Two hitherto unreported sulfur-centered radicals CF SO and CF OS were generated in the gas phase through high-vacuum flash pyrolyses of sulfoxide CF S(O)X (X=CF , Cl, PhO) precursors. The CF OS molecule is the first experimental example that constitutes an oxathiyl radical. It was isolated and characterized by combining matrix-isolation IR and UV/Vis spectroscopy with quantum chemical computations up to the UCCSD(T)-F12/cc-pVTZ-F12 level of theory. Upon UV light irradiation (254 or 266 nm), sulfinyl radical (CF SO ) isomerizes to oxathiyl radical (CF OS ) in cryogenic noble gas matrices (Ar and Ne). Natural population analyses at the BP86/def2-TZVPP//UCCSD(T)-F12/cc-pVTZ-F12 level suggest that the spin density in CF OS is mainly localized on the sulfur atom (0.86), whereas, in CF SO the spin density is almost equally distributed on the sulfur (0.55) and oxygen (0.43) atoms.

The parent thioketene S-oxide H CCSO has been generated in the gas phase through flash vacuum pyrolysis (ca. 1000 K) of vinyl sulfoxide H CC(Br)-S(O)CF via the intermediacy of a novel vinyl sulfinyl radical H C=C(Br)-SO (syn and anti conformers). Upon irradiation at 266 nm, H CCSO decomposes into HCCH/SO and H CS/CO in cryogenic Ar matrix. Whereas, visible-light irradiations result in syn↔anti conformational interconversion in H C=C(Br)-SO. The molecular structures of H CCSO and isomers are computationally studied at the CCSD(T)-F12/VTZ-F12 level of theory, and the bonding properties of H CCSO are analyzed with the EDA-NOCV method at the M06-2X/TZ2P level.

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