Oxygenated fluorocarbons are routinely found in sampling of environmental soils and waters as a result of the widespread use of fluoro and chlorofluoro carbons as heat transfer fluids, inert materials, polymers, fire retardants and solvents; the influence of these chemicals on the environment is a growing concern. The thermochemical properties of these species are needed for understanding their stability and reactions in the environment and in thermal process. Structures and thermochemical properties on the mono- to trifluoromethanol, CH3-xFxOH, and fluoromethyl hydroperoxide,CH3-xFxOOH (1 <= x <= 3), are determined by CBS-QB3, CBS-APNO, and G4 calculations. Entropy, S-298(degrees) and heat capacities, C-p(T)s (300 <= T/K <= 1500) from vibration, translation, and external rotation contributions are calculated on the basis of the vibration frequencies and structures obtained from the B3LYP/6-31+G(d,p) density functional method. Potential barriers for the internal rotations are also calculated from this method and used to calculate hindered rotor contributions to S-298(degrees) and C-p(T)'s using direct integration over energy levels of the internal rotational potentials. Standard enthalpies of formation Delta H-f(298)degrees (units in kcal moL(-1)) are CH2FOOH (-83.7), CHF2OOH (-138.1), CHF3OOH (-193.6), CH2FOO center dot(-44.9), CHF2OO center dot(-99.6), CF3OO center dot (-153.8), CHF2OOH (-101.9), CHF2OOH (-161.6), CF3OH (-218.1), CH2FO center dot (-49.1), CHF2O center dot (-97.8), CF3O (-150.5), CH2F center dot (-7:6), CHF2 center dot (-58.8), and CF3 center dot (-112.6). Bond dissociation energies for the R -OOH, RO-OH, ROO-H, R-OO center dot, RO-O-center dot, R -OH, RO-H, R-O-center dot, and R H bonds are determined and compared with methyl hydroperoxide to observe the trends from added fluoro substitutions. Enthalpy of formation for the fluoro-hydrocarbon oxygen groups C/F/H-2/O, C/F-2/H/O, C/F-3/O, are derived from the above fluorinated methanol and fluorinated hydroperoxide species for use in Benson's Group Additivity. It was determined that fluorinated peroxides require interaction terms O/CH2F/O, O/CHF2/O, and O/CF3/O, as opposed to the common (O/C/O) group in hydrocarbons, resulting from interactions of the peroxide oxygen with the fluorines. Hydrogen bond dissociation increment (HBI) groups are also developed.