取代羧酸和酮酸热消除机理的从头算研究(英)

Ab Initio Studies on the Thermal Elimination Mechanisms of Two Groups of Carboxylic Acids and Substituted Pyruvic Acids

利用从头计算方法研究了取代羧酸和酮酸的消除反应机理，结果表明，所有的脱羰过程均经历三元环过渡态，反应活性分别是：CH2FCOOH＞CH2＝CHCOOH＞CF3COOH＞CH3COOH和CF3COCOOH＞CH2FCOCOOH＞CH3COCOOH＞CH2＝CHCOCOOH，取代酮酸比羧酸的热消除更容易进行，α－酮酸的脱羧也已经被研究，其活化能比脱羰过程高得多。

Two series of carboxylic acid with or without a carbonyl group have been investi-gated by ab intio calculations for determining their elimination mechanisms and comparing their relative reactivities.The results show that all the decarbonylation proceed via a three-membered cyclic transition state.The trend of reactivity is CH2FCOOH>CH2=CHCOOH >CH3COOH>CH3COOH and CF3COCOOH>CH2FCOCOOH>CH3COCOOH>CH2=CHCOCOOH respectively.The thermal elimination of substituted pyruvic acids are more easily to happen than that of carboxylic acids.Another competing pathway,the decarboxyli-cation of an α-keto-acid has also been studied,its activation energy is higher than that of the decarbonylation process.