Quantum chemical metabolism‐based simulation of carcinogenic potency of benzene derivatives

Using an oxenoid model, we investigated dependences of carcinogenic potency of the benzenes C₆H₅‐X on a nature of substituents X. According to the model, a P450 enzyme breaks a dioxygen molecule and generates the oxens, which readily react with substrates. We suggest that a stability of the intermediate OC₆H₆‐X with tetrahedrally coordinated C atom relative to the molecule C₆H₅‐X determines a rate of substrate biotransformation. Using MO LCAO MNDO approach, we calculated the total energies of molecules C₆H₆‐X and arene oxides OC₆H₆‐X. A difference ΔE_min of these values determines activation energy of oxidation reaction. The compounds with the low ΔE_min values are noncarcinogenic. Benzene derivatives with high ΔE_min values belong to carcinogenic compounds series. The carcinogenicity of amino‐ and nitro‐substituted benzenes is also determined by N‐oxidation of amino and reduction of the nitro group. As the phenylhydroxylamines XC₆H₄NHOH and nitrenium ions XC₆OH₄NH⁺ are the common metabolites of the nitro‐ and amino‐substituted benzenes and nitrenium ions XC₆H₄NH⁺ are the ultimate carcinogens, we use the differences ΔE_N = E(XC₆H₄NH⁺) ? E(XC₆H₄NHOH) as the second parameter characterizing the carcinogenic activity of amino‐ and nitro‐substituted benzenes. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Sequential segregation of Sn and Sb in a Cu(111) single crystal

The sequential segregation of Sn and Sb to the surface of a Cu(111) single crystal was measured in the temperature range 400–1100 K by Auger electron spectroscopy. It was found that Sn with the higher diffusion coefficient first segregates to the surface and then is replaced by the slower‐segregating Sb. The results were fitted by a ternary segregation model yielding segregation energies (ΔG_Sn = 76.3 kJ mol^?1, ΔG_Sb = 95.9 kJ mol^?1), interaction parameters (Ω_SnCu = 3.8 kJ mol^?1, Ω_SbCu = 16.2 kJ mol^?1, Ω_SnSb = ?5.3 kJ mol^?1) and diffusion coefficients (D_0(Sn) = 1.8 × 10^?5 m² s^?1, E_Sn = 173 kJ mol^?1, D_0(Sb) = 6.0 × 10^?5 m² s^?1, E_Sb = 205 kJ mol^?1) for both species. The validity of the interaction coefficients and segregation energies was verified using the Guttman equations for equilibrium segregation in ternary systems. Copyright © 2003 John Wiley & Sons, Ltd.     

Thermal degradation of polyisobutylene studied using factor-jump thermogravimetry

The overall activation energy of the thermal degradation of polyisobutylene has been measured using factor-jump thermogravimetry to be 206±1 kJ/mole over the range 365 to 405° in N₂ at 800 mm Hg pressure and flowing at 4 mm/s over the sample. This is consistent with some values reported for thermal degradation in vacuum and in solution. In 5 mm Hg of N₂, an apparent activation energy of 218±2 kJ/mole was found, and in vacuum the apparent activation energy is 238±13 kJ/mole. Troublesome bubbling made the vacuum values difficult to measure. Substitution of reasonable values for the activation energies of initiation,E _i , termination,E _t , and the activation energy,E _a , for vacuum degradation in the equationE _a =E _i /2E _d -E _t /2 yields an activation energy E_d=84 kJ/mole for the unzipping reaction. This equation presupposes a degradation mechanism of random initiation, unzipping, and bimolecular termination. Substitution of reasonable values for the heat of polymerization, ΔH, in the definition ΔH=E _p ?e _d suggests that the activation energy of the polymerization reaction at 375° is approximately 30 kJ/mole.     

