Peculiar structure of the HOOO(-) anion

Quantum chemical study of reaction mechanism between plutonium and nitrogen

The study of the reaction between plutonium and nitrogen is helpful in further understanding the interaction between plutonium and air molecules. Currently, there is no research on the microscopic reaction mechanism of plutonium nitridation reactions. Therefore, the microscopic mechanism of the Pu with N₂ gas phase reaction is explored in this study, based on density functional theory (DFT) using different basis functions. In this paper, the geometry of stationary points on the potential energy surface is optimized. In addition, the transition states are verified by frequency analysis and intrinsic reaction coordination (IRC). Finally, we obtained the reaction potential energy curve and micro reaction pathways. Analysis of the reaction mechanism shows that the reaction of Pu with N₂ has two pathways. Pathway 1 (Pu + N₂ → R1 → TS1 → PuN₂) has a T-shaped transition state and pathway 2 (Pu + N₂ → R2 → TS2 → PuN + N) has an L-shaped transition state. Both transition states have only one imaginary frequency. According to the comparison of the energy at each stagnation point along the two pathways, and the heat energy emitted by the two reaction paths, we found that pathway 1 is the main reaction pathway. The nature of Pu-N bonding evolution along the pathways was studied by atoms in molecules (AIM) and electron localization function (ELF) topological approaches. In order to analyze the role of the plutonium atom 5f orbital in the reaction, the variation in density state along the pathways was measured. Results show that the 5f orbital mainly contributes to the formation of Pu-N bonds, and the influence of temperature on the reaction rate is revealed by calculating the rate constants of the two reaction pathways.

An Evaluation of Gas Phase Enthalpies of Formation for Hydrogen-Oxygen (HxOy) Species

We have compiled gas phase enthalpies of formation for nine hydrogen-oxygen species (HxOy) and selected recommended values for H, O, OH, H2O, HO2, H2O2, O3, HO3, and H2O3. The compilation consists of values derived from experimental measurements, quantum chemical calculations, and prior evaluations. This work updates the recommended values in the NIST-JANAF (1985) and Gurvich et al. (1989) thermochemical tables for seven species. For two species, HO3 and H2O3 (important in atmospheric chemistry) and not found in prior thermochemical evaluations, we also provide supplementary data consisting of molecular geometries, vibrational frequencies, and torsional potentials which can be used to compute thermochemical functions. For all species, we also provide supplementary data consisting of zero point energies, vibrational frequencies, and ion reaction energetics.

Is HO3− multiple-minimum and floppy? Covalent to van der Waals isomerization and bond rupture of a peculiar anion

The HO₃⁻ anion is multiple-minimum and floppy: the two main isomers and isomerization barrier all lie quite below dissociation.

The Oxygen-Rich Carboxide Series: COn (n = 3, 4, 5, 6, 7, or 8)

The lowest-energy isomers of the high-order carboxide series, COn (n = 3-8), have been elucidated via ab initio quantum chemical calculations. The structures of the lowest order of these (3 and 4) are in close agreement with previous calculations and with experimental data. The structures of the higher-order species are elucidated and correlated to the previous structures, showing similarities in structure and reactivity pathways. The reaction energies of the formation of all products are shown to be related. Exothermic pathways of formation often involve a C2v form of CO2, which was shown to be metastable. The newly identified species could be intermediates in atmospheric reactions. The calculated vibrational frequencies and IR intensities may be used to identify these metastable species.

Hemiortho Esters and Hydrotrioxides as the Primary Products in the Low-Temperature Ozonation of Cyclic Acetals: An Experimental and Theoretical Investigation

