Six new monoadducts Of C-70 with oxygen species have been prepared, isolated, and characterized following ozonation Of C-70 solutions. The initial products are two ozonide monoadducts, identified as a,band c,c-C70O3. These ozonides lose O-2 through themnolysis or photolysis to form various isomers Of C70O. The a,b-C70O3 isomer dissociates through thermolysis with a decay time of 14 min at 296 K to form the [6,6]-closed epoxide a,b-C70O. When photolyzed, it instead forms a [5,6]-open oxidoannulene identified as a,a-C70O. These reactions mimic those seen for C60O3. By contrast, the c,c-C70O3 isomer, which has a thermolysis lifetime of 650 min at 296 K, decays thermally only to an oxidoannulene deduced to be d,d-C70O. Photolysis Of c,c-C70O3 produces a mixture of the oxidoannulenes b,c-C70O and c,d-C70O plus a minor amount of the cc-epoxide. All four C70O oxidoannulene isomers undergo photoisomerization, giving eventually the a,b- and c,c-C70O epoxides.