bluuebunny/crossref_metadata_2025_split huggingface dataset:
Direct and sensitized photolysis of bicyclo[4.2.0]octa‐2,4‐diene in the gas phase
Authors: Greathead John M. , Orchard S. Walter 
Published: January 2005

AbstractThe direct photolysis of bicyclo[4.2.0]octa‐2,4‐diene in the gas phase at 280–300 nm produces mainly 1,3,5‐cyclooctatriene and benzene plus ethylene. The yield of the former product is enhanced by added gases, and it is proposed that it is formed in a vibrationally excited state which can revert to bicyclooctadiene unless the excess energy is removed in collisions. Computer modelling of the direct photolysis yielded quantitative agreement with the experimental results, but only when large, arbitrary adjustments were made to the calculated rate constants for the interconversion of cyclooctratriene and bicyclooctadiene. The Hg(63P1) sensitized reaction of bicyclooctadiene produces mainly benzene plus ethylene, a process which is also enhanced by added gases.
Cross‐reaction and cross‐combination ratios
Authors: Arthur Neville L. , Christie John R. 
Published: January 2005

AbstractA simple collision theory model for reaction between two different radicals shows that the cross‐reaction ratio, ϕ*, is 2 only if the masses and collision diameters of the radicals are identical; for all other combinations of mass and size, ϕ* is greater than 2. The value of ϕ* is shown to depend simply on the ratios of the masses and diameters of the two radicals: which of the two is the heavier or larger is unimportant.Calculated and experimental values of ϕ* are compared for several systems involving small alkyl and fluoroalkyl radicals, and the relationship between ϕ* and ϕ, the cross‐combination ratio, is discussed.
Decomposition of the t‐butoxy radical — I. Studies over the temperature range 402–443 K
Authors: Batt L. , Robinson G. N. 
Published: January 2005

AbstractBy allowing the t‐butoxy radical to decompose in the presence of nitric oxide, it has been possible to determine rate constants for decomposition by the measurements of the relative rates (2) and (3)
equation image
Process (3) is clearly pressure dependent. The value of k3(∞) has been determined in the presence of several inert gases (CF4, SF6, N2, and Ar) and a value of k3 interpolated for atmospheric conditions. The results may be compared with those for other relevant alkoxy radicals at room temperature. Extrapolated values for k3 in the presence of CF4 lead to the result
Artificial‐intelligence‐based interpretation of feature sensitivities of the Belousov‐Zhabotinsky reaction
Authors: Györgyi L. , Deutsch T. , Kőrös E. 
Published: January 2005

AbstractA new approach is presented for analyzing kinetic models of relaxation‐type oscillatory systems on the basis of numerical data. Feature sensitivities of the length of the two kinetic states of the Belousov‐Zhabotinsky (BZ) reaction with respect to the rate constants of the model are explained by means of a logic‐based inference system. The main kinetic roles of the individual reaction steps on the relaxing components are revealed, and a consistent interpretation of the kinetic states is given by this process. Both the high and the low set of rate constants were studied. According to our analysis, the bromous acid‐hypobromous acid reaction is an important Br− producing step of the model, and in the case of the low set, the bromate‐bromous acid reaction is not the rate‐determining step of the bromous acid autocatalysis.
Kinetics of the gas‐phase thermal elimination of N‐alkyl‐pyrazoles
Authors: Perez Jorge Daniel , Phagouape Leonardo Miguel 
Published: January 2005

AbstractThe kinetic study of the gas‐phase thermal elimination reactions of N‐ethyl‐3,5 dimethyl‐pyrazole (I), N‐ethyl‐pyrazole (II), N‐sec‐butyl‐pyrazole (III), and N‐tert‐butyl‐pyrazole (IV) using a flow system is reported. After obtaining activation parameters for I we carried out competitive reactions with II, III and IV using I as internal standard to obtain their Ea. The values of Δ(ΔH) calculated for II, III and IV agree with the little differences in Ea experimentally found.
Kinetic study of gas‐phase reactions with CF2Cl2 and CFCl3. Analysis using the transition state theory (TST) of the chlorine atom transfer reactions by CF3 and CH3 radicals from halomethanes
Authors: Taccone R. A. , Salinovich O. , Staricco E. H. 
Published: January 2005

AbstractThe following gas‐phase reactions:
equation image
were studied by the competitive method with CF3I as the source of radicals. The kinetic parameters obtained in the temperature range 533–613 K and 503–613 K respectively for chlorine atom transfer reactions are given by:

where θ = 2.303 RT (cal mol−1).The Arrhenius A values were calculated for seven chlorine atom transfer reactions (CF2Cl2, CFCl3, CCl4 with CF3 radicals; CF3Cl, CF2Cl2, CFCl3 and CCl4 with CH3 radicals) by using the thermochemical kinetic version of the Transition State Theory (TST).
Exchange reactions in selectively excited Br2(B3Π)
Authors: Lum Richard M. , McAfee Kenneth B. 
Published: January 2005

