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Abstract: The formation of bimolecular complexes of HOOOH and the HOOO radical with sulfuric acid (H2SO4–HOOOH, H2SO4–HOOO ) has been investigated by using DFT (B3LYP/6-311++G(3df,3pd)) and CCSD(T)-F12 methods. For the first time the structures and the binding energies (BEs) for the various isomeric hydrogen-bonded complexes have been reported. The results reveal an unusually stable H2SO4–HOOOH eight-membered ring structure with two relatively strong hydrogen bonds, and with a calculated BE (CCSD(T)-F12) of 12.7kcalmol−1. This is equivalent to the BE in the H2SO4–HOOH complex investigated at the same theoretical level. The complexation of HOOO with H2SO4 stabilizes this metastable polyoxide intermediate by about 10.0kcalmol−1. [Copyright &y& Elsevier]

We demonstrate in this work by theory and experiment that benzaldehyde hydrotrioxide (PhC(O)OOOH), the intermediate most likely formed in the low-temperature ozonation of benzaldehyde, is too unstable to be detected by NMR (1H, 13C, and 17O) spectroscopy in various organic solvents at temperatures ⩾ -80 °C and that its previous detection must have been erroneous. Several plausible mechanisms for the formation of this polyoxide were explored by using density functional theory. We found that the formation of the hydrotrioxide involves the facile 1,3-dipolar insertion of ozone into the C-H bond (ΔH 11.1 kcal/mol) in a strongly exothermic process (ΔHR = -57.0 kcal/mol). The hydrotrioxide then quickly decomposes in a second concerted, exothermic reaction involving an intramolecular H transfer to form benzoic acid and singlet oxygen (O2(1Δg)) (ΔH = 5.6 kcal/mol), ΔHR = -14.0 kcal/mol). The equilibrium is thus expected to be shifted toward the products; therefore, this intermediate cannot be observed experimentally. Peroxybenzoic acid, still another major reaction product formed in the ozonation reaction, is formed as a result of the surprising instability of the RC(O)O-OOH bond (ΔHR = 23.5 kcal/mol), generating HOO and benzoyloxyl radicals. Both of these radicals can then initiate the chain autoxidation reaction sequence-the abstraction of a H atom from benzaldehyde to form either a benzoyl radical and HOOH or a benzoyl radical and benzoic acid. Because only very small amounts of HOOH were detected in the decomposition mixtures, the recombination of the benzoyl radical with the HOO radical (ΔHR = -80.7 kcal/mol) appears to be the major source of peroxybenzoic acid. A theoretical investigation of the mechanistic possibility of the involvement of still another intermediate, a cyclic tetraoxide (tetraoxolane) formed as a primary product in the 1,3-dipolar cycloaddition of ozone to the carbonyl. group of the aldehyde, revealed that the tetraoxide is a "real" molecular entity with the five-membered ring adopting an envelope conformation. The tetraoxide is destabilized by 7.0 kcal/mol relative to the reactant complex, and the transition state for its formation is 17.4 kcal/mol above the reactant complex, which, although accessible under the reaction conditions, is not expected to be competitive with the reaction generating the hydrotrioxide. [ABSTRACT FROM AUTHOR]

Abstraction of the iodine atom from aryl iodides by alkyl radicals takes place in some cases very efficiently despite the unfavorable difference in bond dissociation energies of CI bonds in alkyl and aryl iodides. The abstraction is most efficient in iodobenzenes, ortho-substituted with bulky groups. The ease of abstraction can be explained by the release of steric strain during the elimination of the iodine atom. The rate of abstraction correlates fairly well with the strain energy, calculated by density functional theory (DFT) and Hartree-Fock (HF) methods as a difference in the total energy of ortho and para isomers. However, besides the steric bulk, the presence of some other functional groups in an ortho substituent also influences the rate. The stabilization of the transition state, resembling a 9-I-2 iodanyl radical, by electron-withdrawing groups seems to explain a positive sign of the Hammett p value in the radical abstraction of halogen atoms. [ABSTRACT FROM AUTHOR]