Abstract: 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％.

Key words: 2-bromopropionic acid, Gas-phase elimination, Density functional theory(DFT), Reaction mechanism