In this paper, ab initio calculations are performed on carbonyl oxides RR^1COO (R, R^1=H, F, CH~3) using 6-31G basis set in order to study the electronic structures of the ground states. All geometries are optimized with the energy gradient technique. The calculated results predict that the stable structure is a diradical, the relative energies between singlets and triplets are influenced by the substituents. And the ground states for H~2COO, H(CH~3)COO, and (CH~3)~2COO are singlet (^1A), the ground states for HFCOO, and F~2COO are triplet (^3A). The cis forms of HFCOO and H(CH~3)COO are found to be more stable than the corresponding transforms.

Key words: ELECTRONIC STRUCTURE, OXIDE, CARBONYL GROUP, SINGLET, TRIPLET