Reactions of chromium atoms with chloromethanes

The rate constants of the gas-phase reactions of the chromium atom with CC1⁴, CHC1₃, and CH₂Cl₂ were measured behind shock waves at 800–1400 K. The results are presented in the Arrhenius form (the activation energy is given in kJ/mol):k _{CCl 4} = 10^14.32±0.36exp[-(2.0±7.5)/RT],k _{CHCl 3} = 10^14.72±0.21exp[-(18.5.±4.0)/RT, andk _{CH 2 Cl 2}> = 10^14.33±0.16exp[-(24.1±3.1)/RT]cm³mol^-1s^-1.     

Steric influence in the direction of elimination of gas-phase pyrolyses of several highly branched secondary acetates

The rate coefficients for the gas-phase pyrolyses of a series of structurally related secondary acetates have been measured in a static system over the temperature range of 289.1–359.5°C and the pressure range 50.0–203.0 torr. The temperature dependence of the rate coefficients is given by the following Arrhenius equations: for 3-hexyl acetate, log k₁ (s^?) = (12.12 ± 0.33) ? (176.1 ± 3.9)kJ/mol/2.203RT; for 5-methyl-3-hexyl acetate, log k₁ (s^?) = (13.17 ± 0.20) ? (186.2 ± 2.3)kJ/mol/2.303RT; and for 5,5-dimethyl-3-hexyl acetate, log k₁ (s^?) = (12.70 ± 0.19) ? (177.4 ± 2.2)kJ/mol/2.303RT. The direction of elimination of these esters has shown from the invariability of olefin distributions at different temperatures and percentages of decomposition that steric hindrance is a determining factor in the eclipsed cis conformation. Moreover, a more detailed analysis indicates that the greater the alkyl–alkyl interaction, the less favored the elimination tends to be. Otherwise, an increase of alkyl–hydrogen interaction caused steric acceleration to be the determining factor.     

Linear correlation of polar substituents in the gas-phase pyrolyses of ethyl α-substituted acetates

The pyrolysis kinetics of several ethyl esters with polar substituents at the acyl carbon have been studied in the temperature range of 319.8–400.0°C and pressure range of 50.5–178.0 torr. These eliminations are homogeneous, unimolecular, and follow a first-order rate law. The rate coefficients are given by the Arrhenius equations: for ethyl glycolate, log k₁ (s^?1) = (12.75 ± 0.30) – (201.4 ± 3.8) kJ/mol/2.303RT; for ethyl cyanoacetate, log k₁ (s^?1) = (12.19 ± 0.18) – (191.8 ± 2.1) kJ/mol/2.303RT; for ethyl dichloroacetate, log k₁ (s^?1) = (12.62 ± 0.36) – (193.9 ± 4.3) kJ/mol/2.303RT; for ethyl trichloroacetate, log k₁ (s^?1) = (12.27 ± 0.09) – (185.1 ± 1.0) kJ/mol/2.303RT. The results of the present work together with those reported recently in the literature give an approximate linear correlation when plotting log k/k₀ vs. σ* values (ρ* = 0.315 ± 0.004, r = 0.976, and intercept = 0.032 ± 0.006 at 400°C). This linear relationship indicates that the polar substituents affect the rate of elimination by electronic factors. The greater the electronegative nature of the polar substituent, the faster is the pyrolysis rate. The alkyl substituents yield, within experimental error, similar values in rates which makes difficult an adequate assessment of their real influence.     

Pulsed laser polymerization study of the propagation kinetics of acrylamide in water

Pulsed laser polymerization was used in conjunction with aqueous‐phase size exclusion chromatography with multi‐angle laser light scattering detection to determine the propagation rate coefficient (k_p) for the water‐soluble monomer acrylamide. The influence of the monomer concentration was investigated from 0.3 to 2.8 M, and k_p decreased with increasing monomer concentration. These data and data for acrylic acid in water were consistent with this decrease being caused by the depletion of the monomer concentration by dimer formation in water. Two photoinitiators, uranyl nitrate and 2,2′‐azobis(2‐amidinopropane) (V‐50), were used; k_p was dependent on their concentrations. The concentration dependence of k_p was ascribed to a combination of solvent effects arising from association (thermodynamic effects) and changes in the free energy of activation (effects of the solvent on the structure of the reactant and transition state). Arrhenius parameters for k_p (M^?1 s^?1) = 10^7.2 exp(?13.4 kJ mol^?1/RT) and k_p (M^?1 s^?1) = 10^7.1 exp(?12.9 kJ mol^?1/RT) were obtained for 0.002 M uranyl nitrate and V‐50, respectively, with a monomer concentration of 0.32 M. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1357–1368, 2005     

