Unimolecular Decomposition of the 2-Oxepinoxy Radical:  A Key Seven-Membered Ring Intermediate in the Thermal Oxidation of Benzene

Abstract

The Gibbs free energy profiles for the unimolecular decomposition of the 2-oxepinoxy radical at temperatures ranging from 298 to 1250 K have been obtained using the B3LYP method. Intermediates and transition states have been obtained that link the 2-oxepinoxy radical to various products that have been experimentally observed during the thermal oxidation of benzene. The pathways explored include the rearrangement of 2-oxepinoxy radical to cyclopentadienyl radical, pyranyl radical, and various C4, C3, and C2 compounds. The decomposition of 2-oxepinoxy radical for these pathways provides a mechanism that proceeds from C6 → C5 → C4 → C2 intermediates but does not include the cyclopentadienyl radical as a required intermediate. The most viable pathway at temperatures between 1000 and 1250 K yields either the 5-oxo-2-cyclopenten-1-yl radical and CO or the vinyl radical, acetylene, and two molecules of CO as products. A mechanism to form 5-oxo-2-cyclopenten-1-yl, a possible precursor to cyclopentadienone, is compared to the pathway for cyclopentadienone formation from the decomposition of phenoxy radical to cyclopentadienyl radical and then subsequent oxidation and rearrangement.

Thermodynamic properties of the species resulting from the phenyl radical with O2 reaction system

“…Most of the enthalpies of formation that we have calculated from the supplemental information by Hadad et al 15 are in agreement with the B3LYP, G3, and G3MP2B3 values reported across in Table III. There are, however, a few exceptions: as an example, a deviation of about 8 kcal mol −1 is observed for Y(C5)OC • DO, Y(C5O)C • DO, and p ‐ODY(C6)O • while the enthalpy data by Lin et al show agreement with our calculated G3 values.…”

The influence of electron donor and electron acceptor groups on the electronic structure of the anti‐inflammatory tripeptide Cys‐Asn‐Ser

“…Single-point calculations were performed on optimized structures (neutral, anionic, and cationic) at DFT (B3LYP) levels with a 6-311þG(2d,2p) basis set. In all cases, we have verified that our DFT calculations produce negligible spin contamination, which is in agreement with other results reported in the literature [19,20]. To determine serine (Ser) amino acid relative acidity, deprotonation energy (DE) was calculated by deprotonating the H2 hydrogen atom, respectively (see Fig.…”

Matrix Isolation and Spectroscopic Characterization of the Phenylperoxy Radical and Its Rearranged Products

“…However, since the IR spectra calculated for various geometrical isomers of 6 are very similar, an assignment to one of the isomers was not possible. In a study by Fadden and Hadad for the ring-opening of 5 to ketoketene 6 a thermal activation barrier of 23.4 kcal mol À1 was calculated, [23] while two other rearrangements of 5 were found to proceed via considerably higher activation barriers. Our experiments do not allow us to determine if the ring-opening is a photochemical or a hot ground state reaction.…”