ORGANIC RADICAL CATIONS ABSTRACT METHYLENE FROM KETENE TO PRODUCE STABLE DISTONIC IONS

Gas-phase reactions of neutral ketene can be used to generate a variety of stable distonic radical cations, i.e., ions with a carbon radical center separated from the charge site by differing numbers of methylene units. Conventional radical cations abstract one to three CH2 groups (accompanied by loss of CO) from neutral ketene in consecutive reactions, the number of CH2 abstractions depending upon the structure of the reactant ion. All the productions studied were found to have distonic structures. For. example, ionized acetone abstracts a CH2 group from ketene to generate (CH3)2C+OCH2., an ion proposed earlier to occur as a transient intermediate during dissociation of ionized 1,2-epoxy-2-methylpropene. Besides conventional radical cations, distonic radical cations such as .CH2OCH2+ and .CH2CH2CH2CO+ also abstract methylene from ketene. The current evidence for these reactions supports a simple radical addition/elimination mechanism involving the terminal carbon of neutral ketene and the radical site of the ion. Hence, this approach can be used to homologate distonic radical cations.