ESR spectra of phosphorus-containing fullerenyl radicals C-.(60)-P(O)(
OPri)(2) and C-.(60)-P(O)(OEt)Ph were studied at low temperatures (193
-273 K). A decrease in the rate of rotation of organophosphorus group
around the C-P bond results first in line broadening and then in the a
ppearance of two doublets due to two ''extreme'' conformations, which
have different g-factors and hyperfine coupling constants (HCC) of the
unpaired electron with the P-31 nucleus. The kinetic and thermodynami
c parameters of the conformational isomerism were calculated.