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

Abstract

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 $\pi$ 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 $\pi$ 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.