Thermochemical properties from G3MP2B3 calculations,Set‐2: Free radicals with special consideration of CH2CH?C•CH2, cyclo−•C5H5, •CH2OOH,HO?•CO,and HC(O)O•

After a set of 32 free radicals was presented (Int J Chem Kin 34, 550–560, 2002), an additional 60 free radicals (Set‐2) were studied and characterized by energy minimum structures, harmonic vibrational wave numbers ω_e, moments of inertia I_A, I_B, and I_C, heat capacities C^o_p(T), standard entropies S^o(T), thermal energy contents H^o(T) ? H^o(0), and standard enthalpies of formation Δ_fH^o(T) at the G3MP2B3 level of theory. Thermodynamic functions at T = 298.15 K are presented and compared with recent experimental values where these are available. The mean absolute deviation between calculated and experimental Δ_fH^o(298.15) values by the previous set of 32 radicals is 3.91 kJ mol^?1. For the sake of comparison, only 49 species out of the 60 radicals of Set‐2 are characterized by experimental enthalpies of formation, and the corresponding mean absolute deviation between calculated and experimental Δ_fH^o(298.15) values is 8.96 kJ mol^?1. This situation is cause for demand of more and also more accurate experimental values. In addition to the above properties, parent molecules of a large set of the respective radicals are calculated to obtain bond dissociation energies D^o(298.15). Radical stabilization owing to resonance is discussed using the complete sets of total atomic spin densities ρ as a support. In particular, a short review about recent developments of the first‐order Jahn–Teller radical c‐C₅H₅^? is presented. In addition, radicals with negative bond energies are described, such as ^?CH₂OOH where the reaction path to CH₂O + HO^? has been calculated, as well as radicals which have two different parent molecules, for example C?N? O^?. For the reaction HO^? + CO → H^? + CO₂, two reaction paths are characterized by a total of 14 stationary points where the intermediate radicals HO? ^?CO and HC(O)O^? are involved. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 661–686, 2004     

Enthalpies of formation of acetyl radicals

The database on the enthalpies of formation (Δ_f H ^○) of aliphatic acetyl radicals of the RC·(O) type is analyzed and extended. Δ_f H ^○ values are estimated for the first time for three compounds on the basis of experimental data. The data were analyzed using the additive group approach with the determination and correction of parameters. Good correspondence between the Δ_f H ^○(RC·(O)) values calculated according to parameters with experimental data is observed.     

Determination of enthalpies of formation of organic free radicals from bond dissociation energies 2. Halosubstituted radicals

The enthalpies of formation (ΔH _f ^o) for 23 halosubstituted radicals were determined from the published data on bond dissociation energies. The ΔH _f ^o values of the corresponding molecules necessary for the calculation of ΔH _f ^o of the radicals were taken from handbooks or calculated by the additive-group method. The conjugation energies of the radicals are calculated, and the effect of substituents at the π-system on these values was shown. Errors of determination of the ΔH _f ^o values of the radicals were estimated. For Part 1, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 643–646, April, 1998.     

Enthalpies of formation for alkylcarbonyl radicals

The data on enthalpies of formation (Δ_f H ^○) of alkylcarbonyl radicals are expanded to 22 items. The reference value of Δ_f H ^○ for diacetylperoxide in the gas phase (?485.5 kJ/mol) is determined via recalculation from evaporation enthalpy (n-C₅H₁₁C(O)O)₂. The Δ_f H ^○ values of 22 diacylperoxides (gaseous) are calculated and used in combination with the literature data on dissociation energies of D(O-O) bonds in them to determine the Δ_f H ^○ of corresponding radicals. The interrelation between structure and properties (the enthalpy of formation) is considered, and the parameters for the calculated prediction of Δ_f H ^○ are found.     

Determination of enthalpies of formation of organic free radicals from bond dissociation energies

The values of C−H and C−I bond dissociation energies were used to calculate the enthalpies of formation (δH _f ^o of 20 cyclic and conjugated hydrocarbon radicals (R′). The values of δH _f ^o (R′) were analyzed in terms of the quantitative structure-property correlation based on the additive-group model, and the reliability of these data was shown. Based on the correlation, several strain energies of cycles and energies of conjugation of a lone electron with a ρ-system were calculated. The additive-group method for calculation of δH _f ^o can be extended for radicals of the naphthalyl type. For Part 2, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 286–288, February, 1999.     

