Computational Study on the Thermal Decomposition of Phenol‐Type Monolignols

A detailed chemical kinetic model has been developed to theoretically predict the pyrolysis behavior of phenol‐type monolignol compounds (1‐(4‐hydroxyphenyl)prop‐2‐en‐1‐one, HPP; p‐coumaryl alcohol, 3‐hydroxy‐1‐(4‐hydroxyphenyl)propan‐1‐one, HHPP; 1‐(4‐hydroxyphenyl)propane‐1,3‐diol, HPPD) released from the primary heterogeneous pyrolysis of lignin. The possible thermal decomposition pathways involving unimolecular decomposition, H‐addition, and H‐abstraction by H and CH₃ radicals were investigated by comparing the activation energies calculated at the M06–2X/6–311++G(d,p) level of theory. The results indicated that all phenol‐type monolignol compounds convert to phenol by side‐chain cleavage. p‐Coumaryl alcohol decomposes into phenol via the formation of 4‐vinylphenol, whereas HPP, HHPP, and HPPD decompose into phenol via the formation of 4‐hydroxybenzaldehyde. The pyrolytic pathways focusing on the reactivity of the hydroxyl group in HPP and producing cyclopentadiene (cyc‐C₅H₆) were also investigated. The transition state theory (TST) rate constants for all the proposed elementary reaction channels were calculated at the high‐pressure limit in the temperature range of 300–1500 K. The kinetic analysis predicted the two favorable unimolecular decomposition pathways in HPP: the one is the dominant channel below 1000 K to produce cyc‐C₅H₆, and the other is above 1000 K to yield phenol (C₆H₅OH).     

Anharmonic Effect of the Unimolecular Isomerization/Decomposition of Benzyne

The anharmonic and harmonic rate constants were calculated for the unimolecular decomposition of o‐benzyne, the isomerization of o‐benzyne to m‐benzyne, the isomerization of m‐benzyne to p‐benzyne and unimolecular decomposition of p‐benzyne by using the Rice–Ramsperger–Kassel–Marcus (RRKM) theory respectively, in the canonical and microcanonical systems. The geometry and the vibrational frequencies were calculated by MP2 and B3LYP methods with 6‐311G(d,p) basis set and the barrier energies were corrected using CBS‐QB3 theory. The anharmonic effect on the reactions was also examined. Comparison of results for the decompositions of benzyne indicate that both in microcanonical and canonical cases, the anharmonic effect on the decomposition of the o‐C₆H₄ and p‐C₆H₄ are significant, while the anharmonic effect on the two isomerizations are not pronounced.     

Chemistry of Energetically Activated Cumulenes—From Allene (H2CCCH2) to Hexapentaene (H2CCCCCCH2)

During the last decade, experimental and theoretical studies on the unimolecular decomposition of cumulenes (H₂C_nH₂) from propadiene (H₂CCCH₂) to hexapentaene (H₂CCCCCCH₂) have received considerable attention due to the importance of these carbon‐bearing molecules in combustion flames, chemical vapor deposition processes, atmospheric chemistry, and the chemistry of the interstellar medium. Cumulenes and their substituted counterparts also have significant technical potential as elements for molecular machines (nanomechanics), molecular wires (nano‐electronics), nonlinear optics, and molecular sensors. In this review, we present a systematic overview of the stability, formation, and unimolecular decomposition of chemically, photo‐chemically, and thermally activated small to medium‐sized cumulenes in extreme environments. By concentrating on reactions under gas phase thermal conditions (pyrolysis) and on molecular beam experiments conducted under single‐collision conditions (crossed beam and photodissociation studies), a comprehensive picture on the unimolecular decomposition dynamics of cumulenes transpires.     

Anharmonic Effect of the Unimolecular Dissociation of Ethyl Radical

The anharmonic and harmonic rate constants have been calculated for the unimolecular dissociation of ethyl radical using the method proposed by Yao and Lin (YL method) at both B3LYP/6‐311++G** and MP2/6‐311++G** levels. The different rate constants indicate that the results obtained from B3LYP and MP2 method are very close. The anharmonic and tunneling effect of the title reaction has also been examined. The comparison shows that, both in microcanonical and canonical systems, the anharmonic rate constants are higher than those for harmonic cases, especially in the case of high total energies and temperatures, which indicates that anharmonic effect of the unimolecular dissociation of ethyl into C₂H₄ and H is so significant that cannot be neglected. The tunneling effect is very small for the decomposition of C₂H₅ radical.     

