Electron spin resonance study of x-irradiated single crystals of dimethyl sulfone

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Abstract
The ESR spectra of x‐irradiated single crystals of dimethyl sulfone, O2S(CH3)2 have been examined at temperatures from 77 to 353 K. Between 77–153 K the spectra are dominated by an isotropic quartet of lines of intensity ratio 1:3:3:1, centered at g=2.0026±0.0001, with a hyperfine interval of 20.9±0.2 G. This spectrum originates from a methyl radical formed by the breaking of an S–C bond. On warming, the intensity of the methyl quartet decreased markedly at 163 K, being replaced by a singlet signal after several irreversible radical conversions had taken place. This singlet, which was stable from 173 to 333 K, is characterized by g values 2.0022, 2.0061, and 2.0067±0.0001. No hyperfine structure was observed. This spectrum is attributed to the O2ṠCH3 radical. The g=2.0022 is oriented perpendicular to the –SO2 plane, as expected for an unpaired electron principally located in a 3p (π) orbital on the S atom. The other g values are symmetrically located with respect to the two S–O bonds and lie on the SO2 plane. This indicates that the remaining S–C bond, on warming, reorients itself into the SO2 plane. Observation of the 33S spectrum confirms this interpretation. Spin densities of the unpaired electron on the S atom are ρ3s=0.074 and ρ3p=0.33.