Thermochemical properties of tert-isooctane hydroperoxide and its radicals are determined by computational chemistry. Enthalpies are determined using isodesmic reactions with B3LYP density function and CBS QB3 methods. Application of group additivity with comparison to calculated values is illustrated. Entropy and heat capacities are determined using geometric parameters and frequencies from the B3LYP/6-31G(d,p) calculations for the lowest energy conformer. Internal rotor potentials are determined for the tert-isooctane hydroperoxide and its radicals in order to identify isomer energies. Recommended values derived from the most stable conformers of tert-isooctane hydroperoxide of are -77.85 ± 0.44 kcal mol(-1). Isooctane is a highly branched molecule, and its structure has a significant effect on its thermochemistry and reaction barriers. Intramolecular interactions are shown to have a significant effect on the enthalpy of the isooctane parent and its radicals on peroxy/peroxide systems, the R• + O2 well depths and unimolecular reaction barriers. Bond dissociation energies and well depths, for tert-isooctane hydroperoxide → R• + O2 are 33.5 kcal mol(-1) compared to values of ∼38 to 40 kcal mol(-1) for the smaller tert-butyl-O2 → R• + O2. Transition states and kinetic parameters for intramolecular hydrogen atom transfer and molecular elimination channels are characterized to evaluate reaction paths and kinetics. Kinetic parameters are determined versus pressure and temperature for the chemically activated formation and unimolecular dissociation of the peroxide adducts. Multifrequency quantum RRK (QRRK) analysis is used for k(E) with master equation analysis for falloff. The major reaction paths at 1000 K are formation of isooctane plus HO2 followed by cyclic ether plus OH. Stabilization of the tert-isooctane hydroperoxy radical becomes important at lower temperatures.

Thermochemical properties for isooctane, its internal rotation conformers, and radicals with corresponding bond energies are determined by use of computational chemistry. Enthalpies of formation are determined using isodesmic reactions with B3LYP density function theory and composite CBS-QB3 methods. Application of group additivity with comparison to calculated values is illustrated. Entropy and heat capacities are determined using geometric parameters, internal rotor potentials, and frequencies from B3LYP/6-31G(d,p) calculations for the lowest energy conformer. Internal rotor potentials are determined for the isooctane parent and for the primary, secondary, and tertiary radicals in order to identify isomer energies. Intramolecular interactions are shown to have a significant effect on the enthalpy of formation of the isooctane parent and its radicals. The computed standard enthalpy of formation for the lowest energy conformers of isooctane from this study is -54.40 ± 1.60 kcal mol(-1), which is 0.8 kcal mol(-1) lower than the evaluated experimental value -53.54 ± 0.36 kcal mol(-1). The standard enthalpy of formation for the primary radical for a methyl on the quaternary carbon is -5.00 ± 1.69 kcal mol(-1), for the primary radical on the tertiary carbon is -5.18 ± 1.69 kcal mol(-1), for the secondary isooctane radical is -9.03 ± 1.84 kcal mol(-1), and for the tertiary isooctane radical is -12.30 ± 2.02 kcal mol(-1). Bond energy values for the isooctane radicals are 100.64 ± 1.73, 100.46 ± 1.73, 96.41 ± 1.88 and 93.14 ± 2.05 kcal mol(-1) for C3•CCCC2, C3CCCC2•, C3CC•CC2, and C3CCC•C2, respectively. Entropy and heat capacity values are reported for the lowest energy homologues.

