2-溴丙酸气相热消除反应的机理

用密度泛函（DFT）方法,在B3LYP/6-31G**水平上对2-溴丙酸气相消除反应机理进行了研究.计算表明,反应主要是通过半极化五元环结构过渡态进行的,羧基上的氢原子协助溴原子离去,羧基氧原子帮助稳定过渡态.在B3LYP/6-311＋＋G(3df,3pd)水平上对B3LYP/6-31G**优化的几何构型进行了单点能计算,计算所得反应的速度控制步骤的活化能为189.461 kJ•mol－1,偏离实验值((180.3±3.4) kJ•mol－1)5.08％.

Reaction Mechanism of the Gas-phase Elimination of 2-bromopropionic Acid

The gas-phase elimination of 2-bromopropionic acid was investigated using density functional theory (DFT) method. Molecular structures were calculated at the B3LYP/6-31G** level. The results obtained show that the gas-phase elimination of 2-bromopropionic acid proceeds via a semi-polar five-membered cyclic transition state, where the acidic H of the group COOH assisted the leaving Br atom, and the carboxylic oxygen stabilized this transition state. The single-point energies of all optimized molecular structures by B3LYP/6-31G** were counted at B3LYP/6-311＋＋G (3df,3pd) level. The activation energy(Ea1=ETS1－ERe)of the rate-controlling step obtained at B3LYP/6-311＋＋G (3df,3pd) level was 189.5 kJ•mol－1,which is closely correlated with the available experimental data(180.3±3.4) kJ•mol－1.The relative error is 5.08％.