Pyrolysis of 2-phenylethylamines heats of formation of aminomethyl radicals R2NCH2 · (R = H,CH3)

A kinetic study of the very low-pressure pyrolysis of ethylbenzene (I), 2-phenylethylamine (II), and N,N-dimethyl 2-phenylethylamine (III) above 900 K yields the heats of formation of aminomethyl (A) and N,N-dimethylaminomethyl (B) radicals: ΔH_{?, 300 K}(A) = 30.3 and ΔH_{?, 300 K}(B) = 27.5 kcal/mol. The difference of stabilization energies E_s, (relative to methyl radicals): Δ = E_s(B) ? E_s(A) = (2 ± 1) kcal/mol, conforms to similar effects in methyl substituted alkyl and amino free radicals.     

s-四嗪-水簇复合物的理论研究

用量子化学B3LYP方法和6-31＋＋G**基函数研究了s-四嗪-水簇复合物基态分子间相互作用, 并进行了构型优化和频率计算, 分别得到无虚频稳定的s-四嗪-(水)₂复合物、s-四嗪-(水)₃复合物和s-四嗪-(水)₄复合物6个、9个和12个. 复合物存在较强的氢键作用, 复合物结构中形成一个N…H—O氢键并终止于O…H—C氢键的氢键水链构型最稳定. 经基组重叠误差和零点振动能校正后, 最稳定的1∶2, 1∶3和1∶4(摩尔比)复合物的结合能分别是41.35, 70.9和 94.61 kJ/mol. 振动分析显示氢键的形成使复合物中水分子H—O键对称伸缩振动频率减小(红移). 研究表明N…H键越短, N…H—O键角越接近直线, 稳定化能越大, 氢键作用越强. 同时, 用含时密度泛函理论方法在TD-B3LYP/6-31＋＋G**水平计算了s-四嗪单体及其氢键复合物的第一¹(n, p*)激发态的垂直激发能.     

Kinetics of biodesulfurization of a high-sulfur coal

The apparent activation and deactivation energies and the corresponding frequency factors of coal desulfurization byThiobacillus ferrooxidans have been determined to be ΔE _a = 60.9 kJ,A _a = 1.45 s^-1 and ΔE_d = 178.3 kJ,A _d = 5.65×10²⁷ s^-1, respectively. The thermo-dynamic values (AG^?, ΔH ^?, and ΔS^?) of the activated complex were calculated. Kinetic parameters of the Monod equation were determined to beV _m = 55.9 mg dm^-3 h^-1 andK = 24.1% pulp density. The maximum rate of desulfurization of coal was found to beV _m = 55.7 mg dm^-3 h^-1 for the particle size. The generalized second order regression equation relating the yield of desulfurization to the leaching parameters was shown to adequately predict coal extraction data and optimum values of process variables. Tank leaching studies using optimum conditions resulted coal desulfurization about 90%. The iron hydrolysis reactions involving the formation of mono- and poly-nuclear, hydroxo- and sulfato complexes of amorphous and crystalline precipitates were discussed.     

Correlation of activation energies of radical–molecule metathesis reactions with enthalpic,polar, and steric parameters

It is shown that the activation energies E oF chlorine atom abstraction by cyclohexyl radicals and hydrogen atom abstraction by Cl atoms from polychloroalkanes can be correlated with the bond dissociation energies D and the Taft polar and steric substituent constants σ* and E_s by the expression: where ΔE and ΔD represent the differences between the E and D values of a given substrate and those of a reference compound (CH₃ substituted substrate) and α, ρ, and δ are the corresponding correlation coefficients. The use of this expression allows quantitative evaluation of the relative contribution of the various factors affecting the activation energies of these reactions and estimation of related thermochemical data.     

Propagation rate coefficients of isobornyl acrylate,tert‐butyl acrylate and 1‐ethoxyethyl acrylate: A high frequency PLP‐SEC study

Pulsed laser polymerization (PLP) coupled to size exclusion chromatography (SEC) is considered to be the most accurate and reliable technique for the determination of absolute propagation rate coefficients, k_p. Herein, k_p data as a function of temperature were determined via PLP‐SEC for three acrylate monomers that are of particular synthetic interest (e.g., for the generation of amphiphilic block copolymers). The high‐T_g monomer isobornyl acrylate (iBoA) as well as the precursor monomers for the synthesis of hydrophilic poly(acrylic acid), tert‐butyl acrylate (tBuA), and 1‐ethoxyethyl acrylate (EEA) were investigated with respect to their propagation rate coefficient in a wide temperature range. By application of a 500 Hz laser repetition rate, data could be obtained up to a temperature of 80 °C. To arrive at absolute values for k_p, the Mark‐Houwink parameters of the polymers have been determined via on‐line light scattering and viscosimetry measurements. These read: K = 5.00 × 10⁵ dL g⁻¹, a = 0.75 (piBoA), K = 19.7 × 10⁵ dL g⁻¹, a = 0.66 (ptBA) and K = 1.53 × 10⁵ dL g⁻¹, a = 0.85 (pEEA). The bulky iBoA monomer shows the lowest propagation rate coefficient among the three monomers, while EEA is the fastest. The activation energies and Arrhenius factors read: (iBoA): log(A/L mol⁻¹ s⁻¹) = 7.05 and E_A = 17.0 kJ mol⁻¹; (tBuA): log(A/L mol⁻¹ s⁻¹) = 7.28 and E_A = 17.5 kJ mol⁻¹ and (EEA): log(A/L mol⁻¹ s⁻¹) = 6.80 and E_A = 13.8 kJ mol⁻¹. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6641–6654, 2009     

