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 (3 df, 3 pd) level. The activation energy (E-a1 = E-TS1 - E-Re) of the rate-controlling step obtained at B3LYP/6-311 + +G (3 df, 3pd). level was 189. 5kJ . mol(-1), which is closely correlated with the available experimental data (180. 3 +/- 3. 4) kJ . mol(-1). The relative error is 5.08%.