title: Mechanism of thiolate-disulfide exchange: addition-elimination or effectively S(N)2? Effect of a shallow intermediate in gas-phase direct dynamics simulations.
abstract: Direct dynamics trajectory simulations were performed for two examples of the thiolate-disulfide exchange reaction, that is, HS(-) + HSSH and CH(3)S(-) + CH(3)SSCH(3). The trajectories were computed for the PBE0/6-31+G(d) potential energy surface using both classical microcanonical sampling at the ion-dipole complex and quasi-classical Boltzmann sampling (T = 300 K) at the central transition state. The potential energy surface for these reactions involves a hypercoordinate sulfur intermediate. Despite the fact that the intermediate resides in a shallow well (less than 5 kcal/mol), very few trajectories follow a direct substitution path (the S(N)2 pathway). Rather, the mechanism is addition-elimination, with several trajectories sampling the intermediate for long times, up to 15 ps or longer.
authors.affiliation: Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409, United States.
authors.forename: Manikandan
authors.initials: M
authors.lastname: Paranjothy
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Siebert
authors.forename: William L
authors.initials: WL
authors.lastname: Hase
authors.forename: Steven M
authors.initials: SM
authors.lastname: Bachrach
mesh_terms: D004220:Disulfides / Q000737:chemistry*; D004583:Electrons; D005740:Gases / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D004220:Disulfides; D005740:Gases; D013438:Sulfhydryl Compounds