A theoretical study of electronic effects in alkyne‐linked reactive intermediates: (nitrenoethynyl)methylenes, (nitrenoethynyl)silylenes,and (nitrenoethynyl)germylenes

Acetylene‐linked reactive intermediates of (nitrenoethynyl)‐X‐methylenes, (nitrenoethynyl)‐X‐silylenes, and (nitrenoethynyl)‐X‐germylenes are almost experimentally unreachable (X–M–C≡C–N; X=H ( 1 ), CN ( 2 ), OH ( 3 ), NH₂ ( 4 ), NO₂ ( 5 ), and CHO ( 6 ); M=C, Si, and Ge). The effects of the electron‐donating and electron withdrawing groups were compared and contrasted at seven levels of theory. All singlet species as ground states with one local open‐shell singlet carbene subunit (π¹π¹) and another local open‐shell singlet nitrene subunit (π¹π¹) were found to be more stable than their corresponding triplets including one local open‐shell singlet carbene (δ¹π¹) (or one local closed‐shell singlet carbene [δ²π⁰]) and another local triplet nitrene subunit (π¹π¹) with 45.94–77.996 kcal/mol singlet–triplet energy gap (ΔE_s‐t). Their relative silylenes and germylenes made reduction of ΔE_s‐t, so the triplet ground states were found for species 3 _Si , 4 _Si , 5 _Si , 2 _Ge , 3 _Ge , 4 _{Ge ,} and 5 _Ge . All the singlet silylenes/germylenes formed by one local closed‐shell singlet silylenes/germylenes (δ²π⁰) and one local closed‐shell singlet nitrene subunit (π²π⁰). Also, one local closed‐shell singlet silylene/germylene subunit (δ²π⁰) and one local triplet nitrene subunit (π¹π¹) were observed for triplet silylenes/germylenes. The singlet and triplet species 3 _Si , 4 _Si , 3 _Ge , and 4 _Ge , due to their electrophilic (Si₄/Ge₄) and nucleophilic (X₅) centers, could be identified as intermediates in chemical reactions.     

On the correlation between photoelectron and electronic spectra in trans- azomethane

A possibility of correlating electronic and photoelectron spectra is discussed, using trans-azomethane as an example. The Coulomb and exchange integrals required were obtained by three semi-empirical SCF-methods: MINDO/2, CNDO/2, and a modified CNDO method. The orbital energies were taken as minus the corresponding experimental ionization potentials. The sequence of the transition energies ΔE (n_s → π*) Δ E (n_a → π*) < ΔE (π → π*) is found to be different from the ionization potential sequence IP (n_s) < IP (π) < IP (n_a), in agreement with previous spectroscopic studies; the results support the latest view that the π → π* transition of the azo group occurs at around 12 eV.     

Volumetric Properties for the Electrolyte (NaCl,NaBr and NaI) Monosaccharide (D‐Mannose and D‐Ribose)‐Water Systems at 298.15 K

Densities have been measured for the electrolyte (NaCl, NaBr and NaI)‐monosaccharide (D ‐mannose and D‐ribose)‐water solutions at 298.15 K. These data have been used to calculate the apparent molar volumes of the saccharides (V_Φ,S) and electrolytes (V_Φ,E) in the studied solutions. Infinite dilution apparent molar volumes, V_Φ,S⁰ and V_Φ,E⁰, have been evaluated, together with the standard transfer volumes of the saccharides (Δ_tV_S⁰) from water to aqueous electrolyte solutions and those of the electrolytes (Δ_tV_E⁰) from water to aqueous saccharide solutions. It was shown that both the Δ_tV_S⁰ and Δ_tV_E⁰ values are positive and increase with increasing molalities of sodium halides and saccharides, respectively. Overall, the Δ_tV_S⁰ and Δ_tV_E⁰ values have the order of NaCl > NaBr > NaI except for NaI‐ribose and NaI‐ribose. Volumetric interaction parameters for the electrolyte‐monosaccharide pairs in water were obtained and interpreted by the stereochemistry of the monosaccharide molecules and the structural interaction model.     