Thermal unimolecular isomerization of 1,4-dimethylbicyclo[2.2.0]hexane, 1,4-dimethylbicyclo[2.1.1]hexane,and 1,4-dimethylbicyclo[2.1.0]pentane

The thermal isomerization of the title compounds was studied in the vapor phase. Over the temperature range from 445.1 to 477.5°K, 1,4-dimethylbicyclo[2.2.0]hexane underwent a homogeneous unimolecular reaction to 2,5-dimethyl-1,5-hexadiene, the rate constants being represented by the equation: k = 1.86 × 10¹¹ exp (?31000 ± 1800/RT) sec^?1. Over the temperature range from 630.0 to 662.2°K, 1,4-dimethylbicyclo[2.1.1]-hexane also underwent a unimolecular isomerization to the same product, the rate constants being given by the equation: k = 8.91 × 10¹⁴ exp (?56000 ± 900/RT) sec^?1. The pyrolysis of 1,4-dimethylbicyclo[2.1.0]pentane gave 1,3-dimethylcyclopentene-1 and 2,4-dimethyl-1,4-pentadiene in the ratio of 9:1. The former reaction was influenced by surface effects but the latter was not. The rate constants for the formation of 2,4-dimethyl-1,4-pentadiene fitted the equation: k = 1.66 × 10¹⁷ exp (?57400 ± 3100/RT) sec^?1. The effect of the two methyl groups at the bridgehead positions in these molecules in influencing the rate of decomposition is discussed in terms of the non-bonded repulsive forces between the substituents.     

Kinetic and Mechanisms of the Homogeneous,Unimolecular Elimination of Phenyl Chloroformate and p‐Tolyl Chloroformate in the Gas Phase

The gas‐phase elimination of phenyl chloroformate gives chlorobenzene, 2‐chlorophenol, CO₂, and CO, whereasp‐tolyl chloroformate produces p‐chlorotoluene and 2‐chloro‐4‐methylphenol CO₂ and CO. The kinetic determination of phenyl chloroformate (440–480^oC, 60–110 Torr) and p‐tolyl chloroformate (430–480°C, 60–137 Torr) carried out in a deactivated static vessel, with the free radical inhibitor toluene always present, is homogeneous, unimolecular and follows a first‐order rate law. The rate coefficient is expressed by the following Arrhenius equations: Phenyl chloroformate: Formation of chlorobenzene, log k_I = (14.85 ± 0.38) – (260.4 ± 5.4) kJ mol^?1 (2.303RT)^?1; r = 0.9993 Formation of 2‐chlorophenol, log k_II = (12.76 ± 0.40) – (237.4 ± 5.6) kJ mol^?1(2.303RT)^?1; r = 0.9993 p‐Tolyl chloroformate: Formation of p‐chlorotoluene: log k_I = (14.35 ± 0.28) – (252.0 ± 1.5) kJ mol^–1 (2.303RT)^?1; r = 0.9993 Formation of 2‐chloro‐4‐methylphenol, log k_II = (12.81 ± 0.16) – (222.2 ± 0.9) kJ mol^?1(2.303RT)^–1; r = 0.9995 The estimation of the k_I values, which is the decarboxylation process in both substrates, suggests a mechanism involving an intramolecular nucleophilic displacement of the chlorine atom through a semipolar, concerted four‐membered cyclic transition state structure; whereas the k_II values, the decarbonylation in both substrates, imply an unusual migration of the chlorine atom to the aromatic ring through a semipolar, concerted five‐membered cyclic transition state type of mechanism. The bond polarization of the C–Cl, in the sense C^{δ+ …} Cl^δ?, appears to be the rate‐determining step of these elimination reactions.     