AbstractLaser‐controlled bimolecular isotopic exchange reactions in bromine leading to alterations in natural isotopic abundance ratios have been directly observed using laser‐modulated molecular beams and mass analysis. Several instances of selective excitation and subsequent rapid isotope exchange are observed within the 7 GHz gain curve of the exciting 514.5 nm line of an argon‐ion laser. These exchange processes are attributed to the direct photochemical participation of excited molecular states in the B3Πou+ system of Br2.
Analysis of flow dynamics in a new, very low pressure reactor. Application to the reaction: Cl + CH4⇌ HCl + CH3
Authors: Dobis Otto , Benson Sidney W. 
Published: January 2005

AbstractA new, improved variant of the very low pressure reactor (VLPR) system with interchangeable discharge orifices was used for studying the compatibility of the chemical and physical processes occurring simultaneously. It is shown that the ratio of calculated and effective escape rate constants is a complex function of the reactor cell geometry for reactions of non‐spherical symmetry.The test reaction of atomic chlorine with methane proved to be a pure chemical process free of side reactions and was used to calibrate the system. The measured rate constant is k1 = (0.993 ± 0.013) × 10‐13 cm3/molec‐s at 25°C. A new procedure is outlined for measuring the equilibrium constant by changing the concentrations of all three components resulting in a remarkable accuracy of K1 = 1.406 ± 0.034 for the test reaction at 25°C.
Kinetics of the gas phase reaction of hydroxyl radicals with ethane, benzene, and a series of halogenated benzenes over the temperature range 234–438 K
Authors: Wallington Timothy J. , Neuman Douglas M. , Kurylo Michael J. 
Published: January 2005

AbstractAbsolute rate constants for the gas phase reactions of OH radicals with ethane (k1), benzene (k2), fluorobenzene (k3), chlorobenzene (k4), bromobenzene (k5), iodobenzene (k6), and hexafluorobenzene (k7) have been measured over the temperature range 234–438 K using the flash photolysis resonance fluorescence technique. The rate constants measured at room temperature (296 K), at total pressures of argon diluent between 25 and 50 Torr, were (in units of 10−13 cm3 molecule−1 s−1): k1 = (2.30 ± 0.26), k2 = (12.9 ± 1.4), k3 = (6.31 ± 0.81), k4 = (7.41 ± 0.94), k5 = (9.15 ± 0.97), k6 = (13.2 ± 1.6), and k7 = (1.61 ± 0.24), respectively. The indicated errors are our estimate of 95% confidence limits and include two standard deviations from the least‐squares analysis together with an allowance for any possible systematic errors in the measurements. At elevated temperatures and under pseudo‐first‐order reaction conditions, non‐exponential hydroxyl radical decays were observed for benzene and the monosubstituted halo‐aromatics. For ethane and hexafluorobenzene, exponential decays were observed over the complete temperature range and the data were fit by the Arrhenius expressions: k1 = (8.4 ± 3.1) × 10−12 exp[(−1050 ± 100)/T] and k7 = (1.3 ± 0.3) × 10−12 exp[(−610 ± 80)/T], respectively. The results are compared with previous literature data and the mechanistic implications are discussed.
Kinetic study of the iodine‐catalyzed alcoholysis of Butoxytriethylsilane: n‐butoxy group—s‐butoxy group exchange reaction
Authors: Ito Katsuko , Ibaraki Takeshi 
Published: January 2005

AbstractIn order to appreciate the excellent catalytic effect of iodine on the alcoholyses of alkoxysilanes more precisely, the rates of the reaction, Et3SiOBun + BusOH ⇌ Et3SiOBus + BunOH, were determined at various iodine concentrations.Both forward and reverse reactions are first order with respect to butoxysilane and to butanol, and pseudo first‐order rate constants were measured at 40°, 30°, and 20°C on reaction mixtures containing both butanols in excess by means of gas‐liquid chromatography. The observed rate constants as a function of iodine concentration gave linear relationships, and from these data the catalytic coefficients of iodine were evaluated:

The enthalpies and the entropies of activation were estimated to be 53.2 kJ mol−1, −103 J K−1 mol−1 (forward, 30°C) and 51.8 kJ mol−1, minus;100 J K−1 mol−1 (reverse, 30°C).
Systematic characterization of transition states for radical decompositions
Authors: Grela M. A. , Colussi A. J. 
Published: January 2005

AbstractA one‐parameter analytical potential energy function for β‐bonds in free radicals is described, which accounts quantitatively for their observed stretching frequencies and the position and size of the activation barriers for their fission. It is shown that such a function can be used to characterize a priori the corresponding transition states by assuming that the structural and spectroscopic changes taking place along the minimum energy path track the development of pi bonding rather than following a simple exponential dependence on the reaction coordinate. This procedure, tested by comparing predicted A‐factors and isotope effects with experimental data for alkyl radicals and ab‐initio calculations on C2H5, fully encodes the basic features of radical decomposition reactions and provides a simple, realistic, and self‐consistent technique for the estimation of their kinetic parameters.
Kinetics and mechanisms of substitution at paramagnetic metal centers in organometallic complexes
Authors: Trogler William C. 
Published: January 2005

