Studies of Two-Center Three-Electron S∴S Bonds in [<i>n</i>-Pr₂S∴S<i>n</i>-Pr₂]⁺ and [<i>i</i>-Pr₂S∴S<i>i</i>-Pr₂]⁺:  Thermochemistry of Adduct Formation and MS/MS Metastable and Collision-Induced Dissociation Spectra of the Adducts

Abstract

Gas-phase ion−molecule association reactions of n -propyl sulfide radical cation ([ n -Pr 2 S] + ) with n -propyl sulfide ( n -Pr 2 S) were studied by equilibrium methods in CO 2 bath gas to investigate the bond energy of the 2c-3e bond. The 2c-3e S∴S bond enthalpy in [ n -Pr 2 S∴S n -Pr 2 ] + was determined to be 119 kJ/mol at 507 K. This results in a scaled S∴S bond energy of 123 kJ/mol. The S∴S bond enthalpy in the i -propyl sulfide dimer cation ([ i -Pr 2 S∴S i -Pr 2 ] + ) could not be determined due to a fragmentation reaction, the loss of an i -propyl group. MS/MS metastable and collision-induced dissociation experiments were carried out to determine metastable fragmentation pathways and to aid in structure analysis. The results are consistent with association products containing 2c-3e bonds; statistical unimolecular metastable fragmentation of the association adduct, [ i -Pr 2 S∴S i -Pr 2 ] +, confirms the loss of the i -propyl group, which prevented the equilibrium experiments.