Quantum chemistry is applied to the study of condensation mechanism of the reaction between propionate acid and polyethylene polyamine. It is found that the activation energy is increased remarkably by acid catalyst. Nucleophilic addition and elimination are considered as the key steps of this reaction, and the rate of reaction is determined by the latter. By using AM1 method, equilibrium geometries, net charges and the potential curves of the reaction are obtained. The activation energies calculated for the nucleophilic addition and elimination are 6.258kJ/mol and 206.15kJ/mol respectively. The results indicate that protonation of O(3) atom lead to an increase of charge on C(2), N(12) and smaller gap between the HOMO and LUMO. This suggests the interaction between the frontier orbitals is enhnced by protonation. In this case, acid catalyst plays an important role in the reaction.

Key words: AMIDES P, PROPIONIC ACID, CONDENSATION REACTION, REACTION MECHANISM, ACTIVATION ENERGY, GEOMETRICAL ISOMERISM, ELECTRONIC STRUCTURE