Gas-phase Reactions of Isomeric Carbene and Distonic Radical Anions Derived from Methylthioacetonitrile with Dimethyl Disulfide

Abstract

The gas-phase ionhnolecule reactions of the CH,SCDCN, CH,SCCN and 'CH,SCDCN ions formed in the reaction of the 0-' ion with CH,SCD,CN have been studied with the use of Fourier-transform ion cyclotron resonance (FTICR). In the reaction of the CH,SCDCN carbanion with the model substrate, dimethyl disulfide, a CH,SD molecule is expelled from the collisioncomplex with the indicated formation of a (CH,S),CCN ion. In the reactions ofthe carbene radical anion, CH,SCCN, loss of a CH,S radical occurs and the formation of an ion with a (CH,S),CCN structure is again indicated. A distinct reactivity is observed for the distonic radical anion, 'CH,SCDCN, which reacts with dimethyl disulfide by the competing losses of CH,SH and CH,S from the collision complex. It is proposed that the loss of CH,SH yields a CH,SCHSCDCN or CH,SCHS&CN radical anion, whereas the loss of CH,S is proposed to lead to a CH,SCH,SCDCN carbanion. The formation of these species in the reactions of the 'CH,SCDCN ion is discussed as involving an initial radical or nucleophilic attack on one of the sulfur atoms in dimethyl disulfide followed by cleavage of the sulfur-sulfur bond prior to the loss of a CH,SH molecule and/or a CH,S radical. The structure, stability and unimolecular dissociations of distonic ions have been studied extensively,'-' whereas insight into the gas-phase bimolecular chemistry of such ions is somewhat more limited.6,7 The interest in the bimolecular chemistry of distonic ions, however, may be considered to be of general significance, since the formal separation of the radical and charge sites offers the possibility of examining reactions which involve primarily only one of these centers. With respect to distonic radical cations, a number of studies indicate that these species can react differentIy from the isomeric conventional radical cations and/or the related cations. Notably, a distonic radical cation may react by hydrogen atom abstraction or a formal transfer of a functional group originating from the substrate, whereas the conventional radical cations often prefer to react by charge exchange if this process is exothermic.6, For example, the distonic radical cation, 'CH,CH,CH2C0 reacts with CH,SSCH, by a CH,S radical