The standard enthalpies of formation of alkoxy-NNO-azoxy compounds

The standard enthalpies of combustion Δ_c H ^o and formation Δ_f H ^o of seven alkoxy-NNO-azoxy compounds containing the-N⁺(O^?)=NO-characteristic group were determined by combustion in a calorimetric bomb in the atmosphere of oxygen. The contribution of this group to the Δ_f H ^o enthalpies of the substances studied was calculated. The Δ_f H ^o enthalpies found by the method of group contributions were in satisfactory agreement with experimental data.     

Enthalpies of the formation of aliphatic carbonyl-containing radicals

A collection of data on enthalpies of the formation(Δ_f H ^o) of aliphatic carbonyl-containing radicals is analyzed and expanded. The Δ_f H ^o values for 29 carbonyl-containing radicals are determined for the first time, and are strongly revised for 17 carbonyl-containing radicals using the literature data on the dissociation energies of the bonds in molecules. The data is analyzed on the basis of the structureproperty (enthalpy of formation) relation within the additive-group approach, with the determination and specification of the parameters. It is concluded that the Δ_f H ^o values of carbonyl-containing radicals calculated from the obtained parameters (a total of 96 compounds was considered) agree well with the experimental data.     

The enthalpies of formation of bis-(benzene)molybdenum and of bis-(toluene)tungsten

Microcalorimetric measurements at 520–523 K of the heats of thermal decomposition and of iodination of bis-(benzene)molybdenum and of bis-(toluene)tungsten have led to the values (kJ mol^?): ΔH^o_f[Mo(η-C₆H₆)₂, c] = (235.3 ± 8) and ΔH^o_f[W(η⁶-C₇H₈)₂, c] = (242.2 ± 8) for the standard enthalpies of formation at 25°C. The corresponding ΔH^o_f(g) values, using available and estimated enthalpies of sublimation, are (329.9 ± 11) and 352.2 ± 11) respectively, from which the metalligand mean bond-dissociation enthalpies, $\text{D}$(Mo—benzene) = (247.0 ± 6) and $\text{D}$(W—toluene) = (304.0 ± 6) kJ mol^?1, are derived.     

Formation enthalpies of organic oxygen-containing heterocyclic radicals

Enthalpies of formation (Δ _f H ^o) of 57 oxygen-containing heterocyclic radicals have been determined from literature values of the dissociation energies of C–H chemical bonds in appropriate molecules. Within the framework of a quantitative structure–property correlation based on the additive-group model, an analysis has been carried out of the obtained Δ _f H ^o values, the reliability of these data has been shown, and a set of values has been determined of the cyclic stress of the radicals being considered. The parameters of the additive-group method are recommended for the calculation of Δ _f H ^o for radicals of the considered class.     

Enthalpies of formation of solid cobalt-tellurium alloys

The enthalpies of formation of solid Co?Te alloys were determined at room temperature with an isoperibol solution calorimeter of the submarine type. Co?Te alloys and mechanical mixtures of the pure components were dissolved in separate experiments in a saturated hydrochloric acid (8.000n)—bromine mixture and the enthalpies of formation obtained by difference. For the NiAs-type β-phase ΔH _f ^o(N_Te)=(4.079–15.017N _Te) kcal·g-atom^?1 and for the marcasitetype γ-phase ΔH _f ^o(N _Te)=(3.787–14.400N _Te) kcal·g-atom^?1. Combining these results with data from the literature integral thermodynamic properties of solid Co—Te alloys were calculated at room temperature and at 600°C.     

Thermochemical properties of free radicals from G3MP2B3 calculations

For a set of 32 selected free radicals, energy minimum structures, harmonic vibrational wave numbers ω_e, principal moments of inertia I_A, I_B, and I_C, heat capacities C°_p(T), entropies S°(T), thermal energy contents H°(T) ? H°(0), and standard enthalpies of formation Δ_fH°(T) were calculated at the G3MP2B3 level of theory in the temperature range 200–3000 K. In this article, thermodynamic functions at T = 298.15 K are presented and compared with recent experimental values. The mean absolute deviation between calculated and experimental Δ_fH°(298.15) values resulted in 3.91 kJ mol^?1, which is close to the average experimental uncertainty of ± 3.55 kJ mol^?1. The influence of hindered rotation on thermodynamic functions is studied for isopropyl and tert‐butyl radicals. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 550–560, 2002     

Thermochemical properties from ab initio calculations: π- and σ-Free radicals of importance in soot formation: •C3H3 (propargyl), •C4H3, •C13H9 (phenalenyl), •C6H5 (phenyl), •C10H7 (naphthyl), •C14H9 (anthryl), •C14H9 (phenanthryl), •C16H9 (pyrenyl), •C12H7 (acenaphthyl), and •C12H9 (biphenylyl)

