Thermodynamic Properties: Enthalpy, Entropy, Heat Capacity, and Bond Energies of Fluorinated Carboxylic Acids

Abstract

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.

Thermochemistry of Species in Gas-Phase Thermal Oxidation of C2 to C8 Perfluorinated Carboxylic Acids

“…The high-accuracy values from Goldsmith are already being used as references within this work, as are various NASA polynomials from the Third Millennium Database . Other literature values are from the work of Bozzelli and co-workers , and that of Altarawneh and co-workers. Comparisons are shown in Table , where enthalpies are reported in kcal mol –1 , and entropies and heat capacities are in cal mol –1 K –1 .…”

“…First, if values of Δ f H 0K ° are in agreement, then the disagreement in Δ f H 298K ° would result from slight differences in the converged structures, leading to differences in C p ° ( T ). Additionally, the use of different schemes to calculate heats of formation can also be a cause if schemes were used to calculate values at 298 K. The calculations of Bozzelli and co-workers , were performed using weighted averages of heats of formation calculated by isodesmic or isogyric schemes at various levels of both DFT and composite methods and have associated uncertainties based both on the uncertainty in the reference species and the nature of the weighted average of multiple methods. Furthermore, the calculations of Altarawneh and co-workers were performed at the M06-2X/6-311+G­(d,p) level, which has been shown by our benchmarking calculations to have higher deviations in Δ f H 0K ° than both G4 and our DFT method of choice, M06-2X-D3(0)/def2-QZVPP.…”

pKa as a Predictive Descriptor for Electrochemical Anion Adsorption

“…Surprisingly, we find (using the same DFT methodology as in the prior work) that the adsorption energy of these neutral carboxyl radicals does not vary significantly upon changing the functional group bound to the acetate, and that there is no clear correlation between the adsorption energy of these radicals and their homolytic O−H bond dissociation energies. While the existence of such a correlation may be sensitive to the accuracy of the DFT calculations, DFT calculations with more advanced functionals support that the differences in O−H homolytic bond dissociation energies for these species are much smaller than differences in their heterolytic bond dissociation energies; the difference between acetic acid and trifluoroacetic acid (the species with the largest difference in heterolytic O−H bond dissociation energy) is only ~0.15 eV [31] . Given that the radical adsorption energies do not vary significantly between these carboxylates, that must mean that it is the variation in electron affinity across these carboxylates that is solely (or at least primarily) responsible for the variation in the anion adsorption energy.…”

“…While the existence of such a correlation may be sensitive to the accuracy of the DFT calculations, DFT calculations with more advanced functionals support that the differences in OÀ H homolytic bond dissociation energies for these species are much smaller than differences in their heterolytic bond dissociation energies; the difference between acetic acid and trifluoroacetic acid (the species with the largest difference in heterolytic OÀ H bond dissociation energy) is only ~0.15 eV. [31] Given that the radical adsorption energies do not vary significantly between these b) Similar to a), except the approximate solvation energy of the anion [28] has been subtracted from the anion adsorption energy, and plotted against the experimentally measured gas-phase heterolytic OÀ H bond dissociation energy. [29] A linear correlation is still observed, with a steeper slope than that found in a), suggesting that this correlation is not a result of solvation; in fact, accounting for solvation strengthens the correlation (between anion-surface and anion-proton bond strength).…”

Study on the mechanical properties of micropore organic polymer membranes

“…The electron-attracting uorine resulted in an electron bias within the C-F bond towards the uorine atom, for exceptional stability. Carbon-uorine bonds (485 kJ/mol) exhibited higher binding energies, more pronounced dipole moments, and greater charge densities compared to hydrocarbon bonds (413 kJ/mol) [39]. As a result, C-F bonds display signi cantly greater resilience than C-H bonds.…”