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 ) 3 CCH=CHC(O)O • , 1a; trans-C 6 H 5 CH=CHC(O)O • , 1b; (CH 3 ) 2 C=CHCH(O)O • , 1c; and two (alkynylcarbonyl)oxyls: (CH 3 ) 3 CC≡CC(O)O • , 2a; C 6 H 5 C≡CC(O)O • , 2b. The (alkynylcarbonyl)oxyls are more reactive than the (alkenylcarbonyl)oxyls in a variety of H atom abstraction reactions, e.g., with c-C 6 H 12 , and addition reactions, e.g., with C 6 H 5 CH=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≡CC(O)O • ≥ROC(O)O • >RR'C=CHC(O)O • ≥C 6 H 5 C(O)O • . 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