Comparison between intramolecular proton transfers involving the carboxylate and alkoxide groups

We have studied the intramolecular proton transfer in the hydroxyacetate, hydrogenoxalate and glycolate anions by means of ab initio calculations. Due to the higher proton affinity of RO- as compared to R-COO-, there is only one minimum in the hydroxyacetate potential surface. Conversely, given that hydrogenoxalate and glycolate anions are symmetric systems, a transition state appears in both cases. The greater barrier in the hydrogenoxalate with respect to the glycolate anion can be attributed to the reorganisation energy of the substrate. The proton motion in the hydrogenoxalate molecule is clearly coupled to the motion of the other atoms. © 1990.