Conformational inversion in dihydrobenzodioxine radical cations

Abstract

The kinetics of the inversion of the dihydrodioxine ring in the radical cations of six dihydrobenzo[1,4]dioxines have been determined by EPR spectroscopy. In the nine compounds for which results are now available, the activation energies E_a range from 22.6 to 47.6 kJ mol^–1, and the pre-exponential factors, log A, from 12.8 to 16.2. The barriers appear to be always higher than those in the corresponding hydrocarbon radical cations. Removal of one electron from hexaoxadodecahydrotriphenylene 9 to give the radical cation causes the value of ΔG ^‡ at 155 K to increase from 30.0 kJ mol^–1 in 9 to 36.7 kJ mol^–1 in 9^˙+. The results are discussed in terms of the various stereoelectronic effects which may be involved.