Thermochemical properties of CHFO and CF2O and their derivatives were calculated by using coupled-cluster theory (U)CCSD(T) calculations with the aug-cc-pVnZ (n = D, T, Q, 5) basis sets extrapolated to the complete basis set limit with additional corrections. The predicted properties include the following. Enthalpies of formation (298 K, kcal/mol): Delta H-f(CF2O) = -144.7, Delta H-f(CHFO) = -91.1, Delta H-f(CFO center dot) = -41.6. Bond dissociation energy (0 K, kcal/mol): BDE(CFO-F) = 120.7, BDE(CHO-F) = 119.1, BDE(CFO-H) = 100.2. Ionization potential (eV): IP1(CF2O) = 13.04, IP2(CF2O) = 14.09, IP1(CHFO) = 12.41, IP2(CHFO) = 13.99, IP1(CFO center dot) = 9.34. Proton affinity (298 K, kcal/mol), PA(o)(CF2O) = 148.8, PA(o)(CHFO) = 156.7, PA(F)(CHFO) = 154.5 kcal/mol. Electron affinity: EA(CFO center dot) = 2.38 eV. Triplet-singlet separation gap (eV): Delta ET1-S0(CF2O) = 4.47, Delta ET1-S0(CHFO) = 4.36. Triplet-triplet transition energy (eV): Delta ET2-T1(CF2O) = 0.44. The new calculated values contribute to solving some persistent discrepancies in the literature. The effects of F-atoms on thermochemical parameters are not linearly additive, and the changes are largely dominated by the first F-substitution. On the basis of the calculated proton affinities of CF2O and CF3OH, the nucleophilicities of the oxygen atoms are, within computational errors, the same in both compounds.