物理化学学报 >> 2004, Vol. 20 >> Issue (08S): 911-916.doi: 10.3866/PKU.WHXB200408zk04

研究论文 上一篇    下一篇

基态丙酮酸单分子反应的机理

丁万见;方维海;刘若庄   

  1. 北京师范大学化学系,北京 100875
  • 收稿日期:2003-11-11 修回日期:2004-01-06 发布日期:2004-08-15
  • 通讯作者: 刘若庄 E-mail:rzliu@bnu.edu.cn

Mechanisms of Unimolecular Reactions for Ground-state Pyruvic Acid

Ding Wan-Jian;Fang Wei-Hai;Liu Ruo-Zhuang   

  1. Department of Chemistry, Beijing Normal University, Beijing 100875
  • Received:2003-11-11 Revised:2004-01-06 Published:2004-08-15
  • Contact: Liu Ruo-Zhuang E-mail:rzliu@bnu.edu.cn

摘要: 运用MP2和B3LYP方法,对基态丙酮酸的8个可能的单分子反应的反应机理进行了详细的理论计算. 研究发现,氢键相互作用及两个羰基的相对空间取向在丙酮酸异构体的稳定性中起着重要的作用. 并且由最稳定的异构体Tc旋转为其它异构体的能垒都比较高,旋转异构反应在室温下是难于进行的. 经由质子迁移过程可实现Ct和Tt异构体之间的转化,但反应能垒比内旋转过程高得多,说明质子迁移无法与内旋转过程相竞争. 对基态丙酮酸脱羧和脱羰反应途径的研究均表明,脱羧反应是经由五中心过渡态首先生成甲基羟基卡宾中间体,然后中间体再进一步异构得到产物. 四中心协同反应机理是不利的.

关键词: 丙酮酸, 异构, 脱羧, 脱羰, 反应机理

Abstract: Eight possible unimolecular reaction pathways for ground-state pyruvic acid(PA) have been investigated in this work at the MP2/cc-pVDZ and B3LYP/cc-pVDZ levels of theory. The results indicate that hydrogen bond interaction and relative orientation of the two carbonyl groups play an important role in the stability of pyruvic acid rotamers. Moreover, the barriers for Tc isomerization to other isomers through internal rotation are high, suggesting that the isomerization reactions occur difficultly at room temperature. The barrier for transformation of Ct and Tt isomers through proton migration is higher than that through internal rotation, showing that the former cannot compete with the later. Under the investigation on decarboxylation and decarbonylation reactions, it can be concluded that the decarboxylation reaction takes place through stepwise mechanism involved in a five-center transition state and produces methyl hydroxycarbene firstly, and the concerted mechanism associated with a four-center transition state is disadvantageous.

Key words: Pyruvic acid, Isomerization, Decarboxylation, Decarbonylation, Reaction mechanism