Three symmetric intramolecular proton exchanges involving oxygen atoms in negatively charged systems have been studied by ab initio methods. An important rearrangement of the electronic charge density takes place as the reactions proceed. The O–O bond is broken in the hydroperoxide anion at the transition state, the energy barrier being very large. In the water–hydroperoxide anion complex the water molecule acts as a bifunctional catalyst, the O–O bond remaining formed and the energy barrier being significantly lowered. Finally, the proton transfer in the glycolate anion occurs through a C2v transition state whose total electronic charge density presents a ring point, the energy barrier being very small. © 1990, American Chemical Society. All rights reserved.