Further Spectroscopic and Kinetik Studies on Carbonyloxyl Radicals

Article abstract of DOI:10.1021/jo00007a029

UV-visible absorption spectra and kinetic data obtained at room temperature are reported for three (alkenylcarbonyl)oxyls: trans-(CH3)3CCH=CHC(O)O^., 1a; trans-C6H5CH=CHC(O)O^., 1b; (CH3)2C=CHC(O)O^., 1c; and two (alkynylcarbonyl)oxyls: (CH3)3CC<*>CC(O)O^., 2a; C6H5C<*>CC(O)O^., 2b.Rate constants for decarboxylation of 1a, 1b, 2a, and 2b are estimated to be 7, 1 x 10⁶, 5 x 10⁵ and 2 x 10⁵ s^-1, respectively.The first-order decay of 1c would appear to occur primarily by an intramolecular H atom abstraction, k ca. (2 +/- 1) x 10⁷ s^-1.The (alkynylcarbonyl)oxyls are more reactive than the (alkenylcarbonyl)oxyls in a variety of H atom abstraction reactions, e.g., with c-C6H12, and addition reactions, e.g., with C6H5CH=CH2.Combining the present and earlier 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^. >/= C6H5C(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.