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