The structures of the aggregates of the neutral and anionic forms of acetohydroxamic acid CH 3CONHOH (AH) with a water molecule have been calculated at the MP2(FC)/AUG-cc-pVDZ level of theory, for evaluating the effect of intermolecular hydrogen bonds formation on the deprotonation processes of AH. Considering the molecules to be isolated, the Z-amide is the most stable neutral form whereas the E-amide + H 2O system represents the most stable aggregate. In the system Z-amide + H 2O the intramolecular hydrogen bond is preserved. The theoretical results obtained clarify the interpretation of NMR studies in acetone solution (with residual water), as well as the kinetics of complex formation in aqueous solution between Ni(II) and hydroxamics acids investigated by spectrophotometric and stopped-flow techniques. In the gas phase, the Z-amide species and the less stable Z-imide form undergo deprotonation, giving rise to two stable anions. Upon deprotonation the E forms can produce three stable anions. The aim of this paper is to compare ab initio calculations performed in solution using two different approaches where the solvent is treated as a continuum of constant permittivity. Two different solvents are studied: acetone and water. The calculated solvation energies in water with the PCM model directly applied on the isolated species are compared to those determined building the molecular aggregates with one water molecule. In all cases studied, the N-deprotonation of the Z-amide is the most probable process. Since more than one deprotonation process has been experimentally observed, the relative probabilities of the O-deprotonation of the Z-amide, and the N- and O-deprotonation of the E-amide forms are discussed. The probability of N-deprotonation from the Z-amide form increases in acetone.