Conformational inversion in dihydrobenzodioxine radical cations

The kinetics of the inversion of the dihydrodioxine ring in the radical cat ions of six dihydrobenzo[1,4]dioxines have been determined by EPR spectrosc opy. In the nine compounds for which results are now available, the activat ion energies E-a range from 22.6 to 47.6 kJ mol(-1), and the pre-exponentia l factors, log A, from 12.8 to 16.2. The barriers appear to be always highe r than those in the corresponding hydrocarbon radical cations. Removal of o ne electron from hexaoxadodecahydrotriphenylene 9 to give the radical catio n causes the value of Delta G double dagger 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 t erms of the various stereoelectronic effects which may be involved.