Novel intramolecular hydrogen abstraction in the radical cation of some dioxacyclohexanes as studied by EPR spectroscopy and kinetic analysis

The radical cation of 2-methyl-1,3-dioxacyclohexane (1) in a frozen Freon matrix is found to release spontaneously a methyl radical and abstract intramolecularly a hydrogen atom from the resulting carbonium ion. Site selective deuteriation of 1 demonstrates that the abstraction occurs predominantly at the methylene groups adjacent to the oxygen atoms of the carbonium ion. The experimental result is analyzed in terms of the Siebrand theory for quantum mechanical tunnelling. By means of the harmonic oscillator approximation efficient recurrence formulae have been developed to calculate analytically the dual integration appearing in the theoretical rate constant.