The calculated difference in the standard heat of formation Δ Δ_fH°(298.15) of n- and i-C₄H₃^• free radicals is 37.9 kJ mol⁻¹ for G3MP2B3 and 45.0 kJ mol⁻¹ for CCSD(T)-CBS (W1U) calculations, which seems to preclude the direct even-carbon radical pathway to benzene and higher PAH (polycyclic aromatic hydrocarbon) formation including soot in a hydrocarbon flame. For the phenyl-type σ-radicals listed in the title, absolute values of Δ_fH°(298.15) have been calculated using G3MP2B3-computed values of bond dissociation energies D°(298.15) and combined with experimental values of Δ_fH° (298.15) for the parent hydrocarbon because of a slight systematic overprediction of the thermodynamic stability of large PAHs by the applied computational G3MP2B3 method. Standard enthalpies of formation Δ_fH°(298.15) as well as absolute entropies S° and heat capacities C°_p are given for a series of π- and σ-free radicals important to combustion as a function of temperature. A spread of roughly 40 kJ mol⁻¹ in the average C H bond strength of PAH leading to σ-radicals has been calculated, the lowest leading to 4-phenanthryl (463.6 kJ mol⁻¹), the highest leading to 2-biphenylyl radical (502.5 kJ mol⁻¹). © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 395–415, 2008     

Collisionally activated dissociation of 2,4,6-triphenylpyridinium cations

Thresholds for the appearance of fragment ions allowed the estimation of threshold fragmentation energies (TFE) for the collisionally activated dissociation (CAD) in the gas phase of laser-desorbed pyridine-ring substituted N-benzylpyridinium cations to form pyridine and a carbocation. p-Methylbenzylpyridinium cation underwent an alternative CAD into pyridinium cation and the p-quinodimethane. The TFE are discussed in comparison with the energy differences (ΔΔH_f = ΔH_f(Py) + ΔH_f(R⁺) ? ΔH_f(Py ⁺R) calculated by the AM1 method to provide strong evidence for benzyl to tropylium cation rearrangement in an ion-molecule pair.     

Ionic solvation in water + co-solvent mixtures. Part 8. Total free energies of transfer and free energies of transfer with the “neutral” component removed of single ions from water into water + acetone

The acid dissociation constants of a wide range of acids in water+acetone mixtures have been combined with values for the free energy of transfer of the proton. ΔG⁰_t(H⁺ to calculate values for the free energy of transfer of ions which derive only from the charge on the ion. ΔG⁰_t(i)_c. As the values of ΔG⁰_t(H⁺) have been revised, revised values for the total free energies of transfer of cations and anions, ΔG⁰_t(M⁺) and ΔG^o_t(X^-), are given. New data for ΔG^o_t(MX_n) is also split into values for ΔG⁰_t(Mⁿ⁺) (where n=1 and 2) and ΔG⁰_t(X^?). These free energies of transfer, both total and those deriving from the charge alone, are compared with similar free energies in other mixtures water+co-solvent. Values for ΔG^o_t(i)_c do not conform to a Born-type relationship and show the importance of structural effects in the solvent even when only the transfer of the charge is involved.     

Thermal decomposition of zinc and cadmium zirconyl oxalates

The enthalpy of formation at 298.15 K of the polymer Al₁₃O₄(OH)₂₈(H₂O)³⁺₈ and an amorphous aluminium trihydroxide gel was studied using an original differential calorimetric method, already developed for adsorption experiments, and aluminium-27 NMR spectroscopy data. ΔH_f “Al₁₃” (298.15 K) = ? 602 ± 60.2 kJ mole^?1 and ΔH_f Al(OH)₃ (298.15 K) = ? 51 ± 5 kJ mole^?1. Using theoretical values of ΔG_R “Al₁₃” and ΔG_R Al(OH)₃, we calculated ΔG_f “Al₁₃” (298.15 K) = ? 13282 kJ mole^?1; ΔS_f “Al₁₃” (298.15 K) = + 42.2 kJ mole^?1; ΔG_f Al(OH)₃ (298.15 K) = ? 782.5 kJ mole^?1; and ΔS_f Al(OH)₃ (298.15 K) = + 2.4 kJ mole^?1.     

