Determination of enthalpies of formation of organic free radicals from bond dissociation energies 1. Hydrocarbon radicals

Orlov, Yu. D.; Zaripov, R. Kh.; Lebedev, Yu. A.

doi:10.1007/bf02495964

Cited by 6 publications

(7 citation statements)

References 13 publications

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“…In the latter case the results obtained are in close agreement with experimental 5, 7 and evaluation values 6. Hence, the proposed approach gives a reasonable description of thermochemical characteristics for both neutral conjugated compounds and radicals.…”

Section: Direct Calculation Of Heat Of Formationsupporting

confidence: 84%

“…Only their accuracy mattered. In this connection it should be noted that direct calculation gives rise to somewhat higher value of heat of formation for 2,3‐benzofluorenyl in comparison with its evaluation value 6 (see Table I). This appears to be due to the fact that experimental heat of formation of tetracene, considered unreliable by many researchers 14, 18, was used in macroincrements‐based estimation of Δ H

_{0}^{italicf}

values for initial 2,3‐benzofluorene molecules.…”

Section: Additive‐superpositional Approach For Calculation Of Thermocmentioning

confidence: 85%

“…Thus, for instance, introduction of methyl group into pyridine and thiophene molecules gives rise to the following equation for changes in their heats of formation 22: For alternant systems, where all residual π‐electronic charges can be taken as zero, effects of the chemical substitution in accordance with correlation relationship (17) must be described by an additive model. Indeed, the heats of formation thus calculated and determined from experiments 5, 6 (unbracketed and bracketed, respectively) both for neutral molecules—toluene 11.5 (11.9), methylnaphthalenes 27.8 (1‐Me–27.9; 2‐Me–27.8), dimethylnaphthalenes 19.5 (19.6 ÷ 20.0)—and radical species—methylallylic 30.8 (1‐Me–30.0; 2‐Me–29.7), dimethylallylic 22.5 (22.0 ÷ 22.4), trimethylallylic 14.2 (9.0 ÷ 9.5), methylbenzylic 39.5 (o‐Me, M ‐Me, p‐Me–39.8, α‐Me–40.4), and dimethylbenzylic 31.5 (31.1 ÷ 33.2) (all in kcal/mol)—are in good agreement.…”

Section: Effects Of Chemical Substitution On Heats Of Formation Of Comentioning

confidence: 99%

“…Thermochemical data on conjugated hydrocarbon radicals formed, for example, in aging, thermodestruction and photodestruction of polymeric materials (polyvinyl chloride) 1, and in pyrolysis of coal 2 and hydrocarbons 3 are of interest, owing to their practical importance and scientific merit. Unfortunately, experimental heats of formation for free radicals involving the system of conjugated bonds are few in number because of their enhanced reactivity; the majority of these data can be found in reviews 4–7. Moreover, these data were obtained by different methods depending on the experimental techniques developed at different times, many of the radicals were studied 30 years ago.…”

Section: Introductionmentioning

confidence: 99%

“…The work covers 30 structurally different conjugated hydrocarbon radicals: polyene 1–4 , monocyclic 5–7 and polycyclic alternant 8–19 and nonalternant 20–27 , and phenylmethyl 28–30 radicals (see Scheme ). The calculated thermochemical properties of these radicals will be compared with the experimental data and those obtained using the group‐equivalent method 5–7, 24.…”

Section: Introductionmentioning

confidence: 99%

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Calculation of thermochemical properties of conjugated radicals

Vysotsky

Bryantsev

2003

Int J of Quantum Chemistry

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ABSTRACT:Heat of formation for 30 conjugated hydrocarbon radicals were calculated within the framework of an unrestricted Hartree-Fock method using the same set of -Hamiltonian parameters for systems with closed and open electronic shell. Based on -electronic perturbation theory, the model of aromatic annelation and radical CH 2 substitution of neutral molecules was developed. The proposed model makes it possible to obtain thermochemical properties of radicals on the basis of calculated or experimental data for less lengthy analogues. Direct calculation and results based on perturbation theory agree closely with each other and with experiment.

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Section: Direct Calculation Of Heat Of Formationsupporting

confidence: 84%

_{0}^{italicf}

values for initial 2,3‐benzofluorene molecules.…”

Section: Additive‐superpositional Approach For Calculation Of Thermocmentioning

confidence: 85%

Section: Effects Of Chemical Substitution On Heats Of Formation Of Comentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Calculation of thermochemical properties of conjugated radicals

