title: S-S bond mesolysis in alpha,alpha'-dinaphthyl disulfide radical anion generated during gamma-radiolysis and pulse radiolysis in organic solution.
abstract: A dissociation mechanism of the S-S bond in the alpha,alpha'-dinaphthyl disulfide radical anion (NpSSNp*-) in organic solution was investigated on the basis of transient absorption measurements and DFT calculations. NpSSNp*- generated during gamma-radiolysis of NpSSNp in MTHF at 77 K showed the absorption band at 430 nm, which shifted to 560 nm with an increase of the ambient temperature up to room temperature. With the aid of DFT calculations at the B3LYP/6-31G(d) level, the shift of the absorption band was interpreted in terms of molecular conformational changes of NpSSNp*- due to the elongation of the S-S bond. It was observed that NpSSNp*- dissociates into naphthylthiyl radical and thionaphtholate anion in organic solution with a first-order rate constant in the magnitude of 10(6) s-1. From Arrhenius plots of the decay rate constants of NpSSNp*- in a temperature range of 160-293 K, an activation energy for the S-S bond cleavage in NpSSNp*- in solution was determined along with a frequency factor. Based on the state energies of NpSSNp*- calculated at the B3LYP/6-31G(d) level, a Morse-like energy potential for the S-S bond cleavage of NpSSNp*- is depicted as a function of the S-S bond distance.
authors.affiliation: Department of Chemistry, Gunma University, Kiryu 376-8515, Japan. yamaji@chem.gunma-u.ac.jp
authors.forename: Minoru
authors.initials: M
authors.lastname: Yamaji
authors.forename: Sachiko
authors.initials: S
authors.lastname: Tojo
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Takehira
authors.forename: Seiji
authors.initials: S
authors.lastname: Tobita
authors.forename: Mamoru
authors.initials: M
authors.lastname: Fujitsuka
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Majima
mesh_terms: D000838:Anions / Q000737:chemistry; D004220:Disulfides / Q000737:chemistry*; D005609:Free Radicals / Q000737:chemistry; D008958:Models, Molecular; D009284:Naphthols / Q000737:chemistry*; D011675:Pulse Radiolysis; D012996:Solutions; D013057:Spectrum Analysis; D013816:Thermodynamics
chemical_list: D000838:Anions; D004220:Disulfides; D005609:Free Radicals; D009284:Naphthols; D012996:Solutions