A detailed chemical kinetic model for high temperature ethanol oxidation

A detailed chemical kinetic model for ethanol oxidation has been developed and validated against a variety of experimental data sets. Laminar flame speed data (obtained from a constant volume bomb and counterflow twin‐flame), ignition delay data behind a reflected shock wave, and ethanol oxidation product profiles from a jet‐stirred and turbulent flow reactor were used in this computational study. Good agreement was found in modeling of the data sets obtained from the five different experimental systems. The computational results show that high temperature ethanol oxidation exhibits strong sensitivity to the fall‐off kinetics of ethanol decomposition, branching ratio selection for C₂H₅OH + OH ↔ Products, and reactions involving the hydroperoxyl (HO₂) radical. The multichanneled ethanol decomposition process is analyzed by RRKM/Master Equation theory, and the results are compared with those obtained from earlier studies. The ten‐parameter Troe form is used to define the C₂H₅OH(+M) ↔ CH₃ + CH₂OH(+M) rate expression as k^∞ = 5.94E23 T^−1.68 exp(−45880 K/T) (s⁻¹) k^o = 2.88E85 T^−18.9 exp(−55317 K/T) (cm³/mol/sec) F_cent = 0.5 exp(−T/200 K) + 0.5 exp(−T/890 K) + exp(−4600 K/T) and the C₂H₅OH(+M) ↔ C₂H₄ + H₂O(+M) rate expression as k^∞ = 2.79E13 T^0.09 exp(−33284 K/T) (s⁻¹) k^o = 2.57E83 T^−18.85 exp(−43509 K/T) (cm³/mol/sec) F _cent = 0.3 exp(−T/350 K) + 0.7 exp(−T/800 K) + exp(−3800 K/T) with an applied energy transfer per collision value of <ΔE_down> = 500 cm⁻¹. An empirical branching ratio estimation procedure is presented which determines the temperature dependent branching ratios of the three distinct sites of hydrogen abstraction from ethanol. The calculated branching ratios for C₂H₅OH + OH, C₂H₅OH + O, C₂H₅OH + H, and C₂H₅OH + CH₃ are compared to experimental data. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 183–220, 1999     

A Shock Tube and Modeling Study about Anisole Pyrolysis Using Time‐Resolved CO Absorption Measurements

The pyrolysis of anisole (C₆H₅OCH₃) was studied behind reflected shock waves via highly sensitive absorption measurements of CO concentration using a rotational transition in the fundamental vibrational band near 4.7 µm. Time‐resolved CO mole fractions were monitored in shock‐heated C₆H₅OCH₃/Ar mixtures between 1000 and 1270 K at 1.3–1.6 bar. The decomposition of C₆H₅OCH₃ proceeds exclusively via homolytic dissociation, with reaction rate k ₁, forming methyl (CH₃) and phenoxy (C₆H₅O) radicals. The subsequent decomposition of C₆H₅O by ring rearrangement and bond dissociation yields CO. To determine the rate constant k ₂ of C₆H₅O decomposition avoiding secondary reactions, allyl phenyl ether (C₆H₅OC₃H₅) was used as an alternative source for C₆H₅O. Its decomposition was studied between 970 and 1170 K at ∼1.4 bar. The potential‐energy surface of C₆H₅O dissociation has been reevaluated at the G4 level of theory. Rate constants determined from unimolecular rate theory are in good agreement with the present experiments. However, the obtained rates k ₂ = 9.1 × 10¹³ exp(−220.3 kJ mol⁻¹/RT )s⁻¹ are significantly higher than those reported before (factor 6, 2, and 1.5 faster than those data reported by Lin and Lin, J. Phys. Chem . 1986, 90, 425–431; Frank et al., 1994; Carstensen and Dean, 2012, respectively). Good agreement was found between the measured CO concentration profiles and simulations based on the mechanism of Nowakowska et al. after substituting k ₂ by the value obtained from experiments on C₆H₅OC₃H₅ in this work. The bimolecular reaction of C₆H₅O and CH₃ toward cresol was identified as the most important reaction influencing the CO concentration at longer reaction time.     