Vysotsky

Bryantsev

2003

Int J of Quantum Chemistry

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Enthalpies of formation of alkyl radicals

et al. 2014

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The data on the enthalpies of formation ( f H) for alkyl radicals (R • ) were examined. Taking into account the values of enthalpies of С-Х bond dissociation (Х = Н, Cl) in alkanes and their monochlorosubstituted derivatives,  f H of fifteen R • were determined for the first time. The values of  f H(R • ) were analyzed on the basis of quantitative structure-property relationships in terms of the additive groups model with the new extended set of fragments introduced according to the quantum theory "Atoms in Molecule." The parameters for predic tion of  f H of radicals for of the considered class were determined. The renewed and extended by more than 25% database on  f H of alkyl radicals was proposed.Key words: free radicals, alkyl radicals, enthalpy of formation, enthalpy of bond disso ciation, quantitative structure-property relationships, additive groups model. Data on enthalpies of formation ( f H at 298.15 K and 0.1 MPa) of alkyl radicals (R • ) are key data in the ther mochemistry of organic free radicals. As a rule, various calculation methods for prediction of  f H(R • ) are ap proved on the basis of these values. They also represent a necessary attribute of reference sets for the calibration of the corresponding correlations of quantitative structureproperty relationships (QSPR). On the basis of them, correlations of chemical bonds in organic compounds are determined. These data are also important for studying processes of hydrocarbon transformations involving R • .Alkyl radicals R • were almost the first organic inter mediates characterized 1-3 by  f H, and a range of values were disputed for a long time, 4,5 due to which the re searchers concluded that the initial values of  f H for CH 3 C • H 2 , CH 3 CH 2 C • H 2 , (CH 3 ) 2 C • Н, and (CH 3 ) 3 C • should be increased by 10-16 kJ mol -1 . The NIST data base presently contains 6 the values of  f H for eight alkyls, of which only one, for the initial member of the series ( f H(С • Н 3 ) = 146.7±0.3 kJ mol -1 ), was established 7 by IUPAC. According to literature data, 8,9  f H are known for 20 alkyl radicals; the corresponding values are present ed for 24 compounds 10 ; and  f H for 26 compounds are given. 11 These values were presented 8,9 without any analy sis and there is a contradiction between them and pub lished 10 values, since the authors 10 used earlier, underesti mated values for the indicated above members of the ho mological series. It should be mentioned that these values were qualified 10 as "doubtful" with errors ranging from 8 to 13 kJ mol -1 . According to published data, 8,9,11 the errors of the discussed values do not exceed 2-4 kJ mol -1 ; however, in our opinion, the real values of these errors are not lower than 4-6 kJ mol -1 (except for that for radi cal • СН 3 ).An analysis of the enthalpies (energies) of С-X bond (Х = H, Cl) dissociation (D) in alkanes (RH) and mono chloroalkanes showed that the values of  f H(R • ) can be determined on the basis of D for a series of earlier un studied alkyl R • . T...

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Thermochemical Data and Additivity Group Values for Ten Species of o-Xylene Low-Temperature Oxidation Mechanism

Canneaux¹,

Vandeputte²,

Hammaecher

et al. 2011

J. Phys. Chem. A

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o-Xylene could be a good candidate to represent the family of aromatic hydrocarbons in a surrogate fuel. This study uses computational chemistry to calculate standard enthalpies of formation at 298 K, Δ(f)H°(298 K), standard entropies at 298 K, S°(298 K), and standard heat capacities C(p)°(T) over the temperature range 300 K to 1500 K for ten target species present in the low-temperature oxidation mechanism of o-xylene: o-xylene (1), 2-methylbenzyl radical (2), 2-methylbenzylperoxy radical (3), 2-methylbenzyl hydroperoxide (4), 2-(hydroperoxymethyl)benzyl radical (5), 2-(hydroperoxymethyl)benzaldehyde (6), 1-ethyl-2-methylbenzene (7), 2,3-dimethylphenol (8), 2-hydroxybenzaldehyde (9), and 3-hydroxybenzaldehyde (10). Δ(f)H°(298 K) values are weighted averages across the values calculated using five isodesmic reactions and five composite calculation methods: CBS-QB3, G3B3, G3MP2, G3, and G4. The uncertainty in Δ(f)H°(298 K) is also evaluated. S°(298 K) and C(p)°(T) values are calculated at B3LYP/6-311G(d,p) level of theory from molecular properties and statistical thermodynamics through evaluation of translational, rotational, vibrational, and electronic partition functions. S°(298 K) and C(p)°(300 K) values are evaluated using the rigid-rotor-harmonic-oscillator model. C(p)°(T) values at T ≥ 400 K are calculated by treating separately internal rotation contributions and translational, external rotational, vibrational, and electronic contributions. The thermochemical properties of six target species are used to develop six new additivity groups taking into account the interaction between two substituents in ortho (ORT/CH2OOH/ME, ORT/ET/ME, ORT/CHO/OH, ORT/CHO/CH2OOH) or meta (MET/CHO/OH) positions, and the interaction between three substituents (ME/ME/OH123) located one beside the other (positions numbered 1, 2, 3) for two- or three-substituted benzenic species. Two other additivity groups are also developed using the thermochemical properties of benzenic species taken from the literature: the C/CB/H2/OO and the CB/CO groups. These groups extend the capacities of the group additivity method to deal with substituted benzenic species.

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Determination of enthalpies of formation of organic free radicals from bond dissociation energies 1. Hydrocarbon radicals

Cited by 6 publications

References 13 publications

Calculation of thermochemical properties of conjugated radicals

Calculation of thermochemical properties of conjugated radicals

Enthalpies of formation of alkyl radicals

Thermochemical Data and Additivity Group Values for Ten Species of o-Xylene Low-Temperature Oxidation Mechanism

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