ESR studies of ion-molecule reactions of ether, thioether, and olefin radical cations in the CF 2ClCFCl 2 matrix

Abstract

Several ion-molecule reactions of radical cations with their corresponding neutral molecules have been studied by ESR spectroscopy. These reactions were observed at low temperatures (80–130 K) in a mobile halocarbon matrix following the radiolytic generation of the radical cations from dilute solutions of the parent compound at 77 K. Ether and thioether radical cations react to produce neutral carbon-centered radicals with high regiospecificity, only the oxetan-2-yl radical being detected in the oxetane (trimethylene oxide) system, while the THF-2-yl species is produced in greater abundance than the THF-3-yl species from tetrahydrofuran (THF). The mechanism of these reactions is discussed in terms of either proton transfer from the radical cation or hydrogen atom transfer from the neutral molecule. For dimethyl sulfide, the dimer radical cation is observed prior to the formation of the •CH 2SMe radical. Similarly, the tetramethylethylene radical cation first forms the dimer radical cation which then undergoes a unimolecular reaction to give the 1,1,2-trimethylallyl radical. This is demonstrated by the fact that these two consecutive reactions can be observed separately rather than simultaneously by carefully controlled annealing, the dimer radical cation of tetramethylethylene being formed in high yield from the monomer cation before decomposing to the 1,1,2-trimethylallyl radical.