Neighboring olefinic double-bond participation in gas phase pyrolysis of some alkenyl chlorides

4-Chloro-1-butene, 5-chloro-1-pentene, and 6-chloro-1-hexene have been shown to decompose, in a static system, mainly to hydrogen chloride and the corresponding alkadienes. In packed and unpacked clean Pyrex vessels the reactions were significantly heterogeneous. However, in a vessel seasoned with allyl bromide these reactions were homogeneous, unimolecular, and follow a first-order law. The working temperature range was 389.6–480.0°C and with a pressure range of 53–221 Torr. The rate constants for the homogeneous reactions were expressed by the following Arrhenius equations: 4-chloro-1-butene: logk(sec^?1) = (13.79 ± 0.17) – (223.8 ± 2.1)kJ/mole/2.303RT; 5-chloro-1-pentene: logk(sec^?1) = (14.25 ± 1.20) – (238.4 ± 12.7)kJ/mole/2.303RT; and 6-chloro-1-hexene: logk(sec^?1) = (12.38 ± 0.22) – (209.6 ± 2.9)kJ/mole/2.303RT. The olefinic double bond has been found to participate in the rate of dehydrohalogenation of 4-chloro-1-butene. The insulation of the CH₂?CH in chlorobutene by one or two methylene chains to the reaction center does not indicate neighboring group participation. The three-membered conformation is the most favored structure for anchimeric assistance of the double bond in gas phase pyrolysis of alkenyl chlorides. The heterolytic nature of these eliminations is also supported by the present work.     

Gel permeation chromatographic determination of activation rate constants in nitroxide-controlled free radical polymerization, 1. Direct analysis by peak resolution

The dissociation rate constant k_d related to the homolytic cleavage of the C ON bond formed between a polystyrene (PS) and 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) is determined by adopting the gel permeation chromatography peak-resolution method to the styrene polymerization with a PS-TEMPO adduct as a probe and the radical initiator tert-butyl hydroperoxide. The result was given by the Arrhenius equation, k_d = A exp(−E/(RT)) with A = 3.0 × 10¹³ s⁻¹ and E = 124 kJ · mol⁻¹.     

Shock tube studies of the N2O/Ar and N2O/H2/Ar systems

N₂O decay has been monitored via infrared emission for a series of mixtures containing N₂O/Ar and N₂O/H₂/Ar. These mixtures were studied behind reflected shock waves in the temperature interval of 1950–3075°K with total concentrations ranging from 1.2 to 2.5 × 10¹⁸ molec/cm³. In all cases the N₂O decayed exponentially, and a rate constant k_obs was obtained. Runs without added H₂ could be described by the following Arrhenius parameters: log A = ?9.72 ± 0.08 (in units of cm³/molec · sec) and E_A = 203.5 ± 3.6 kJ/mole. Addition of 0.01% and 0.1% H₂ was observed to increase the decay rate; the largest increase occurred between 2250 and 2500°K with 0.1% H₂, where k_obs doubled. Mixtures with no added H₂ were analyzed by numerical integration of the following reactions: Quantitative agreement between calculations and observations were obtained with both high and low choices for k₂ and k₃. The additional reactions were included in the analysis of the mixtures containing H₂. Here agreement was obtained only when low values were assigned to k₂ and k₃. The combinations of k₁ ← k₃ which agreed with all the data were k₁ = 3.25 × 10^?10 exp (?215 kJ/RT) and k₂ = k₃ = 1.91 × 10^?11 exp (-105 kJ/RT).     

The pyrolysis kinetics of ethyl esters in the gas phase. The alkyl substituent effect at the acyl carbon

The gas-phase elimination of ethyl 3-methylbutanoate and ethyl 3,3-dimethylbutanoate has been studied, in a static system, over the temperature range of 360–420°C and in the pressure range of 71–286 torr. The reactions are homogeneous, unimolecular, and follow a first-order rate law. The temperature dependence of the rate coefficients is given by the following Arrhenius equations: for ethyl 3-methylbutanoate, log k₁ (s^?1) = (12.70 ± 0.36) – (202.5 ± 4.4) kJ/mol/2.303RT, and for ethyl 3,3-dimethylbutanoate, log k₁ (s^?1) = (13.04 ± 0.08) – (207.1 ± 1.0) kJ/mol/2.303RT. Alkyl substituents at the acyl carbon of ethyl esters yield very close values in rates. Consequently it is rather difficult to offer some conclusion concerning the effect of these substituents.     

