An esr investigation on group IVb organometalloxy- and organometalthio-pyryl and thiapyryl radicals

The spin adducts of triphenylsilyl, triphenylgermyl and triphenylstannyl radicals with-gamma-pyrone, gamma-thiopyrone, thia-gamma-pyrone and thia-gamma-thiopyrone have been studied by ESR spectroscopy. The spectral parameters indicate that these radicals adopt the conformation where the O-M and S-M bonds are eclipsed with the 2pz orbital of the gamma-carbon, despite the absence of hindering substituent groups in proximity of the radical centre.
The electronic effects of sulphur and oxygen on the spin density distribution are also discussed.