O-protonated sulfine CH 2=S=OH +. Its generation from ionized dimethylsulfoxide by delayed dissociation

Abstract

Mass spectrometry based experiments show that dimethylsulfoxide (DMSO) radical cations, CH 3S(=O)CH +. 3, dissociating with rate constants < 10 5 s −1 form not CH 3S=O +, 1, but rather the more stable isomer CH 2=S=OH +, 2, via the aci-tautomer CH 2=S(OH)CH +. 3. It is proposed that the previously measured appearance energy for loss of CH 3 from DMSO corresponds to 2, leading to Δ H f( 2)= 736 kJ/mol. Ab initio calculations indicate that Δ H f( 1) may need to be revised upwards to about 815 kJ/mol. Previous labelling results on DMSO are in excellent agreement with the formation of 2.