Temperature‐dependent rate coefficient measurements for the reaction of bromine atoms with a series of aldehydes

Relative rate coefficient data have been obtained for the reactions Br + RCHO → RCO + HBr for a series of aldehydes: HCHO, reaction (1); CH₃CHO, reaction (2); CH₃CH₂CHO, reaction (3); CH₃CH₂CH₂CHO, reaction (4). Measurements were made over the temperature range 240–300 K in an environmental chamber/FTIR spectrometer system, using standard relative rate techniques. All measured rate coefficient ratios were found to be independent of temperature over the range studied (k₂/k₁ = 3.60 ± 0.29, k₃/k₁ = 6.65 ± 0.53, k₄/k₁ = 8.62 ± 0.69, and k₃/k₂ = 1.80 ± 0.14), implying that the activation barriers for all four reactions are essentially identical with the A‐factors increasing with the size of the aldehyde. Relative rate coefficients for k₁ and k₂ agree well with currently recommended data at room temperature, but inconsistencies on the order of 20% arise at lower temperatures. The entire set of relative rate coefficient measurements is put on an absolute scale using a combination of currently recommended values for k₁ and k₂. The following expressions (all in units of cm³ molecule⁻¹ s⁻¹) are obtained: k₁ = (0.79 ± 0.10) × 10⁻¹¹ exp(−580 ± 200/T), k₂ = (2.7 ± 0.4) × 10⁻¹¹ exp(−567 ± 200/T), k₃ = (5.75 ± 0.75) × 10⁻¹¹ exp(−610 ± 200/T), k₄ = (5.75 ± 0.75) × 10⁻¹¹ exp(−540 ± 200/T), where uncertainties quoted for the A‐factor reflect the uncertainty in the room temperature value. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 460–465, 2000     

Temperature dependence of the reaction rate constants for O(3P) atoms with C2H4, C3H6 and NO(M = N2O), determined by a modulation technique

Rate constants for the reaction of O(³P) atoms with C₃H₄, C₃H₆ and NO(M = N₂O) have been measured over the temperature range 300–392°K using a modulation-phase shift technique. The Arrhenius expressions obtained are:C₂H₄, k₂ = 3.37 × 10⁹ exp[?(1270 ± 200)/RT]liter mole^?1 sec^?1,C₃H₆, k₂ = 2.08 × 10⁹ exp[?(0 ± 300)/RT]liter mole^?1 sec^?1,NO(M = N₂O), k₁ = 9.6 × 10⁹ exp[(900 ± 200/RT]liter² mole^?2 sec^?1.These temperature dependencies of k₂ are in good agreement with recent flash photolysis-resonance flourescence measurements, although lower than previous literature values.     

A computational study of the reaction kinetics of methyl radicals with trifluorohalomethanes

Ab initio calculations have been used to characterize the transition states for halogen abstraction by CH₃ in reactions with CF₄, CF₃Cl, CF₃Br, and CF₃I (1–4). Geometries and frequencies were obtained at the HF/6-31G(d) and MP2=full/6-31G(d) levels of theory. Energy barriers were computed via the Gaussian-2 methodology, and the results were employed in transition state theory analyses to obtain the rate constants over 298–2500 K. There is good accord with literature measurements in the approximate temperature range 360–500 K for reactions (2–4), and the computed activation energies are accurate to within ±6 kJ mol⁻¹. Recommended rate constant expressions for use in combustion modeling are k;₁=1.6×10⁻¹⁹ (T/K)^2.41 exp(−13150 K/T), k₂=8.4×10⁻²⁰(T/K)^2.34 exp(−5000 K/T), k₃=4.6×10⁻¹⁹ (T/K)^2.05 exp(−3990 K/T), and k₄=8.3×10⁻¹⁹ (T/K)^2.18 exp(−1870 K/T) cm³ molecule⁻¹ s⁻¹. The results are discussed in the context of flame suppression chemistry. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 179–184, 1998.     

Kinetic study of isothermal oil shale pyrolysis: 1. Mathematical model of the evolution of organic pyroproducts

An isothermal fluidized bed reactor was used for a kinetic study of oil shale pyrolysis. The rate of volatile hydrocarbon evolution was monitored by flame ionization detector. An innovative approach to the data obtained, which we adopted in the present study, led us to a simple kinetic model. The rate of volatile hydrocarbon evolution is described as a linear combination of three parallel independent first-order reactions characterized by three rate constants, k₁ = 2.6·10⁶ exp(−23.6 kcal/RT) s⁻¹, k₂ = 2.3·10⁶ exp(−26.0 kcal/RT) s⁻¹ and k₃ = 9.3·10⁵ exp(−28.1 kcal/RT) s⁻¹. The kinetic effect due to the particle size of the sample is probably due to heat transfer effects.     

