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

The spin adducts of triphenylsilyl, triphenylgermyl and triphenylstannyl radicals with γ-pyrone, γ-thiopyrone, thia-γ-pyrone and thia-γ-thiopyrone have been studied by ESR spectroscopy. The spectral parameters indicate that these radicals adopt the conformation where the O-M or S-M bonds are eclipsed with the 2 p z orbital of the γ-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.