Low-temperature ozonation (-78 degrees C) of 1,3-dioxolanes 1a-1f and 1,3-dioxanes 1g and h in acetone-d6, methyl acetate, and tert-butyl methyl ether produced both the corresponding hemiortho esters (2a-h, ROH) and acetal hydrotrioxides (3a-h, ROOOH) in molar ratios ROH/ROOOH ranging from 0.5 to 23. Both types of intermediates were fully characterized by 1H, 13C, and 17O NMR spectroscopy. DFT calculations suggest that ozone abstracts a hydride ion from 1 to form an ion pair, R+ -OOOH, which subsequently collapses to either the corresponding hemiortho ester (ROH) or the acetal hydrotrioxide (ROOOH). Hemiortho esters decomposed quantitatively into the corresponding hydroxy esters. Experimentally obtained activation parameters for the decomposition of 2a (E(a) = 13.5 +/- 1.0 kcal/mol, log A = 8.3 +/- 1.0) are in accord with a highly oriented transition state involving, according to B3LYP calculations (deltaH(a)(298) = 13.2 kcal/mol), two molecules of water as a bifunctional catalyst. This mechanism is also supported by the magnitude of the solvent isotope effect for the decomposition of 2e, i.e., k(H2O)/k(D2O) = 4.6 +/- 1.2. Besides the hydroxy esters and oxygen (3O2/1O2), dihydrogen trioxide (HOOOH) was formed in the decomposition of most of the acetal hydrotrioxides (ROOOH) investigated. The activation parameters for the decomposition of the hydrotrioxides 3a-e in various solvents were E(a) = 20 +/- 2 kcal/mol, log A = 13.5 +/- 1.5. Several mechanistic possibilities for the decomposition of ROOOH were tested by experiment and theory. The formation of the hydroxy esters and oxygen could be explained by the intramolecular transfer of the proton to form the hydroxy ester. The assistance of water in the decomposition of ROOOH to form the hydroxy esters, either directly or via hemiortho esters, was also investigated. According to DFT calculations, the formation of a hydroxy ester via hemiortho ester is energetically more favorable (deltaH(a)(298) = 14.5 kcal/mol), again due to the catalytic effect of two water molecules. HOOOH generation requires the involvement of water in the decomposition of ROOOH where the direct formation out of ROOOH is energetically preferred. The energy for a reaction between two molecules of water and singlet oxygen (delta1O2) is too high to occur in solution.

Hydrogen Isotope Effects and Mechanism of Aqueous Ozone and Peroxone Decompositions

Hydrogen peroxide exalts the reactivity of aqueous ozone by reasons that remain obscure. Should H2O2 enhance free radical production, as it is generally believed, a chain mechanism propagated by (.OH/.O2-) species would account for O3 decomposition rates in neat H2O, HR-O3, and in peroxone (O3 + H2O2) solutions, HPR-O3. We found, however, that: (1) the radical mechanism correctly predicts HR-O3 but vastly overestimates HPR-O3, (2) solvent deuteration experiments preclude radical products from the (O3 + HO2-) reaction. The modest kinetic isotope effect (KIE) we measure in H2O/D2O: HR-O3/DR-O3 = 1.5 +/- 0.3, is compatible with a chain process driven by electron- and/or O-atom transfer processes. But the large KIE found in peroxone: HPR-O3/DPR-O3 = 19.6 +/- 4.0, is due to an elementary (O3 + HO2-) reaction involving H-O2- bond cleavage. Since the KIE for the hypothetical H-atom transfer: O3 + HO2- HO3. +.O2-, would emerge as a KIE1/2 factor in the rates of the ensuing radical chain, the magnitude of the observed KIE must be associated with the hydride transfer reaction that yields a diamagnetic species: O3 + HO2- HO3- + O2. HO3-/H2O3 may be the bactericidal trioxide recently identified in the antibody-catalyzed addition of O2(1Deltag) to H2O.

The role of the HOOO(-) anion in the ozonation of alcohols: large differences in the gas-phase and in the solution-phase mechanism

The mechanism of the ozonation of isopropyl alcohol was investigated for the gas and the solution phase using second-order many body perturbation theory and density functional theory (DFT) with the hybrid functional B3LYP and a 6-311++G(3df,3pd) basis set. A careful analysis of calculated energies (considering thermochemical corrections, solvation energies, BSSE corrections, the self-interaction error of DFT, etc.) reveals that the gas-phase mechanism of the reaction is dominated by radical or biradical intermediates while the solution-phase mechanism is characterized by hydride transfer and the formation of an intermediate ion pair that includes the HOOO(-) anion. The product distribution observed for the ozonation in acetone solution can be explained on the basis of the properties of the HOOO(-) anion. General conclusions for the ozonation of alcohols and the toxicity of ozone (inhaled or administered into the blood) can be drawn.

Evidence for the HOOO(-) anion in the ozonation of 1,3-dioxolanes: hemiortho esters as the primary products

Low-temperature ozonation (-78 degrees C) of 2-methyl-1,3-dioxolane (1a) in acetone-d6, methyl acetate, and tert-butyl methyl ether produced both the corresponding acetal hydrotrioxide (3a, ROOOH) and the hemiortho ester (2a, ROH) in molar ratio 1:5. Both intermediates were fully characterized by 1H, 13C, and 17O NMR spectroscopy, and they both decomposed to the corresponding hydroxy ester at higher temperatures. The mechanism involving the HOOO- anion formed by the abstraction of the hydride ion by ozone to form an ion pair, R+ -OOOH, with its subsequent collapse to either the corresponding hemiortho ester (ROH) or the acetal hydrotrioxide (ROOOH) was proposed. This mechanism is supported by the PISA/B3LYP/6-311++G(3df,3pd) calculations.