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

Abstract

The phenylperoxy radical 1 has been synthesized by the reaction of the phenyl radical 2 with (3)O(2). Radical 1 could be either generated in the gas phase and subsequently trapped in solid argon at 10 K, or directly synthesized in argon matrices. By reacting 2 as well as its perdeuterated isotopomer [D(5)]-2 with (16)O(2) and with (18)O(2), respectively, the four isotopomers [H(5)]-(16)O(2)-1, [D(5)]-(16)O(2)-1, [H(5)]-(18)O(2)-1, and [D(5)]-(18)O(2)-1 were matrix-isolated and characterized by IR spectroscopy. The experimental IR spectra are in excellent agreement with results from DFT calculations. Irradiation of 1 with visible light produces the 2-oxepinoxy radical 5 in a clean reaction. Subsequent irradiation results in ring-opening and formation of several conformers of ketoketene 6. The radicals 1, 5, and 6 play an important role in the combustion of aromatic hydrocarbons and could now be isolated and spectroscopically characterized for the first time.

The Benzylperoxyl Radical as a Source of Hydroxyl and Phenyl Radicals

“…Depending on the concentration of oxygen, radicals 5 and 7 are expected to be trapped by O 2 to give the corresponding peroxyl radicals, which undergo subsequent rearrangements. [30,31] The combustion of aromatic compounds is a highly complicated process, and the results presented herein can help to identify the major pathways.…”

Photochemistry and Reactivity of the Phenyl Radical–Water System: A Matrix Isolation and Computational Study

“…Annealing at 30 K, however, allows rapid diffusion of O 2 and the phenylperoxy radical is formed in a clean bimolecular reaction. [28] Doping argon matrices containing the products of the FVP of 2 with 0.1-1 % of H 2 O results in some significant changes in the IR spectra. Most notably are these changes in the area of the out-of-plane (o.o.p) CH deformation modes between 650 and 720 cm À1 (Figure 1).…”

“…This has been shown previously in the case of O 2 ‐doped argon matrices in which, at temperatures below 15 K, the diffusion of trapped molecules is very slow and no reaction between 1 and O 2 is observed. Annealing at 30 K, however, allows rapid diffusion of O 2 and the phenylperoxy radical is formed in a clean bimolecular reaction 28…”

Generation and characterization of the phenylthiyl radical and its oxidation to the phenylthiylperoxy and phenylsulfonyl radicals

“…3); in highly diluted matrices (0.1% of O 2 ), the monomers predominate. Annealing the matrices containing 1 and O 2 (0.1-1%) at temperatures above 30 K allows small trapped molecules to diffuse 50,51 and this results in an increase of bands of 4g. In addition, dilution experiments allowed us to differentiate dimers from higher aggregates.…”

“…51 The reaction of alkyl radicals with oxygen analogously results in the formation of alkylperoxy radicals, which usually proceed without or with very low barriers. [51][52][53] The fundamental question whether the formation of 4 by addition of molecular oxygen to 1 is an exothermic or endothermic process is not yet unambiguously answered by theory. The reported DE value computed at BHLYP/cc-pVTZ indicates a mildly exothermic process (À7.9 kcal mol À1 ) for the formation of 4.…”