First EPR spectroscopic detection of photochemically generated carbonyloxyl radicals in solution under steady-state conditions

Peer reviewed: YesNRC publication: Ye

Further spectroscopic and kinetic studies on carbonyloxyl radicals

UV-visible absorption spectra and kinetic data obtained at room temperature are reported for three (alkenylcarbonyl)oxyls: trans-(CH 3) 3CCH=CHC(O)O \u2022, 1a; trans-C 6H 5CH=CHC(O)O \u2022, 1b; (CH 3) 2C=CHC(O)O \u2022, 1c; and two (alkynylcarbonyl)oxyls: (CH 3) 3CC 61CC(O)O \u2022, 2a; C 6H 5C 61CC(O)O \u2022, 2b. Rate constants for decarboxylation of 1a, 1b, 2a, and 2b are estimated to be 641.1 7 10 7, 1 7 10 6, 5 7 10 5 and 2 7 10 5 s -1, respectively. The first-order decay of 1c would appear to occur primarily by an intramolecular H atom abstraction, k 3c (2 \ub1 1) 7 10 7 s -1. The (alkynylcarbonyl)oxyls are more reactive than the (alkenylcarbonyl)oxyls in a variety of H atom abstraction reactions, e.g., with c-C 6H 12, and addition reactions, e.g., with C 6H 5CH=CH 2. Combining the present and earlier 5-7 kinetic data for carbonyloxyls yields the following order of decreasing reactivity for hydrogen abstraction and addition reactions: RC 61CC(O)O \u2022 65 ROC(O)O \u2022 > RR\u2032C=CHC(O)O \u2022 65 C 6H 5C(O)O \u2022. The reactivities of meta- and para-substituted aroyloxyls can be correlated with the intrinsic acidities and with the pK a's of the corresponding benzoic acids, reactivity increasing with acid strength.Peer reviewed: YesNRC publication: Ye

Matrix isolation EPR study of novel radical cations from bicyclic[3.2.0] and monocyclic C7H8 and C7H10 compounds

The radical cations of bicyclo[3.2.0]hepta-2,6-diene and bicyclo[3.2.0]hept-2-ene have been obtained by γ-irradiation of the parent compounds in Freon matrices and their structures investigated by EPR spectroscopy and MNDO and INDO calculations. In a CFCl3 matrix, ring opening to the isomeric cycloheptatriene and cycloheptadiene radical cations occurred, whereas in a CF2ClCFCl2 matrix the prevalent reaction was deprotonation to the neutral bicyclo[3.2.0]hepta-2,6-dien-4-yl and bicyclo[3.2.0]hept-2-en-4-yl radicals, respectively