Quantitative Structure−Stability Relationships for Oxides and Peroxides of Potential Atmospheric Significance

Abstract

A critical analysis of the most recent experimental and ab initio thermochemical data on gas-phase species reveals that (1) isodesmic metathetical reactions among simple oxides, 1/2 XOX + 1/2 YOY ↔ XOY, and those exclusively involving peroxides 1/2 XOOX + 1/2 YOOY ↔ XOOY, are nearly thermoneutral (ΔH_r = 0 ± 3 kcal/mol), but exchange reactions between oxides and peroxides, XOX + YOOY ↔ YOY + XOOX, are generally not, (2) bond additivity values BAV[X−(O−O)−X]'s for the contributions of the peroxide bond to the heats of formation of H-, C-, N-, S-, F-, and Cl-containing peroxides decrease linearly with Pauling electronegativities χ(X)'s and (3) semiempirically evaluated (MOPAC) thermochemical datasets, even when inaccurate in absolute terms, are internally consistent with such rules. These findings happen to provide the basis for the rapid and systematic assessment of the stability of novel oxides and peroxides. In this paper, that focuses on species that could be formed in the terrestrial atmosphere, we briefly discuss XOO−H bond energy trends in hydroperoxides, the existence of stable and metastable peroxy XOO• radicals, the thermochemistry of peroxyacyl nitrates, of Br- and S-containing peroxides, and the mechanism of the (FO + ClO), (FO + NO_2), (OH + OClO), (HO_2 + ClO), (ClO + NO_2), and (ClO + NO_3) reactions, among other issues.