title: Structural effects on the C-S bond cleavage in aryl tert-butyl sulfoxide radical cations.
abstract: The oxidation of a series of aryl tert-butyl sulfoxides (4-X-C6H4SOC(CH3)3: 1, X = OCH3; 2, X = CH3; 3, X = H; 4, X = Br) photosensitized by 3-cyano-N-methylquinolinium perchlorate (3-CN-NMQ(+)) has been investigated by steady-state irradiation and nanosecond laser flash photolysis (LFP) under nitrogen in MeCN. Products deriving from the C-S bond cleavage in the radical cations 1(+•)-4(+•) have been observed in the steady-state photolysis experiments. By laser irradiation, the formation of 3-CN-NMQ(•) (λ(max) = 390 nm) and 1(+•)-4(+•) (λ(max) = 500-620 nm) was observed. A first-order decay of the sulfoxide radical cations, attributable to C-S bond cleavage, was observed with fragmentation rate constants (k(f)) that decrease by increasing the electron donating power of the arylsulfinyl substituent from 1.8 × 10(6) s(-1) (4(+•)) to 2.3 × 10(5) s(-1) (1(+•)). DFT calculations showed that a significant fraction of the charge is delocalized in the tert-butyl group of the radical cations, thus explaining the small substituent effect on the C-S bond cleavage rate constants. Via application of the Marcus equation to the kinetic data, a very large value for the reorganization energy (λ = 62 kcal mol(-1)) has been calculated for the C-S bond scission reaction in 1(+•)-4(+•).
authors.affiliation: Dipartimento di Chimica and Istituto CNR di Metodologie Chimiche, Sezione Meccanismi di Reazione c/o Dipartimento di Chimica, Sapienza Università di Roma, P.le A. Moro 5, 00185 Rome, Italy.
authors.forename: Tullio
authors.initials: T
authors.lastname: Cavattoni
authors.forename: Tiziana
authors.initials: T
authors.lastname: Del Giacco
authors.forename: Osvaldo
authors.initials: O
authors.lastname: Lanzalunga
authors.forename: Marco
authors.initials: M
authors.lastname: Mazzonna
authors.forename: Paolo
authors.initials: P
authors.lastname: Mencarelli
mesh_terms: D002412:Cations / Q000737:chemistry; D005609:Free Radicals / Q000737:chemistry; D015394:Molecular Structure; D010084:Oxidation-Reduction; D011789:Quantum Theory; D013454:Sulfoxides / Q000737:chemistry*
chemical_list: D002412:Cations; D005609:Free Radicals; D013454:Sulfoxides