Paramagnetic Resonance Study of Liquids during Photolysis. X. Hyperfine Interactions from 13C

Hyperfine splittings due to 13C in natural abundance have been observed in several short-lived radicals produced photolytically in liquids. Signal averaging was used for the weaker spectra. A radical made from acetate ion, ĊH2COO−, has carbon couplings of 32.09 and 13.85 G assigned to the ĊH2 and COO− carbons, respectively. Linewidth effects were seen. These results are discussed, and it is concluded that the species is a planar π radical. The coupling for the methyl carbons of (CH3)2ĊOH is 5.35 G, and that for the central carbon is 65.05 G. It is concluded that the radical skeleton is not planar; the species is not a pure π radical. A coupling of 11.05 G found in CH3COCH2NO2·− is assigned to the carbonyl carbon, and the results are described in terms of a β-coupling model. The acetoin radical, CH3̇COHCOCH3, in strongly acid media undergoes rapid dynamic exchange. The two central carbons become equivalent and the 13C coupling is 5.12 G. In the absence of acid, all carbons of the radical are inequivalent. Satellites due to 13C were seen, and one coupling of 7.8 G was evaluated. A provisional coupling for another carbon was assigned.