(Zn1-xMnx)C2O4·2H2O在空气中的热分解动力学研究

用热分析（TG-DTG/DTA）、X射线衍射（XRD）技术和透射电镜（TEM）研究了固态物质Zn_1-xMn_xC₂O₄•2H₂O在空气中热分解的过程。热分析结果表明，Zn_1-xMn_xC₂O₄•2H₂O在空气中分两步分解，其失重率与理论计算失重率相吻合。 XRD和TEM结果表明，Zn_1-xMn_xC₂O₄•2H₂O分解的最终产物为Zn_1-xMn_xO,其颗粒大小约为10-13 nm。在非等温条件下对Zn_1-xMn_xC₂O₄•2H₂O的热分解动力学进行了分析。用Friedman法和Flynn-Wall-Ozawa(FWO)法求取了分解过程的活化能E，并用多元线性回归给出了可能的机理函数。Zn_1-xMn_xC₂O₄•2H₂O两步热分解的活化能分别为155.7513 kJ/mol 和215.9397 kJ/mol。     

Kinetics of isopropanol decomposition and reaction with H atoms from shock tube experiments and rate constant optimization using the method of uncertainty minimization using polynomial chaos expansions (MUM‐PCE)

We have used the single‐pulse shock tube technique with postshock GC/MS product analysis to investigate the mechanism and kinetics of the unimolecular decomposition of isopropanol, a potential biofuel, and of its reaction with H atoms at 918‐1212 K and 183‐484 kPa. Experiments employed dilute mixtures in argon of isopropanol, a radical scavenger, and, for H‐atom studies, two different thermal precursors of H. Without an added H source, isopropanol decomposes in our studies predominantly by molecular dehydration. Added H atoms significantly augment decomposition, mainly by abstraction of the tertiary and primary hydrogens, reactions that, respectively, lead to acetone and propene as stable organic products. Traces of acetaldehyde were observed in some experiments above ≈ 1100 K and establish branching limits for minor decomposition pathways. To quantitatively account for secondary chemistry and optimize rate constants of interest, we employed the method of uncertainty minimization using polynomial chaos expansions (MUM‐PCE) to carry out a unified analysis of all datasets using a chemical model–based originally on JetSurF 2.0. We find: k(isopropanol → propene + H₂O) = 10^{(13.87 ± 0.69)} exp(?(33 099 ± 979) K/ T) s^?1 at 979‐1212 K and 286‐484 kPa, with a factor of two uncertainty (2σ), including systematic errors. For H atom reactions, optimization yields: k(H + isopropanol → H₂ + p‐C₃H₆OH) = 10^{(6.25 ± 0.42)} T^2.54 exp(?(3993 ± 1028) K /T) cm³ mol^?1 s^?1 and k(H + isopropanol → H₂ + t‐C₃H₆OH) = 10^{(5.83 ± 0.37)} T^2.40 exp(?(1507 ± 957) K /T) cm³ mol^?1 s^?1 at 918‐1142 K and 183‐323 kPa. We compare our measured rate constants with estimates used in current combustion models and discuss how hydrocarbon functionalization with an OH group affects H abstraction rates.     

Experimental study of fuel decomposition and hydrocarbon growth processes for practical fuel components in nonpremixed flames: MTBE and related alkyl ethers

Fuel decomposition and hydrocarbon growth processes of methyl tert‐butyl ether (MTBE) and related alkyl ethers have been studied experimentally in soot‐producing nonpremixed flames. Temperature, C1–C12 hydrocarbons, and major species were measured in coflowing methane/air flames whose fuel was separately doped with 5000 ppm of MTBE, n‐butyl methyl ether (NBME), sec‐butyl methyl ether (SBME), ethyl tert‐butyl ether (ETBE), and tert‐amyl methyl ether (TAME; =1,1‐dimethylpropyl methyl ether). The consumption rates of the dopants, several simple kinetic calculations, and the dependence of the observed products on fuel composition indicate that the dominant decomposition process was unimolecular dissociation, not H‐atom abstraction. The dominant dissociations were four‐center elimination of alcohols for the doubly branched ethers (MTBE, ETBE, and TAME) and C? O fission for the linear ether (NBME), while four‐center elimination and C? O fission were comparably important for the singly branched ether (SBME). These dissociations produced alkenes which further reacted to produce alkadienes/alkynes, alkenynes, acetylenic compounds, and aromatics. The dependence of the maximum benzene mole fractions on fuel composition was consistent with benzene formation through reactions of highly‐unsaturated C3 and/or C4 hydrocarbons (C₃H₃, n‐C₄H₃, C₄H₄, n‐C₄H₅, etc.). © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 345–358, 2004     

The decomposition of ethanol vapour by infrared radiation from a pulsed HF-laser

The decomposition of ethanol vapour induced by infrared radiation from a pulsed HF-laser has been studied as a function of pressure. At high pressures, above 10 torr, the main primary processes appear to be:C₂H₅OH → H₂ + CH₃CHO,C₂H₅OH → C₂H₄ + H₂O,C₂H₅OH → CH₃ + CH₂OHin a ratio of 3:2:1 which is independent of pressure. At low pressures the process yielding C₂H₄ and H₂O becomes dominant. The results suggest that the high pressure behaviour involves a “thermal” decomposition with collisional processes dominating, whereas at low pressures the decomposition is due to multiple photon absorption which at the lowest pressures approaches a collision-free unimolecular decomposition.     

