Thermochemistry of Halogenomethanes

Systematic errors in DFT calculations of haloalkane heats of formation

“…Displayed in Table 1 are the experimental enthalpies of formation of the halomethanes (1A) and haloethanes (1B) taken from the literature 12–23. Numbers in brackets refer to the specific reference.…”

“…We have chosen to compute enthalpies of formation in the series of 15 fluoro‐, chloro‐ and chlorofluoromethanes (studied earlier with the G2 method9), and in the series of 18 fluorinated and chlorinated ethanes, C 2 H x R 6‐x , R = F, Cl, x = 0–6. Moderately to very accurate experimental values of Δ f H ° have been reported for almost all of these molecules,12–23 which will permit a realistic assessment of the accuracy of DFT calculations of haloalkane formation enthalpies.…”

Synthesis and thermochemical properties of NF2-containing energetic salts

“…For example, in the JANAF tables [24] the value for D f H 298 (CH 3 F, g) is given as À56 AE 6.9; À60 AE 3.5 kcal mol À1 (NIST benchmark database) [25]. Different calculation methods also lead to quite different results: À57.4 AE 1.2 kcal mol À1 (based on isogyric and hydrogenation reactions) [26]; À55.6 AE 2 kcal mol À1 [27]; and À55.9 AE 1 kcal mol À1 [28], À55.8 to À58.6 kcal mol À1 using atomization and isodesmic bond separation reactions when correlated to CF 4 using G2, G2(MP2), CBS-4, CBS-Q, CBS-APNO, BAC-MP4, etc. [29].…”

Mechanism and Kinetics of the Hydrogen Abstraction Reaction of C₂H₃ with CH₃F

“…Since a large absolute value of the imaginary frequency means a narrow width of the potential barrier, 50,51 which in turn benefits the tunneling effect, therefore, the quantum tunneling effect may be significant and plays a key role in the calculated rate constants for the title reaction system. The reaction energies (ΔE) and classical potential barriers (ΔE ≠ ) calculated at different levels are listed in Table 2, including the proposed active energy 39 and the reaction enthalpy derived from the heats of formation 44,[52][53][54] . Note that the error limits of the reaction enthalpy were estimated by adding the maximum uncertainties of ΔHf for the reference compounds.…”