Structure and Reactivity of the Radical Cations of Methyl tert-Butyl Ether in Condensed Phase: An ESR and Quantum Chemical Study

The structure of the methyl tert-butyl ether (MTBE) radical cation and mechanism of its thermal and photochemical reactions in irradiated freons (CFCl₃, CF₂ClCFCl₂, and CF₃CCl₃) were studied. Radical products of MTBE radiolysis in the liquid phase were investigated by the spin trapping technique. The quantum-chemical calculations of the structure of MTBE radical cations and products of their transformations were carried out by density functional theory (DFT) and ab initioMP2 methods. The primary MTBE radical cations are stabilized in dilute solutions in CFCl₃and CF₃CCl₃. The ion–molecule reaction (proton transfer from the radical cation) was found to occur in concentrated solutions in CFCl₃immediately during irradiation. The action of light ( = 436 to 546 nm) at 77 K on the MTBE radical cation in CFCl₃and CF₃CCl₃matrices results in intramolecular migration of the methyl group to yield the distonic radical cation (CH₃)₂ ^.CO⁺(CH₃)₂. The primary MTBE radical cations undergo an irreversible transformation with methane elimination resulting in formation of the 2-methoxypropene radical cation ^.CH₂=⁺(₃)₃in CFCl₃and CF₃CCl₃matrices in the temperature range 110–130 K. In the case of CF₂ClCFCl₂matrix, such a reaction occurs during irradiation at 77 K. Using the spin trapping technique, it was shown that the liquid-phase radiolysis of the neat ether resulted in the formation of fragmentation products (^.CH₃,CH₃^., and t-BuO^. radicals) from the primary radical cations, as well as the products of their rearrangements and ion–molecule reactions.