title: Peculiar structure of the HOOO(-) anion.
abstract: The HOOO(-) anion (1) can adopt a triplet state (T-1) or a singlet state (S-1), where the former is 9.8 kcal/mol (DeltaH(298) = 10.3 kcal/mol) more stable than the latter. S-1 possesses a strong O-OOH bond with some double bond character and a weakly covalent OO-OH bond (1.80 A) according to CCSD(T)/6-311++G(3df,3pd) calculations (the longest O-O bond ever found for a peroxide). In aqueous solution, S-1 adopts a geometry closely related to that of HOOOH (OO(O), 1.388 A; (O)OO(H), 1.509 A; tau(OOOH), 78.3 degrees ), justifying that S-1 is considered the anion of HOOOH. Dissociation into HO anion and O(2)((1)Delta(g)) requires 15.4 (DeltaH(298) = 14.3; DeltaG(298) = 8.9) kcal/mol. Structure T-1 corresponds to a van der Waals complex between HO anion and O(2)((3)Sigma(g)(-)) having a binding energy of 2.7 (DeltaH(298) = 2.1) kcal/mol. Modes of generating S-1 in aqueous solution are discussed, and it is shown that S-1 represents an important intermediate in ozonation reactions.
authors.affiliation: Department of Theoretical Chemistry, University of Göteborg, Reutersgatan 2, S-41320, Göteborg, Sweden.
authors.forename: Elfi
authors.initials: E
authors.lastname: Kraka
authors.forename: Dieter
authors.initials: D
authors.lastname: Cremer
authors.forename: Joze
authors.initials: J
authors.lastname: Koller
authors.forename: Bozo
authors.initials: B
authors.lastname: Plesnicar
mesh_terms: D000838:Anions / Q000737:chemistry; D008958:Models, Molecular; D010084:Oxidation-Reduction; D010087:Oxides / Q000737:chemistry*; D010126:Ozone / Q000737:chemistry*; D012996:Solutions; D013055:Spectrophotometry, Infrared; D013816:Thermodynamics
chemical_list: D000838:Anions; D010087:Oxides; D012996:Solutions; D010126:Ozone