Understanding the interaction of O2 with ketones on metal oxide surfaces is important for the photo-oxidation of toxic organic molecules. The consecutive reaction steps of acetone molecules with oxygen adatoms (O a's) on partially oxidized TiO2(110) surfaces have been studied using high-resolution scanning tunneling microscopy (STM) at 300 K. The sequential isothermal STM images reveal two types of acetone-Oa species as a result of reactions of acetone with an oxygen adatom and a bridging bound oxygen vacancy (VO). One such species is the Ti 5c-bound acetone-Oa diolate formed from Ti 5c-bound acetone reacting with Oa. The diolate is mobile at 300 K and can assist the diffusion of surface Oa by exchanging the acetone oxygen with the Oa. The second acetone-Oa species is the VO-bound acetone-Oa complex formed from a V O-bound acetone reacting with an Oa located on the neighboring Ti row. The VO-bound complex is stationary at 300 K. This species has not been reported previously.