Abstract: Sodium borohydride has been widely used in different organic reductions due to its moderate chemical activity. The reductions of ester with sodium borohydride could produce various alcohols as intermediates for further reactions. The esters with different alkyl substituents are used as the models in sodium borohydride reductions, and on-set temperatures, half-life periods and transition state(TS) energies were obtained experimentally. Some of the TS energetics were computed using B3LYP/6-31++G(d,p)//HF/6-31G(d,p) method. The differences of on-set temperatures among these esters were substantial and some observed selectivities were obtained when the aliphatic substituents changed from Me, Et, n-Pr to n-Bu. Odd-even carbon effect, which was first mentioned in our previous report in enantioselective additions of diethylzinc to benzaldehyde, was observed again in the reductions. Traditionally, organic theory uses the size of the substitutents to explain the reaction TS energy order. However, the traditional theory can not be used to explain the observed odd-even carbon effect. The reason for this effect happened in different reactions is still unknown. Furthermore, the effect of solvent in the reductions was investigated primarily.

Key words: Aliphatic esters, Chemoselective reduction, Transition state energy, Half-life period, Odd-even carbon effect