Computational characterization of sulfur-cxygen-bonded sulfuranyl radicals derived from alkyl- and (carboxyalkyl)thiopropionic acids: evidence for sigma-type radicals.
Sulfide radical cations are known to stabilize via sulfur-oxygen bond formation with carboxylic acid functions. However, structural information on the resulting sulfuranyl radicals has so far only been provided by ESR spectroscopy for more stable, aromatic-substituted species, while the rather short-lived aliphatic sulfuranyl radicals have largely been characterized by time-resolved UV spectroscopy only. Therefore, we have obtained theoretical structural information on S-O-bonded sulfuranyl radicals from three model compounds, tert-butyl 2-(methylthio)peroxybenzoate, 3-methylthiopropionic acid, and 3,3'-thiodipropionic acid, using density functional theory, semiempirical, and molecular mechanics methods. All S-O-bonded species exist predominantly as three-electron-bonded sigma-radicals with an estimated heterolytic bond dissociation energy of the S therefore O bond on the order of 23-27 kcal mol(-1). Characteristic optical absorption bands, vibrational frequencies, and hyperfine coupling tensors are evaluated to facilitate the identification of such radicals by time-resolved UV, IR, and ESR spectroscopy.
Pogocki
Dariusz
D
Department of Pharmaceutical Chemistry, University of Kansas, 2095 Constant Avenue, Lawrence, Kansas 66047, USA.
Schöneich
Christian
C
D000473:Alkanes / Q000737:chemistry*; D002384:Catalysis; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals; D007700:Kinetics; D008958:Models, Molecular; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D011422:Propionates / Q000737:chemistry*; D013055:Spectrophotometry, Infrared; D013056:Spectrophotometry, Ultraviolet; D013440:Sulfides / Q000737:chemistry; D013455:Sulfur / Q000737:chemistry*
D000473:Alkanes; D005609:Free Radicals; D011422:Propionates; D013440:Sulfides; D013455:Sulfur; D010100:Oxygen