using Onsager model.The results showed that the keto form of p-hydroxyphenylpyruvic acid is the most stable either in the gas phase or the solution phase with water and methanol as solvent.The enol tautomer can be co-existed in some.The change of geometrical configuration is very dramatic in intramolecular proton transfer in the gas phase and the larger energy barrier should be overcome for tautomerization reaction.