Theoretical investigation on identical anionic halide‐exchange SN2 reaction processes on N‐haloammonium cation NH3X+ (X = F,Cl, Br,and I)

CCSD(T) calculations have been used for identically nucleophilic substitution reactions on N‐haloammonium cation, X^? + NH₃X⁺ (X = F, Cl, Br, and I), with comparison of classic anionic S_N2 reactions, X^? + CH₃X. The described S_N2 reactions are characterized to a double curve potential, and separated charged reactants proceed to form transition state through a stronger complexation and a charge neutralization process. For title reactions X^? + NH₃X⁺, charge distributions, geometries, energy barriers, and their correlations have been investigated. Central barriers ΔE for X^? + NH₃X⁺ are found to be lower and lie within a relatively narrow range, decreasing in the following order: Cl (21.1 kJ/mol) > F (19.7 kJ/mol) > Br (10.9 kJ/mol) > I (9.1 kJ/mol). The overall barriers ΔE relative to the reactants are negative for all halogens: ?626.0 kJ/mol (F), ?494.1 kJ/mol (Cl), ?484.9 kJ/mol (Br), and ?458.5 kJ/mol (I). Stability energies of the ion–ion complexes ΔE_comp decrease in the order F (645.6 kJ/mol) > Cl (515.2 kJ/mol) > Br (495.8 kJ/mol) > I (467.6 kJ/mol), and are found to correlate well with halogen Mulliken electronegativities (R² = 0.972) and proton affinity of halogen anions X^? (R² = 0.996). Based on polarizable continuum model, solvent effects have investigated, which indicates solvents, especially polar and protic solvents lower the complexation energy dramatically, due to dually solvated reactant ions, and even character of double well potential in reactions X^? + CH₃X has disappeared. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

A generalized formula for the energies of alternant molecular orbitals. II. Heteronuclear molecules

Using the method of alternant molecular orbitals (AMO ), it is shown that the energies of AMOS (E_kσ) for an arbitrary heteronuclear alternant system, having a singlet ground state, are connected with the energies of MOS (e_{k(k )}) obtained by means of the conventional Hartree–Fock (HF ) method (SCF -LCAO -MO -PPP ) via the formula: In the general case, the determination of the correlation corrections δ_i,kσ is connected with the solving of a complicated system of integral equations, which is considerably simplified if the Hubbard approximation is accepted for the electron interaction. The energy spectrum of a chain with two atoms in the elementary cell (AB)_n is considered as an example. It is shown that if nontrivial solutions exist (δ_i,kσ ≠ 0), the correlation correction for AMOS of different spin are different (δ_i,kσ ≠ δ_i,kβ), from which it follows, that the width of the energy gap ΔE_∞ for AMOS with different spin is different: ΔE_∞,α ≠ ΔE_∞,β.     

Density functional theory calculation of 2p spectra of SiH4, PH3, H2S,HCl, and Ar

The method developed recently for prediction of 1s electron spectra is now extended to the 2p spectra of SiH₄, PH₃, H₂S, HCl, and Ar. The method for X‐ray absorption spectra involves the use of ΔE for the excitation and ionization energies, and application of time‐dependent density functional theory using the exchange‐correlation potential known as statistical average of orbital potentials for the intensities. Additional assumptions and approximations are also made. The best exchange‐correlation functional E_xc for the earlier calculation of ΔE in 1s spectra of C to Ne (namely Perdew–Wang 1986 exchange, combined with Perdew–Wang 1991 correlation) is no longer used in this work on 2p spectra of Si to Ar. Instead, recently tested E_xc good for 2p core‐electron binding energies (known as OPTX) for exchange and LYP for correlation, plus scalar zeroth‐order regular approximation is adopted here for the ΔE calculations. Our calculated X‐ray absorption spectra are generally in good agreement with experiment. Although the predictions for the higher excitations suffer from basis set difficulties, our procedure should be helpful in the interpretation of absorption spectra of 2p electrons of Si to Ar. In addition, we report calculated results for other kinds of electron spectra for SiH₄, PH₃, H₂S, HCl, and Ar, including valence electron ionizations and excitations as well as X‐ray emission. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Refined ab initio 6-31G split-valence basis set optimization of the molecular structures of biphenyl in twisted,planar, and perpendicular conformations

