The effect of fluorine substitution on the structure of oxiranes and on the energetics of the oxiranylcarbinyl radical ring opening

Fluorine substituent effects on the structure of oxirane and on the kinetic behavior of oxiranylcarbinyl radicals, as determined by DFT calculations, have been found to be similar to those observed for the analogous fluorinated cyclopropylcarbinyl radical systems. A structural and energetic analysis showed that a stereoelectronic effect involving preferential interaction of the semi-occupied atomic orbital of the radical with the weaker ring bond is the major factor that contributes to the regiochemistry of the ring opening of fluorinated oxiranylcarbinyl radicals. With low and potentially zero activation barriers, 3,3-difluorooxiranylcarbinyl radical and cation undergo ring opening with CO bond cleavage and CC cleavage, respectively.