The kinetics and mechanisms of methyl 2-bromopropionate and 2-bromopropionic acid pyrolyses under maximum inhibition

The kinetics of the gas phase pyrolyses of methyl 2-bromopropionate and 2-bromopropionic acid were studied in a seasoned, static reaction vessel and under maximum inhibition of the free radical suppressor toluene. The working temperature and pressure range was 310–430°C and 26.5–201.5 torr, respectively. The reactions proved to be homogeneous, unimolecular, and obeys a first-order rate law. The rate coefficients are expressible by the following equations: for methyl 2-bromopropionate, log k₁(s^?1) = (13.10 ± 0.34) ? (211.4 ± 4.4)kJ mol^?1(2.303RT)^?1; for 2-bromopropionic acid, log k₁(s^?1) = (12.41 ± 0.29) ? (180.3 ± 3.4)kJ mol^?1(2.303RT)^?1. The bromoacid yields acetaldehyde, CO and HBr. Because of this result, the mechanism is believed to proceed via a polar five-membered cyclic transition state.     

The kinetics and mechanisms of the gas-phase unimolecular eliminations of halogeno esters. Participation of the carbomethoxy group

The kinetics of the gas-phase elimination of several chloroesters were determined in a static system over the temperature range of 410–490°C and the pressure range of 47–236 torr. The reactions in seasoned vessels, and in the presence of a free-radical inhibitor, are homogeneous, unimolecular, and follow a first-order law. The temperature dependence of the rate coefficients is given by the following Arrhenius equations: for methyl 3-chloropropionate, log k₁(s^?1) = (13.22 ± 0.07) - (231.5 ± 1.0) kJ/mol/2.303RT; for methyl 4-chlorobutyrate, log k₁(s^?1) = (13.31 ± 0.25) - (221.5 ± 3.4) kJ/mol/2.303RT; and for methyl 5-chlorovalerate, log k₁(s^?1) = (13.12 ± 0.25) - (221.7 ± 3.2) kJ/mol/2.303RT. Rate enhancements and lactone formation reveal the participation of carbonyl oxygen of the carbomethoxy group. The order COOCH₃-5 > COOCH₃-6 > COOCH₃-4 in assistance is similar to the sequence of group participation in solvolysis reactions. The partial rates for the parallel eliminations to normal dehydrohalogenation products and lactones have been estimated and reported. The present results lead us to consider that an intimate ion-pair mechanism through participation of the carbomethoxy group may well be operating in some of these reactions.     

The elimination kinetics and mechanisms of ethyl piperidine‐3‐carboxylate,ethyl 1‐methylpiperidine‐3‐carboxylate,and ethyl 3‐(piperidin‐1‐yl)propionate in the gas phase

The gas‐phase elimination kinetics of the above‐mentioned compounds were determined in a static reaction system over the temperature range of 369–450.3°C and pressure range of 29–103.5 Torr. The reactions are homogeneous, unimolecular, and obey a first‐order rate law. The rate coefficients are given by the following Arrhenius expressions: ethyl 3‐(piperidin‐1‐yl) propionate, log k₁(s^?1) = (12.79 ± 0.16) ? (199.7 ± 2.0) kJ mol^?1 (2.303 RT)^?1; ethyl 1‐methylpiperidine‐3‐carboxylate, log k₁(s^?1) = (13.07 ± 0.12)–(212.8 ± 1.6) kJ mol^?1 (2.303 RT)^?1; ethyl piperidine‐3‐carboxylate, log k₁(s^?1) = (13.12 ± 0.13) ? (210.4 ± 1.7) kJ mol^?1 (2.303 RT)^?1; and 3‐piperidine carboxylic acid, log k₁(s^?1) = (14.24 ± 0.17) ? (234.4 ± 2.2) kJ mol^?1 (2.303 RT)^?1. The first step of decomposition of these esters is the formation of the corresponding carboxylic acids and ethylene through a concerted six‐membered cyclic transition state type of mechanism. The intermediate β‐amino acids decarboxylate as the α‐amino acids but in terms of a semipolar six‐membered cyclic transition state mechanism. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 106–114, 2006     