The Very low-pressure pyrolysis of 2-phenylethylamine. The enthalpy of formation of the aminomethyl radical

The thermal unimolecular decomposition of 2-phenylethylamine (PhCH₂CH₂NH₂) into benzyl and aminomethyl radicals has been studied under very-low-pressure conditions, and the enthalpy of formation of the aminomethyl radicals, ΔH°_{f, 298K} (H₂NCH₂·) = 37.0 ± 2.0 kcal/mol, has been derived from the kinetic data. This result leads to a value for the C—H bond dissociation energy in methylamine, BDE(H₂NCH₂—H) = 94.6 ± 2.0 kcal/mol, which is about 3.4 kcal/mol lower than in C₂H₆ (98 kcal/mol), indicating a sizable stabilization in α-aminoalkyl radicals.     

Modeling of the elementary gas-phase reaction during chemical vapor deposition of silicon carbide from CH3SiCl3/H2

We established a gas-phase, elementary reaction model for chemical vapor deposition of silicon carbide from methyltrichlorosilane (MTS) and H₂, based on the model developed at Iowa State University (ISU). The ISU model did not reproduce our experimental results, decomposition behavior of MTS in the gas phase in an environment with H₂. Therefore, we made several modifications to the ISU model. Of the reactions included in existing models, 236 were lacking in the ISU model, and thus were added to the model. In addition, we modified the rate constants of the unimolecular reactions and the recombination reactions, which were treated as a high-pressure limit in the ISU model, into pressure-dependent rate expressions based on the previous reports (to yield the ISU+ model), for example, H₂(+M) → H + H(+M), but decomposition behavior remained poorly reproducible. To incorporate the pressure dependencies of unimolecular decomposition rate constants, and to increase the accuracies of these constants, we recalculated the rate constants of five unimolecular decomposition reactions of MTS using the Rice-Ramsperger-Kassel-Marcus method at the CBS-QB3 level. These chemistries were added to the ISU+ model to yield the UT2014 model. The UT2014 model reproduced overall MTS decomposition. From the results of our model, we confirmed that MTS mainly decomposes into CH₃ and SiCl₃ at the temperature around 1000°C as reported in the several studies.     

The pyrolysis of ethane in the presence of nitric oxide

The kinetics of the ethane pyrolysis have been studied at temperatures from 550 to 596°C and with 0 to 62% of added nitric oxide. The rates of production of various products were studied by gas chromatography; ethylene, hydrogen, methane, nitrogen, water, nitrous oxide and acetonitrile were found as primary products, with hydrogen cyanide, carbon monoxide, acetaldehyde, n-butane, 1-butene, cis- and trans-2-butene and 1,3-butadiene as secondary products. For all the primary products the orders with respect to C₂H₆and NO were determined, as were the activation energies at two different percentages of NO (15.7 and 45.5%). Nitric oxide was found to be rapidly consumed with a finite initial rate, and the rate of production of H₂O was close to that of C₂H₄ at higher nitric oxide pressures. A mechanism is proposed which gives good agreement with all of the observed results. Its main features are: (1) Initiation takes place mainly by the unimolecular dissociation of ethane; there is no evidence for or against the process NO + C₂H₆ → HNO + C₂H₅; (2) NO scavenges ethyl radicals to form acetaldoxime which decomposes, and in this way the breakdown of C₂H₅ is hastened; (3) termination takes place mainly by the unimolecular decomposition of acetaldoxime to give inactive products. Some of the relevant rate parameters are evaluated. Reactions are proposed to account for the formation of the secondary products observed.     

