Isomerization and dissociation of ionized dimethyl sulfoxide: A theoretical insight

Guy Bouchoux (1) , H.T. Le (2, 3) , M.T. Nguyen (2)

1 DCMR - Laboratoire des mécanismes réactionnels
2 Department of Chemistry
3 Group of Computational Chemistry

The potential energy profile associated with CH3 and OH losses from the dimethyl sulfoxide radical cation, CH3SOCH3*+, 1, has been examined at the G2(MP2,SVP) level. Isomerization of 1 into its aci-tautomer, CH3S(OH)CH2*+, 2, by a 1,3-hydrogen migration constitutes the initial and energy-determining step of both dissociations. This explains the observation of identical appearance energies for the corresponding fragment ions. Heats of formation values of 702, 794, and 795 kJ/mol are obtained from atomization energies at the G2(MP2,SVP) level for CH2SOH+, CH3SO+, and CH2SCH3+, respectively. The kinetics of the reactions 2 CH2SCH3+ + *OH and 2 ? CH2SOH+ + *CH3 have been examined by using a RRKM-type orbiting transition state theory. Explicit consideration of the rotational effect is crucial, inducing the latter process to be dominant at a high internal energy of the precursor ions 2. This offers the reason for why the m/z 63 (CH2SOH+) ions are more abundant than the m/z 61 (CH2SCH3+) in the mass spectrum of dimethyl sulfoxide even though the OH loss represents the less energy demanding reaction.

Guy Bouchoux, H.T. Le, M.T. Nguyen. Isomerization and dissociation of ionized dimethyl sulfoxide: A theoretical insight. Journal of Physical Chemistry A, 2001, 105 (49), pp.11128-11133. ⟨10.1021/jp013201d⟩. ⟨hal-00918623⟩