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Structural effects on the C-S bond cleavage in aryl tert-butyl sulfoxide radical cations (Articolo in rivista)

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Structural effects on the C-S bond cleavage in aryl tert-butyl sulfoxide radical cations (Articolo in rivista) (literal)

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T. Cavattoni, T. Del Giacco, O. Lanzalunga, M. Mazzonna, P. Mencarelli (2013)
Structural effects on the C-S bond cleavage in aryl tert-butyl sulfoxide radical cations
in Journal of organic chemistry; ACS, American chemical society, Washington, DC (Stati Uniti d'America)
(literal)

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T. Cavattoni, T. Del Giacco, O. Lanzalunga, M. Mazzonna, P. Mencarelli (literal)

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Dipartimento di Chimica and Istituto CNR di Metodologie Chimiche-IMC, Sezione Meccanismi di Reazione c/o Dipartimento di Chimica, Sapienza Universita? di Roma, P.le A. Moro 5, 00185 Rome, Italy Dipartimento di Chimica and Centro di Eccellenza Materiali Innovativi Nanostrutturati, Universita di Perugia, via Elce di Sotto 8, 06123 Perugia, Italy (literal)

Titolo

Structural effects on the C-S bond cleavage in aryl tert-butyl sulfoxide radical cations (literal)

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+o-4+o have been observed in the steady-state photolysis experiments. By laser irradiation, the formation of 3-CN-NMQo (?max = 390 nm) and 1+o-4+o (?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 (kf) that decrease by increasing the electron donating power of the arylsulfinyl substituent from 1.8 × 106 s-1 (4+o) to 2.3 × 105 s-1 (1+o). 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 (? = 62 kcal mol-1) has been calculated for the C-S bond scission reaction in 1+o-4+o. (literal)

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