Quasi‐Spectral Method for the Solution of the Master Equation for Unimolecular Reaction Systems

Rate constants of elementary reactions involving unimolecular steps can be calculated from molecular data in a most general way by solving appropriate master equations. The conventional numerical solution requires rather a fine discretization applied over a sufficiently large energy range to achieve a reasonable accuracy. This leads to linear but very high‐dimensional systems of differential equations. We propose a quasi‐spectral method that uses Gaussian radial basis functions to establish a low‐dimensional linear model to speed up the numerical integration. The combination with an iterative adaptation provides a further improvement of computational efficiency. The suggested approach is illustrated and exemplified by means of the unimolecular decomposition of 2,3‐dihydro‐2,5‐dimethylfuran‐3‐yl, an intermediate radical occurring in the pyrolysis and oxidation of 2,5‐dimethylfuran. A comparison of the conventional and the proposed method is presented to validate the novel approach and to demonstrate its performance.     

Rate constant and RRKM product study for the reaction between CH3 and C2H3 at T = 298 K

The total rate constant k₁ has been determined at P = 1 Torr nominal pressure (He) and at T = 298 K for the vinyl‐methyl cross‐radical reaction: (1) CH₃ + C₂H₃ → Products. The measurements were performed in a discharge flow system coupled with collision‐free sampling to a mass spectrometer operated at low electron energies. Vinyl and methyl radicals were generated by the reactions of F with C₂H₄ and CH₄, respectively. The kinetic studies were performed by monitoring the decay of C₂H₃ with methyl in excess, 6 < [CH₃]₀/ [C₂H₃]₀ < 21. The overall rate coefficient was determined to be k₁(298 K) = (1.02 ± 0.53) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹ with the quoted uncertainty representing total errors. Numerical modeling was required to correct for secondary vinyl consumption by reactions such as C₂H₃ + H and C₂H₃ + C₂H₃. The present result for k₁ at T = 298 K is compared to two previous studies at high pressure (100–300 Torr He) and to a very recent study at low pressure (0.9–3.7 Torr He). Comparison is also made with the rate constant for the similar reaction CH₃ + C₂H₅ and with a value for k₁ estimated by the geometric mean rule employing values for k(CH₃ + CH₃) and k(C₂H₃ + C₂H₃). Qualitative product studies at T = 298 K and 200 K indicated formation of C₃H₆, C₂H₂, and C₃H₅ as products of the combination‐stabilization, disproportionation, and combination‐decomposition channels, respectively, of the CH₃ + C₂H₃ reaction. We also observed the secondary C₄H₈ product of the subsequent reaction of C₃H₅ with excess CH₃; this observation provides convincing evidence for the combination‐decomposition channel yielding C₃H₅ + H. RRKM calculations with helium as the deactivator support the present and very recent experimental observations that allylic C‐H bond rupture is an important path in the combination reaction. The pressure and temperature dependencies of the branching fractions are also predicted. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 304–316, 2000     

Synthesis of Branched Polyethylene by Tandem Catalysis

Linear low‐density polyethylene (LLDPE) can be prepared by addition of ethylene to a mixture of two catalysts. In this “tandem catalysis” scheme one catalyst dimerizes or oligomerizes ethylene to α‐olefins while the second site incorporates these α‐olefins into a growing polyethylene chain. A variety of classical catalyst combinations are available for this purpose. Better control over the polymerization process, and therefore product properties, is attained by the use of homogenous “single site” catalysts. The best‐behaved tandem processes take advantage of well‐defined catalysts that require stoichiometric quantities of activators. One such system employs [(C₆H₅)₂PC₆H₄C(OB(C₆F₅)₃)O‐κ²P,O]Ni(η³‐CH₂CMeCH₂) and {[(η⁵‐C₅Me₄)SiMe₂(η¹‐NCMe₃)]TiMe}{MeB(C₆F₅)₃}. The nickel sites are responsible for converting ethylene to 1‐butene or mixtures of 1‐butene with 1‐hexene. These olefins are copolymerized with ethylene at the titanium sites. It is possible to obtain a linear correlation between the branching content in the polymer product and the Ni/Ti ratio. The effect of ligand substitution at nickel has also been investigated. When the benzyl derivative [(C₆H₅)₂PC₆H₄C(O‐B(C₆F₅)₃)O‐κ²P,O]Ni(η³‐CH₂C₆H₅) is used instead of the methallyl counterpart [(C₆H₅)₂PC₆H₄C(OB(C₆F₅)₃)O‐κ²P,O]Ni(η³‐CH₂CMeCH₂), one obtains, at a constant Ni/Ti ratio, considerably more branching in the final polymer structure. These results are rationalized in terms of a more efficient initiation when the more labile benzyl ligand is used.     

