Abstract The Birch reduction converts aromatic compounds possessing a benzenoid ring into products derived from 1,4-cyclohexadienes, which has rarely been explicitly concluded in various organic chemistry textbooks. Current mechanisms indicate that the step determining the position of the carbon-carbon double bonds in the product is the protonation of the anion intermediate after capturing two electrons. This article studied the regional selectivity in the protonation step on the base of quantum chemical calculations and reports of other literature. The results demonstrate both qualitatively and quantitatively that the protonation site is mainly the carbon atom with the largest orbital coefficient in the intermediate's HOMO, which means the regional selectivity is resulted from chemical kinetics factors.