Bond dissociation energies and radical heats of formation in CH3Cl,CH2Cl2, CH3Br,CH2Br2, CH2FCl,and CHFCl2

An analysis of thermochemical and kinetic data on the bromination of the halomethanes CH_4–nX_n (X = F, Cl, Br; n = 1–3), the two chlorofluoromethanes, CH₂FCl and CHFCl₂, and CH₄, shows that the recently reported heats of formation of the radicals CH₂Cl, CHCl₂, CHBr₂, and CFCl₂, and the C? H bond dissociation energies in the matching halomethanes are not compatible with the activation energies for the corresponding reverse reactions. From the observed trends in CH₄ and the other halomethanes, the following revised ΔH°_f,298 (R) values have been derived: ΔH°_f(CH₂Cl) = 29.1 ± 1.0, ΔH°_f(CHCl₂) = 23.5 ± 1.2, ΔH_f(CH₂Br) = 40.4 ± 1.0, ΔH°_f(CHBr₂) = 45.0 ± 2.2, and ΔH°_f(CFCl₂) = ?21.3 ± 2.4 kcal mol^?1. The previously unavailable radical heat of formation, ΔH°_f(CHFCl) = ?14.5 ± 2.4 kcal mol^?1 has also been deduced. These values are used with the heats of formation of the parent compounds from the literature to evaluate C? H and C? X bond dissociation energies in CH₃Cl, CH₂Cl₂, CH₃Br, CH₂Br₂, CH₂FCl, and CHFCl₂.     

The standard thermodynamic properties of 4<Emphasis Type="Italic">f</Emphasis> metal trichlorides

The enthalpies of sublimation Δ_sub H ⁰(298) of 4f metal trichlorides were calculated by the second and third laws of thermodynamics from saturated vapor pressures using the thermodynamic functions of the condensed and gaseous states suggested by us. The set of the Δ_sub H ^o(298) enthalpies was analyzed to determine the most reliable values. The enthalpies of atomization found from these values were compared with those calculated from the measured equilibrium constants of gas phase reactions with the participation of the compounds under consideration and the enthalpies of atomization found from the experimental appearance potentials AP(Ln⁺/LnCl₃). Recommended Δ_at H ^o(298) values were obtained for all the 4f metal trichlorides.     

The enthalpies of formation of CH3Mn(CO)5 and of CH3Re(CO)5, and the strengths of the CH3Mn and CH3Re bonds

From measurements of the heats of iodination of CH₃Mn(CO)₅ and CH₃Re(CO)₅ at elevated temperatures using the ‘drop’ microcalorimeter method, values were determined for the standard enthalpies of formation at 25° of the crystalline compounds: ΔH^o_f[CH₃Mn(CO)₅, c] = ?189.0 ± 2 kcal mol^?1 (?790.8 ± 8 kJ mol^?1), ΔH^o_f[Ch₃Re(CO)₅,c] = ?198.0 ± kcal mol^?1 (?828.4 ± 8 kJ mo^?1). In conjunction with available enthalpies of sublimation, and with literature values for the dissociation energies of MnMn and ReRe bonds in Mn₂(CO)₁₀ and Re₂(CO)₁₀, values are derived for the dissociation energies: D(CH₃Mn(CO)₅) = 27.9 ± 2.3 or 30.9 ± 2.3 kcal mol^?1 and D(CH₃Re(CO)₅) = 53.2 ± 2.5 kcal mol^?1. In general, irrespective of the value accepted for D(MM) in M₂(CO)₁₀, the present results require that, D(CH₃Mn) = $\text{1}\text{2}$D(MnMn) + 18.5 kcal mol^?1 and D(CH₃Re) = $\text{1}\text{2}$D(ReRe) + 30.8 kcal mol^?1.     

Die Bildungsenthalpie von SnJ4

The changes of enthalpy for the reactions

1. Sn(c)+2I₂(c)+4165 CS₂(l)=[SnI₄; 4165 CS₂] (sol.),
2. SnI₄(c)+4223 CS₂(l)=[SnI₄; 4223 CS₂] (sol.)

At 298,15 K have been found by solution calorimetry to be ΔH ₁=(?46.7±0.3) and ΔH ₂=(+3.2±0.1) kcal Mol^?1, resp. Neglecting the heat of dilution which is approximately zero these values give ΔH _f ^o (SnI₄; c; 298 K)=9?49.9±0.4) kcal Mol^?1 for the enthalpy of formation of SnI₄. From existing literature data the standard entropy is calculated to beS ^o(SnI₄; c; 298 K)=69,7 cal Mol^?1 K^?1 giving ΔG _f ^o (SnI₄; c; 298 K)=?50,5 kcal Mol^?1 for the corresponding change in theGibbs free energy.     

The determination of enthalpies of formation of organic free radicals from bond dissociation energies. 5. Organosulfur radicals

The formation enthalpies (H _f°) of 12 organosulfur radicals (R^·) were determined for the first time from the published values of dissociation energies of R—X bonds.