DISTINGUISHING CONVENTIONAL AND DISTONIC RADICAL CATIONS BY USING DIMETHYL DISELENIDE

Dimethyl diselenide is demonstrated to be among the most powerful reag ents used to identify distonic radical cations. Most such ions readily abstract CH3Se. from dimethyl diselenide. The reaction is faster and more exclusive than CH3S. abstraction from dimethyl disulfide, a react ion used successfully in the past to identify numerous distonic ions. Very acidic distonic ions, such as HC+(OH)OCH2., do not undergo CH3Se. abstraction, but instead protonate dimethyl diselenide. In sharp cont rast to the reactivity of distonic ions, most conventional radical cat ions were found either to react by exclusive electron transfer or to b e unreactive toward dimethyl diselenide. Hence, this reagent allows di stinction of distonic and conventional isomers, which was demonstrated directly by examining two such isomer pairs. To be able to predict wh ether electron transfer is exothermic (and hence likely to occur), the ionization energy of dimethyl diselenide was determined by bracketing experiments. The low value obtained (7.9 +/- 0.1 eV) indicates that d imethyl diselenide will react with many conventional carbon-, sulfur-, and oxygen-containing radical cations by electron transfer. Nitrogen- containing conventional radical cations were found either to react wit h dimethyl diselenide by electron transfer or to be unreactive. (C) 19 96 American Society for Mass Spectrometry.