Density functional theory (DFT) and composite ab initio based calculations are performed on trifluoroethane along with intermediate radicals, parent molecules of the radicals, and products related to the reaction of hydroxyl radical with 1,1,2-trifluoroethene, as a reference for hydrofluoroolefins (HFO). Potential energy barriers for internal rotations have been computed. Calculated torsional potentials are incorporated into the determination of entropy, S° 298, and heat capacities as a function of temperature, Cp (T), for each target molecule. Six isodesmic or isogyric reactions and five calculation methods are used to determine heats of formation at 298 K (Δf H 298) in kcal mol–1 of each target species. The CBS-APNO method shows the best agreement with experimental data in comparisons from 16 reference reactions on Δrxn H of each method. The lowest configuration structures of each target species are reported. Intramolecular hydrogen bonds between the hydroxyl hydrogen atom and the fluorine atom on the adjacent carbon can stabilize molecules by up to 3 kcal mol–1. R–OH bond dissociation energies are observed to increase with the number of fluorine atoms on the carbon connected to hydroxy group. Recommended Δf H 298 values in kcal mol–1 derived from the most stable conformers are CF2(OH)­CH2F (−213.0), CF2(O•)­CH2F (−148.6), CF2(OH)­C•FH (−162.4), CHF2CHFOH (−207.5), CHF2C•FOH (−158.3), C•F2CHFOH (−155.5), CHF2CHFO• (−150.4), CF3CH2OH (−212.5), and CF3C•HOH (−167.9).

Fluorinated olefins are valued chemicals in industry, especially as heat transfer fluids in refrigeration applications. As these volatile compounds are widely used, they may be released into the atmosphere, and investigation of their reactions in the atmosphere are therefore of importance. The kinetic analysis of the reaction mechanisms of trifluoroethene (CF 2 CHF) with hydroxyl radicals is studied using computational chemistry at the M06-2X level with the 6-311+ +G(2d,d,p) and aug-cc-pVDZ basis sets as well as the composite CBS-QB3 method. Rate coefficients for the proposed mechanisms are calculated using transition state theory (TST) with tunneling corrections. The calculated rate constants for OH addition to CF 2 CHF are in excellent agreement with experimental values. Kinetic parameters as a function of temperature and pressure are evaluated for the chemically activated formation and unimolecular dissociation of hydroxylfluoroalkyl intermediates. Important forward reactions result in adduct stabilization, H atoms, hydrogen fluoride (HF) via molecular elimination, and formation of fluorinated carbonyl radicals with CF 2 (O) and CHF(O) product channels. Stabilization of initial adducts along with HF elimination are important reaction pathways under high pressure and low temperatures. Important HF eliminations and H atom transfers primarily involve H atoms from the hydroxyl group, as the C−H bonds on or adjacent to carbons with F atoms are stronger and show high barriers to H atom transfer.

Structures, enthalpy (Δ(f)H°(298)), entropy (S°(T)), and heat capacity (C(p)(T)) are determined for a series of nitrocarbonyls, nitroolefins, corresponding nitrites, and their carbon centered radicals using the density functional B3LYP and composite CBS-QB3 calculations. Enthalpies of formation (Δ(f)H°(298)) are determined at the B3LYP/6-31G(d,p), B3LYP/6-31+G(2d,2p), and composite CBS-QB3 levels using several work reactions for each species. Entropy (S) and heat capacity (C(p)(T)) values from vibration, translational, and external rotational contributions are calculated using the rigid-rotor-harmonic-oscillator approximation based on the vibration frequencies and structures obtained from the density functional studies. Contribution to Δ(f)H(T), S, and C(p)(T) from the analysis on the internal rotors is included. Recommended values for enthalpies of formation of the most stable conformers of nitroacetone cc(═o)cno2, acetonitrite cc(═o)ono, nitroacetate cc(═o)no2, and acetyl nitrite cc(═o)ono are -51.6 kcal mol(-1), -51.3 kcal mol(-1), -45.4 kcal mol(-1), and -58.2 kcal mol(-1), respectively. The calculated Δ(f)H°(298) for nitroethylene c═cno2 is 7.6 kcal mol(-1) and for vinyl nitrite c═cono is 7.2 kcal mol(-1). We also found an unusual phenomena: an intramolecular transfer reaction (isomerization) with a low barrier (3.6 kcal mol(-1)) in the acetyl nitrite. The NO of the nitrite (R-ONO) in CH(3)C(═O')ONO moves to the C═O' oxygen in a motion of a stretching frequency and then a shift to the carbonyl oxygen (marked as O' for illustration purposes).