The intimate ion pair mechanism in the maximally inhibited elimination kinetics of methyl 4-chlorobutyrate and methyl 5-chlorovalerate in the gas phase

The gas phase elimination of methyl 4-chlorobutyrate and methyl 5-chlorovalerate has been reexamined, in a static system and seasoned vessel, over the temperature range of 419.6–472.1°C and pressure range of 45–108 torr. The reactions, under maximum inhibition with propene, are homogeneous, unimolecular, and obey a first-order rate law. The rate coefficients are given by the following Arrhenius equations: for methyl 4-chlorobutyrate, log (k₁(s^?1) = (13.41 ± 0.60) - (226.8 ± 8.2) kJ/mol/2.303RT; and for methyl 5-chlorovalerate, log k₁(s^?1) = (13.20 ± 0.02) - (227.6 ± 0.3) kJ / mol / 2.303RT. The pyrolysis rates are found to be about a half of the rates reported in a previous work. As already advanced, the carbomethoxy substituent appears to provide anchimeric assistance in the elimination process, where normal dehydrochlorination and lactone formation arise from an intimate ion pair type mechanism. The partial rates towards each of these products have been determined and reported.     

Direct measurements of the reaction H + CH2O → H2 + HCO behind shock waves by means of Vis–UV detection of formaldehyde

The combination of sensitive detection of formaldehyde by 174 nm absorption and use of ethyl iodide as a hydrogen atom source allowed direct measurements of the reaction H + CH₂O → H₂ + HCO behind shock waves. The rate constant was determined for temperatures from 1510 to 1960 K to be k₂ = 6.6 × 10¹⁴ exp(?40.6 kJ mol^?1/RT) cm³ mol^?1 s^?1 (Δ log k₂ = ± 0.22) Considering the low uncertainty in k₂, which accounts both for experimental and mechanism‐induced contributions, this result supports the upper range of previously reported, largely scattered high temperature rate constants. Vis–UV light of 174 nm was generated by a microwave N₂ discharge lamp. At typical reflected shock wave conditions of 1750 K and 1.3 atm, as low as 33 ppm formaldehyde could be detected. High temperature absorption cross sections of CH₂O and other selected species have been determined. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 374–386, 2002     

Pyrolysis of vinylacetylene between 300 and 450°C

Vinylacetylene was pyrolyzed at 300–450°C in a packed and an unpacked static reactor with a pinhole bleed to a quadrupole mass spectrometer. The reactant and C₈H₈ products were monitored continuously during a reaction by mass spectrometry. In some runs, the products were also analyzed by gas chromatography after the run. In these runs CH₄, C₂H₆, C₃H₆, and C₂H₄ were also detected. The reaction for vinylacetylene removal and C₈H₈ formation is homogeneous, second order in reactant, and independent of the presence of a large excess of N₂ or He. However, C₈H₈ formation is about half-suppressed by the addition of the free-radical scavengers NO or O₂. The rate coefficient for total vinylacetylene removal is 1.7 × 10⁶ exp(?79 ± 13 kJ/mol RT) L/mol · s. The major reaction for C₄H₄ removal is polymerization. In addition four C₈H₈ isomers, carbon, and small hydrocarbons are formed. The three major C₈H₈ isomers are styrene, cyclooctatetraene (COT), and 1,5? dihydropentalene (DHP). The C₈H₈ compounds are formed by both molecular and free-radical processes in a second-order process with an overall k ? 3 × 10⁸ exp(?122 kJ/mol RT) L/mol · s (average of packed and unpacked cell results). The molecular process occurs with an overall k = 8.5 × 10⁷ exp (?118 kJ/mol RT) L/mol · s. The COT, DHP, and an unidentified isomer (d), are formed exclusively in molecular processes with respective rate coefficients of 4.4 × 10⁴ exp(?77 kJ/mol RT), 1.7 × 10⁵ exp(?89 kJ/mol RT), and 3.1 × 10⁹ exp(? 148 kJ/mol RT) L/mol · s. The styrene is formed both by a direct free-radical process and by isomerization of COT.