Standard enthalpies of formation (Δf H° 298), standard entropies (S°(T)), and heat capacities (C p (T)) are calculated for dimethyl and ethyl methyl fluorinated ethers, both the parent and related radical species. The parent and radical species are utilized to determine carbon–hydrogen, carbon–fluorine, carbon–carbon, and carbon–oxygen bond dissociation energies (C–H, C–F, C–C, and C–O BDEs). The Δf H° 298 and BDEs are calculated using a variety of error-canceling isogyric and/or isodesmic reactions at the MN15/cc-pVTZ, CBS-QB3, and CBS-APNO levels of theory. Δf H° 298 calculations from the MN15 functional for these ether species are shown to have consistency with the CBS-QB3 and CBS-APNO composite methods with our recommended ideal gas phase Δf H° 298 values from the average of these two composite methods. C–F BDE values are shown to range overall between 111 and 128 kcal mol–1, the C–H BDEs are in the 93–106 kcal mol–1 range, the C–O BDEs are in the 83–107 kcal mol–1 range, and the C–C BDEs are in the 88–101 kcal mol–1 range. It is observed that as the number of fluorine atom substitutions increases, the C–H BDEs also increase. The number of fluorine atom substitutions on the carbon atom where the C–F bond is being broken has a larger influence than that of the total number of fluorine atom substitutions in the species. Optimized geometry parameters, moments of inertia, vibrational frequencies, and single bond internal rotor potentials are calculated at the MN15/cc-pVTZ level for contributions to entropy and heat capacities. Calculated thermochemical properties for CF-C-O-C, C-CF-O-C, and C-C-O-CF (i.e., 1-fluoroethyl methyl ether, 2-fluoroethyl methyl ether, and ethyl fluoromethyl ether) are utilized to develop fluorinated group additivity values (C/C/F/H2, C/C/F/H/O, and C/F/H2/O) for use in the group additivity (GA) method (as well as several carbon–hydrogen bond increment groups corresponding to radical formation). This work is of value in the development of detailed chemical kinetic mechanisms for use in atmospheric chemistry.

Fluorinated carboxylic acids and their radicals are becoming more prevalent in environmental waters and soils as they have been produced and used for numerous commercial applications. Understanding the thermochemical properties of fluorinated carboxylic acids will provide insights into the stability and reaction paths of these molecules in the environment, in body fluids, and in biological and biochemical processes. Structures and thermodynamic properties for over 50 species related to fluorinated carboxylic acids with two and three carbons are determined with density functional computational calculations B3LYP, M06-2X, and MN15 and higher ab initio levels CBS-QB3, CBS-APNO, and G4 of theory. The lowest energy structures, moments of inertia, vibrational frequencies, and internal rotor potentials of each target species are determined. Standard enthalpies of formation, Δf H 298 °, from CBS-APNO calculations show the smallest standard deviation among methods used in this work. Δf H 298 ° values are determined via several series of isodesmic and/or isogyric reactions. Enthalpies of formation are determined for fluorinated acetic and propionic acids and their respective radicals corresponding to the loss of hydrogen and fluorine atoms. Heat capacities as a function of temperature, C p(T), and entropy at 298 K, S 298 °, are determined. Thermochemical properties for the fluorinated carbon groups used in group additivity are also developed. Bond dissociation energies (BDEs) for the carbon–hydrogen, carbon–fluorine, and oxygen–hydrogen (C–H, C–F, and O–H BDEs) in the acids are reported. The C–H, C–F, and O–H bond energies of the fluorinated carboxylic acids are in the range of 89–104, 101–125, and 109–113 kcal mol–1, respectively. General trends show that the O–H bond energies on the acid group increase with the increase in the fluorine substitution. The strong carbon fluorine bonds in a fluorinated acid support the higher stability of the perfluorinated acids in the environment.