Spectroscopic characterization and photochemistry of the vinylsulfinyl radical

Abstract

The simplest α,β-unsaturated sulfinyl radical CH₂C(H)SO˙ has been generated in the gas phase by high-vacuum flash pyrolysis (HVFP) of sulfoxide CH₂C(H)S(O)CF₃ at ca. 800 °C. Two planar cis and trans conformers of CH₂C(H)SO˙ were isolated in cryogenic matrixes (N₂, Ne, and Ar) and characterized with IR and UV/Vis spectroscopy. In addition to the photo-induced cis trans conformational interconversion, CH₂C(H)SO˙ displays complex photochemistry. Upon irradiation with a purple light LED (400 nm), CH₂C(H)SO˙ isomerizes to novel radicals CH₃SCO˙, ˙CH₂SC(O)H, and ˙CH₂C(O)SH with concomitant dissociation to a caged molecular complex CH₃S˙⋯CO. Subsequent UV-laser (266 nm) irradiation causes fragmentation to ˙CH₃/OCS and additional formation of an elusive carbonyl radical CH₃C(O)S˙, which rearranges to ˙CH₂C(O)SH upon further UV-light irradiation (365 nm). The vibrational data and bonding analysis of the two conformers of CH₂C(H)SO˙ suggest that both are floppy radicals in which the unpaired electron conjugates with the vicinal π(CC) bond, leading to significant contribution of the canonical resonance form of ˙CH₂–C(H)SO. The mechanism for the isomerization of CH₂C(H)SO˙ is discussed based on the observed intermediates along with a computed potential energy profile at the CCSD(T)-F12a/aug-cc-pVTZ//B3LYP/6-311++G(3df,3pd) level of theory.