Improved full ab initio optimizations of the molecular structure of biphenyl in twisted minimum energy, coplanar, and perpendicular conformations by use of Poles's GAUSSIAN 82 program have been performed in the 6-31G basis set. These lead to geometries and energies of much higher reliability than our earlier STO-3G results. The torsional angle Φ_min obtained now is 45.41° in close agreement with the recent experimental value of 44.4° ± 1.2°. Calculated CC distances may be converted to experimental ED r_g-values by means of independently determined linear regression correlations with very high statistical confidence, although they agree better with experimental x ray data for coplanar biphenyl without this correction. Calculated intramolecular angles are very similar for both STO-3G and 6-31G basis sets. The calculated torsional energy barrier towards Φ = 90° (ΔE⁹⁰) is 6.76 kJ/mol in close agreement with the experimental-31G value of 6.5 ± 2.0 kJ/mol. For coplanar biphenyl with D_2h-symmetry the calculated torsional energy barrier ΔE⁰ is 13.26 kJ/mol which is surprisingly much higher than the experimental value of 6.0 ± 2.1 kJ/mol. This discrepancy could not be resolved by optimizations assumed for two kinds of distortions of planarity of orthohydrogens from the molecular plane of the coplanar carbon atoms. But for the twisted minimum energy conformation asymmetric bending of ortho-H atoms lead to a torsional angle Φ_min = 44.74° together with a dihedral angle towards ortho-H of 1.22°, and consequently even to an increase of torsional energy barriers to ΔE⁰ = 13.51 and ΔE⁹⁰ = 6.91 kJ/mol.     

Protonation enthalpies in fluorosulfonic acid using ab initio self-consistent reaction field theory

Electrostatic solvation free energies were computed for several small neutral bases and their conjugate acids using a continuum solvation model called the self-consistent isodensity polarizable continuum model (SCIPCM). The solvation energies were computed at the restricted Hartree–Fock (RHF) and second-order Møller–Plesset (MP2) levels of theory, as well as with the Becke3–Lee–Yang–Parr (B3LYP) density functional theory, using the standard 6–31G** Gaussian basis set. The RHF solvation energies are similar to those computed at the correlated MP2 and B3LYP theoretical levels. A model for computing protonation enthalpies for neutral bases in fluorosulfonic acid solvent leads to the equation ΔH(B)=−PA(B)+ΔE_t(BH⁺)−ΔE_t(B)+β, where PA(B) is the gas phase proton affinity for base B, ΔE_t(BH⁺) is the SCIPCM solvation energy for the conjugate acid, and ΔE_t(B) is the solvation energy for the base. A fit to experimental values of ΔH(B) for 10 neutral bases (H₂O, MeOH, Me₂O, H₂S, MeSH, Me₂S, NH₃, MeNH₂, Me₂NH, and PH₃) gives β=238.4±2.9 kcal/mol when ΔΔE_t is computed using the 0.0004 e⋅bohr⁻³ isodensity surface for defining the solute cavity at the RHF/6–31G** level. The model predicts that for carbon monoxide ΔH(CO)=10 kcal/mol. Thus, protonation of CO is endothermic, and the conjugate acid HCO⁺ (formyl cation) behaves as a strong acid in fluorosulfonic acid. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 250–257, 1998     

Kinetics and Mechanism Study of the Substitution Reactions of the Chloride Ligand in Dichloro(5,10,15,20)‐tetraphenyl‐21H,23H‐porphinato)tin(IV) by Organic Bases in Dimethylformamide Solvent