Effects of buffer gases on the infrared multiphoton dissociation of C2H4DCl: A chemical clock to explore highly excited molecules

Observations are reported of the effect of the buffer gases He, Ne, and CF₄, in the pressure range of 0–30 torr, on the branching ratio [HCl]/[DCl] of the unimolecular decomposition The ratio R = k_H/k_D has been measured in high-pressure thermal decomposition (670–1100 K) and was shown to give a unique measure of the internal energy of the decomposing molecules and hence, with RRKM theory and pressure fall-off data, a time scale for their decomposition. Applying the thermal data to the photolysis leads to the conclusion that excitation and decomposition are produced by the laser spike (high intensity, 70 ns FWHM) and also at a slower rate by the larger, less intense tail (1.6 μs). Added buffer gases quench the latter, leaving the former which, from measurements of R, is shown to correspond to excitations of 115 ± 15 kcal/mol and lifetimes of ～30 ps. No bond breaking is seen despite the high energies, in accord with theoretical expectations. The results require an enhanced rate of photon absorption by the highly excited molecules, which are about hundredfold greater than that observed for 300 K molecules. Data are also reported for C₂H₂F₂ and the secondary multiphoton photolysis of the ethylenes produced. Effects of beam geometry and wavelength are explored.     

Neue Synthesen und Kristallstrukturen von Bis(fluorphenyl)quecksilber,Hg(Rf)2 (Rf = C6F5, 2, 3, 4, 6‐F4C6H, 2, 3, 5, 6‐F4C6H, 2, 4, 6‐F3C6H2, 2, 6‐F2C6H3)

New Syntheses and Crystal Structures of Bis(fluorophenyl) Mercury, Hg(R_f)₂ (R_f = C₆F₅, 2, 3, 4, 6‐F₄C₆H, 2, 3, 5, 6‐F₄C₆H, 2, 4, 6‐F₃C₆H₂, 2, 6‐F₂C₆H₃) Bis(fluorophenyl) mercury compounds, Hg(R_f)₂ (R_f = C₆F₅, C₆HF₄, C₆H₂F₃, C₆H₃F₂), are prepared in good yields by the reactions of HgF₂ with Me₃SiR_f. The crystal structures of Hg(2, 3, 4, 6‐F₄C₆H)₂ (monoclinic, P2₁/n), Hg(2, 3, 5, 6‐F₄C₆H)₂ (monoclinic, C2/m), Hg(2, 4, 6‐F₃C₆H₂)₂ (monoclinic, P2₁/c) and Hg(2, 6‐F₂C₆H₃)₂ (triclinic, P1) are described.     

Very-low-pressure pyrolysis of nitroso- and pentafluoronitrosobenzene C?NO bond dissociation energies

The high-pressure absolute rate constants for the decomposition of nitrosobenzene and pentafluoronitrosobenzene were determined using the very-low-pressure pyrolysis (VLPP) technique. Bond dissociation energies of DH⁰(C₆H₅? NO) = 51.5 ± 1 kcal/mole and DH⁰ (C₆F₅? NO) = 50.5 ± 1 kcal/mole could be deduced if the radical combination rate constant is set at log k_r(M^?1·sec^?1) = 10.0 ± 0.5 for both systems and the activation energy for combination is taken as 0 kcal/mole at 298°K. δH_f⁰(C₆H₅NO), δH_f⁰(C₆F₅NO), and δH_f⁰(C₆F₅) could be estimated from our kinetic data and group additivity. The values are 48.1 ± 1, –160 ± 2, and – 130.9 ± 2 kcal/mole, respectively. C–X bond dissociation energies of several perfluorinated phenyl compounds, DH⁰(C₆F₅–X), were obtained from the reported values of δH_f⁰(C₆F₅X) and our estimated δH_f⁰(C₆F₅) [X = H, CH₃, NO, Cl, F, CF₃, I, and OH].     

Unimolecular isomerization/decomposition of cyclopentadienyl and related bimolecular reverse process: ab initio MO/statistical theory study

The cyclopentadienyl radical decomposition has been studied in detail by high‐level correlation MO methods combined with multichannel RRKM rate constant calculations. The product channels of the reaction were examined by calculating their pressure‐dependent branching rate constants. The overall reaction rate has been shown to be controlled by the first transition state corresponding to 1,2‐hydrogen atom migration. Also, the reverse bimolecular reactions (C₃H₃ + C₂H₂ → products) have been included in the study. We provide a summary of pressure dependent rate constant expressions for the 1000–3000 K temperature range that may be useful for kinetic modeling of relevant combustion systems. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 415–425, 2000