How Effective Is the Single-point Energy Calculation in Investigating the Reaction Mechanisms?New Decarboxylation Mechanism of Pyrrole-2-carboxylic Acid by Full Optimization with CPCM Solvation Model  

作　　者：程学礼 赵燕云 何国芳 李丽清 韩银峰 吴仁涛 

机构地区：[1]School of Chemistry and Chemical Engineering, Taishan University [2]School of Chemistry and Chemical Engineering,Shandong University [3]Scientific Research Department,Taishan University

出　　处：《Chinese Journal of Structural Chemistry》2013年第10期1449-1456,共8页结构化学（英文）

基　　金：supported by the National Natural Science Foundation of China(11174215);Natural Science Foundation of Shandong Province(ZR2012BL10 and ZR2010BL017);the University Science and Technology Project of Shandong Province(No.J13LD05);the Science and Technology Planning Project of Tai'an City(20102024)

摘　　要：The decarboxylation of pyrrole-2-carboxylic acid in acid solutions was elucidated by full optimization with the CPCM solvation model at the B3LYP/6-31 l＋＋G（d,p） level. Compared with the single-point energy calculation, CPCM full optimization is better to model solvent environments to gain reasonable reaction mechanisms. The π interactions play a significant role in the decarboxylation of pyrrole-2-carboxylic acid （R）. Firstly, the a hydrogen is protonated, but all of the carbonyl hydration pathways bear relatively higher energy barriers. The carbonyl group can rove over the pyrrole ring, but it does not lead to the speciation of pyrrole and protonated carbon dioxide for the latter is an energy-rich species. The decarboxylation mechanism proposed here is that, the protonated pyrrole-2-carboxylic acid （RH） decarboxylates via direct C-C bond cleavage with the aid of a water molecule to accommodate the proton on the carbonyl group.The decarboxylation of pyrrole-2-carboxylic acid in acid solutions was elucidated by full optimization with the CPCM solvation model at the B3LYP/6-31 l＋＋G（d,p） level. Compared with the single-point energy calculation, CPCM full optimization is better to model solvent environments to gain reasonable reaction mechanisms. The π interactions play a significant role in the decarboxylation of pyrrole-2-carboxylic acid （R）. Firstly, the a hydrogen is protonated, but all of the carbonyl hydration pathways bear relatively higher energy barriers. The carbonyl group can rove over the pyrrole ring, but it does not lead to the speciation of pyrrole and protonated carbon dioxide for the latter is an energy-rich species. The decarboxylation mechanism proposed here is that, the protonated pyrrole-2-carboxylic acid （RH） decarboxylates via direct C-C bond cleavage with the aid of a water molecule to accommodate the proton on the carbonyl group.

关 键 词：DECARBOXYLATION reaction mechanism pyrrole-2-carboxylic acid B3LYP 

分 类 号：O643.1[理学—物理化学]