Theoretical insights into the reaction mechanisms between 2,3,7,8-tetrachlorodibenzofuran and the methylidyne radical

Theoretical study on the reaction between silacyclopropenylidene and three-membered heterocyclic compounds (azirane and oxirane): An alternative approach to the formation of heterocyclic silylene

The reaction mechanism between silacyclopropenylidene and three-membered heterocyclic compounds (azirane and oxirane) has been systematically investigated at the B3LYP/6-311+G* level of theory in order to better understand the reactivity of unsaturated cyclic silylene. Geometry optimizations and vibrational analyses have been conducted for the stationary points on the potential energy surface of the system. Calculations show that the Si-spiroheterocyclic intermediate and four-membered heterocyclic silylene compound could be produced through the insertion process and subsequent dissociation process between silacyclopropenylidene and three-membered heterocyclic compounds. For the insertion process, it is easier for silacyclopropenylidene to insert into C-N bond of azirane than into C-O bond of oxirane. This study is helpful to understand the reactivity of silacyclopropenylidene, the evolution of silicon-bearing molecules in space, and to offer an alternative approach to the formation of enlarged heterocyclic silylene compound.

Theoretical Insights into the Reaction Mechanism between 2,3,7,8-Tetrachlorodibenzofuran and Hydrogen Peroxide: A DFT Study

A detailed knowledge of the reactivity of 2,3,7,8-tetrachlorodibenzofuran (TCDF) at the molecular level is important to better understand the transformation of dioxins analogous to TCDF in the environment. To clarify the reactivity of the organic hydroperoxides toward TCDF, the reaction of the TCDF with hydrogen peroxide (H2O2) and its anion has been investigated theoretically. For the reaction of the neutral H2O2, a molecular complex can be formed between TCDF and H2O2 first. Then, the nucleophilic aromatic substitution of TCDF by H2O2 occurs in the presence of the water molecules to form an intermediate containing an O-O bond. Finally, the O-O bond cleavages homolytically for the above intermediate. On the other hand, as for the reaction of the anion of H2O2 (HO2 -), the nucleophilic addition of HO2 - to TCDF can also occur besides the nucleophilic aromatic substitution reaction mentioned above, resulting in the dissociation of the C-O bond of TCDF. Unlike the reaction involving neutral H2O2, no water molecules are required. In addition, the selected substitution effects, such as F-, Br-, and CH3-substituents, on the reactivity of the above reaction have also been explored. Hopefully, the present results can enable us to gain insights into the reactivity of the organic hydroperoxides with TCDF-like environmental pollutants.

Theoretical Investigations on the Reactivity of Hydrogen Peroxide toward 2,3,7,8-Tetrachlorodibenzo-p-dioxin

Acquiring full knowledge of the reactivity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is crucial for the better understanding of the transformation and degradation of TCDD-like dioxins in the environment. To clarify the reactivity of the organic hydroperoxides toward TCDD, in this study, the reactions between the neutral/anion of the hydrogen peroxide (H₂O₂) and TCDD have been systematically investigated theoretically. It was found that the neutral H₂O₂ is relatively difficult to react with TCDD compared with its anion, exhibiting the pH dependence of the title reaction. As for the anion of H₂O₂, it reacts with TCDD through two reaction mechanisms, i.e., nucleophilic substitution and nucleophilic addition. For the former, the terminal O atom of HO₂- nucleophilically attacks the C atom of the C-Cl bond in TCDD to form an intermediate containing an O-O bond, accompanying the dissociation of the chlorine atom. For the latter, the terminal O atom of HO₂- can be easily attached to the C atom of the C-O bond in TCDD, resulting in the decomposition of C-O bond and the formation of an intermediate containing an O-O bond. For these formed intermediates in both reaction mechanisms, their O-O bonds can be homolytically cleaved to produce different radicals. In addition, the selected substitution effects including F-, Br-, and CH₃- substituents on the above reactions have also been studied. Hopefully, the present results can provide new insights into the reactivity of the organic hydroperoxides toward TCDD-like environmental pollutants.

Theoretical Investigations on the Reactivity of Methylidyne Radical toward 2,3,7,8-Tetrachlorodibenzo-p-Dioxin: A DFT and Molecular Dynamics Study

To explore the potential reactivity of the methylidyne radical (CH) toward 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the reaction mechanism between them has been systematically investigated employing the density functional theory (DFT) and ab initio molecular dynamics simulations. The relevant thermodynamic and kinetic parameters in the possible reaction pathways have been discussed as well as the IR spectra and hyperfine coupling constants (hfcc's) of the major products. Different from the reaction of the CH radical with 2,3,7,8-tetrachlorodibenzofuran, CH radical can attack all the C-C bonds of TCDD to form an initial intermediate barrierlessly via the cycloaddition mechanism. After then, the introduced C-H bond can be further inserted into the C-C bond of TCDD, resulting in the formation of a seven-membered ring structure. The whole reactions are favorable thermodynamically and kinetically. Moreover, the major products have been verified by ab initio molecular dynamics simulations. The distinct IR spectra and hyperfine coupling constants of the major products can provide some help for their experimental detection and identification. In addition, the reactivity of the CH radical toward the F- and Br-substituted TCDDs has also been investigated. Hopefully, the present findings can provide new insights into the reactivity of the CH radical in the transformation of TCDD-like dioxins.

Theoretical Insights into the Interaction Mechanisms between Nitric Acid and Nitrous Oxide Initiated by an Excess Electron

Nitric acid (HNO₃) and nitrous oxide (N₂O) play an important role in the atmospheric chemistry in regulating the global environment and climate changes. In this study, the interaction mechanisms between them have been systematically investigated before and after the electron capture employing the density functional theory in combination with the AIM, NBO, and ab initio molecular dynamics calculations. It was found that HNO₃ and N₂O can form transient complexes through intermolecular H-bonds. HNNO, OH, and NO₂ free radicals can be produced after the electron capture of the formed complexes, providing an alternative source of these radicals in the atmosphere. The present results not only can provide new insights into the transformation of the HNO₃ and N₂O atmospheric species but also can enable us to better understand the potential role of the free electron in the atmosphere.