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 Ea 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.