Substitution reactions of a Cl⁻ ligand in [SnCl₂(tpp)] (tpp=5,10,15,20‐tetraphenyl‐21H,23H‐porphinato(2−)) by five organic bases i.e., butylamine (BuNH₂), sec‐butylamine (^sBuNH₂), tert‐butylamine (^tBuNH₂), dibutylamine (Bu₂NH), and tributylamine (Bu₃N), as entering nucleophile in dimethylformamide at I=0.1M (NaNO₃) and 30–55° were studied. The second‐order rate constants for the substitution of a Cl⁻ ligand were found to be (36.86±1.14)⋅10⁻³, (32.91±0.79)⋅10⁻³, (22.21±0.58)⋅10⁻³, (19.09±0.66)⋅10⁻³, and (1.36±0.08)⋅10⁻³ M ⁻¹s⁻¹ at 40° for BuNH₂, ^tBuNH₂, ^sBuNH₂, Bu₂NH, and Bu₃N, respectively. In a temperature‐dependence study, the activation parameters ΔH^≠ and ΔS^≠ for the reaction of [SnCl₂(tpp)] with the organic bases were determined as 38.61±4.79 kJ mol⁻¹ and −150.40±15.46 J K⁻¹mol⁻¹ for BuNH₂, 40.95±4.79 kJ mol⁻¹ and −143.75±15.46 J K⁻¹mol⁻¹ for ^tBuNH₂, 30.88±2.43 kJ mol⁻¹ and −179.00±7.82 J K⁻¹mol⁻¹ for ^sBuNH₂, 26.56±2.97 kJ mol⁻¹ and −194.05±9.39 J K⁻¹mol⁻¹ for Bu₂NH, and 39.37±2.25 kJ mol⁻¹ and −174.68±7.07 J K⁻¹ mol⁻¹ for Bu₃N. From the linear rate dependence on the concentration of the bases, the span of k₂ values, and the large negative values of the activation entropy, an associative (A) mechanism is deduced for the ligand substitution.     

Kinetic modeling of ZnO-rGO catalyzed degradation of methylene blue

Photodegradation of organic pollutants strongly depends on design of metal oxide semiconductor photocatalysts. Graphene, if composited with ZnO, can effectively enhance its photocatalytic performance for the eradication of pollutants from aqueous medium. Here in, ZnO-rGO is reported as highly active catalyst for degradation of methylene blue. A 200-mg/L solution of methylene blue dye was completely degraded within 1 h in comparison to 74% and 56% degradation over ZnO and rGO, respectively. The commonly used mechanisms of heterogeneous catalytic reactions, the Langmuir-Hinshelwood mechanism, and the Eley-Rideal mechanisms, were used to describe the reaction kinetics. The Langmuir-Hinshelwood mechanism was found as more favorable in this study. Apparent activation energy, E_ap, true activation energy, E_T, entropy, ΔS, and enthalpy, ΔH were calculated as 36.2 kJ/mol, 13.1 kJ/mol, 197.5 J/mol, and 23.1 kJ/mol, respectively.     

Diindeno-Fused Dibenzo[a,h]anthracene and Dibenzo[c,l]chrysene: Syntheses,Structural Analyses,and Properties

Diindeno-fused dibenzo[a,h]anthracene 6 and diindeno-fused dibenzo[c,l]chrysene 9 contain the key moieties 1,4-quinodipropene (1,4-QDP) and 2,6-naphthoquinodipropene (2,6-NQDP), respectively, and they both have an open-shell singlet ground state. The latter compound exhibits a strong biradical character and interesting properties, including a low ΔE_T−S (2.44 kcal mol⁻¹), a small HOMO–LUMO gap (1.06 eV), a wide photoabsorption range (250–1172 nm), and a large two-photon absorption cross-section (σ=1342±56 GM). This work verifies that 6 has a slightly larger HOMO–LUMO gap and ΔE_T−S than its helical isomer diindeno[2,1-f:1′,2′-j]picene (DIP), but is a much stronger two-photon absorber, verifying the important effect of geometry on the photophysical properties.     

Chain transfer in ethylene polymerization. V. The effect of temperature

In order to determine the effect of temperature on the chain-transfer reaction in the free-radical polymerization of ethylene, chain-transfer constants were measured for sixteen transfer agents at 130°C and 200°C at 1360 atm. The results were interpreted as ΔE*, the activation energy of the chain-transfer constant. This value is equal to the difference in activation energy between the transfer step (hydrogen abstraction) and the propagation step (addition to the monomer double bond): ΔE* = E_s* ? E_p*. Excellent agreement was found between measured ΔE* values determined at 1360 atm pressure and (E_s* ? E_p*) data for ethyl radical determined in vacuum gas-phase reactions. Apparently, the ethyl radical is a good model for polyethyl radical. The chain-transfer constant of ethylbenzene was found to be insensitive to temperature changes, indicating that E_p* = E_s* for this compound.