AbstractThe mechanism of ligand substitution in 17‐ and 19‐electron organometallic radicals is discussed. These species substitute ligands by an associative process some 106 to 1010 faster than analogous 18‐electron complexes. When 17‐electron species can be generated by bond homolysis or electron transfer reactions of 18‐electron complexes, they can act as intermediates in radical chain reactions of 18‐electron complexes. A 17–19 electron rule is proposed to explain transformations of organometallic radicals just as the 16–18 electron rule finds use for closed shell organometallic complexes. The origin of this rule is the favorable two‐center three‐electron bond that can form when an odd electron in a sterically accessible metal d‐orbital interacts with an electron pair on an entering nucleophile. Besides simple substitution, these radicals can disproportionate, dimerize, and undergo insertion or atom abstraction reactions.
Kinetics of the reactions of atomic chlorine with methanol and the hydroxymethyl radical with molecular oxygen at 298 K
Authors: Payne W. A. , Brunning J. , Mitchell M. B. , Stief L. J. 
Published: January 2005

AbstractThe rate constants for the reactions Cl + CH3OD → CH2OD + HCl (1) and CH2OH + O2 → HO2 + H2CO (2) have been determined in a discharge flow system near 1 torr pressure with detection of radical and molecular species using collision‐free sampling mass spectrometry. The rate constant k1, determined from the decay of CH3OD in the presence of excess Cl, is (5.1 ± 1.0) × 10−11 cm3 s−1. This is in reasonable agreement with the only previous measurement of k1. The CH2OH radical was produced by reaction (1) and its reaction with O2 was studied by monitoring the decay of the CH2OH radical in the presence of excess O2. The result is k2 = (8.6 ± 2.0) × 10−12 cm3 s−1. Previous estimates of k2 have differed by nearly an order of magnitude, and our value for k2 supports the more recent high values.
Kinetic analysis of a single‐path, and of a dual‐path, sequence of four first‐order reactions. The reactions of dibenzoylmesitylene and acetylbenzoylmesitylene in sulfuric acid
Authors: Farooqi Jameel A. , Gore Peter H. , Waters David N. , Moxon Gerald F. 
Published: January 2005

AbstractDibenzoylmesitylene undergoes protiodeacylation in 89.8% (w/w) sulfuric acid at ca. 90°C, with subsequent sulfonation, to give mesitylenedisulfonic acid. The reaction involves a single‐path sequence of four first‐order reactions. The corresponding reaction of acetylbenzoylmesitylene can proceed by two possible routes: it is shown that about 94% of the overall reaction at 75° involves initial protiodeacetylation and about 6% initial protiodebenzoylation. The kinetic analyses provide estimates of concentration ratios as functions of time, and of the buildup and decay of intermediates in the reactions.
Atmospheric reactions of chloroethenes with the OH radical
Authors: Tuazon Ernesto C. , Atkinson Roger , Aschmann Sara M. , Goodman Mark A. , Winer Arthur M. 
Published: January 2005

AbstractThe kinetics and products of the homogeneous gas‐phase reactions of the OH radical with the chloroethenes were investigated at 298 ± 2 K and atmospheric pressure. Using a relative rate technique and ethane as a scavenger for the chlorine atoms produced in these OH radical reactions, rate constants (in units of 10−12 cm3 molecule−1s−1) of 8.11 ± 0.24, 2.38 ± 0.14, and 1.80 ± 0.03 were obtained for 1,1‐dichloroethene, cis‐1, 2‐dichloroethene and trans‐1,2‐dichloroethene, respectively. Under these conditions, the major products observed by long pathlength FT‐IR absorption spectroscopy were HCHO and HC(O)Cl from vinyl chloride; HC(O)Cl from cis‐ and trans‐1,2‐dichloroethene; HCHO and COCl2 from 1,1‐dichloroethene; HC(O)Cl and COCl2 from trichloroethene; and COCl2 from tetrachloroethene. In the absence of a Cl atom scavenger, significant yields of the chloroacetyl chlorides, CHxCl3−xC(O)Cl, were observed from 1,1‐dichloro‐, trichloro‐ and tetrachloroethene, indicating that these products resulted from reactions involving chlorine atoms. The yields of all of these products are reported and the mechanisms of these gas‐phase reactions discussed. In addition, OH radical reaction rate constants were redetermined, in the presence of a Cl atom scavenger, for cis‐ and trans‐1,3‐dichloropropene and 3‐chloro‐2‐chloromethyl‐1‐propene, being (in units of 10−12 cm3 molecule−1 s−1) 8.45 ± 0.41, 14.4 ± 0.8, and 33.5 ± 3.0, respectively.
Kinetics of the chlorination of secondary amines by N‐chlorosuccinimide
Authors: Antelo Juan M. , Arce Florencio , Franco Julia , Lopez Maria C. Garcia , Sanchez Maria , Varela Angel 
Published: January 2005

AbstractThe chlorinations of dimethylamine, diethylamine, methylethanolamine, ethylethanolamine and diethanolamine by N‐chlorosuccinimide have been found to be equilibrium reactions of order one with respect to both N‐chlorosuccinimide and amine in the forward direction and of order one with respect to succinimide and the resulting N‐chloramine in the other. These results are explained by postulating a mechanism in which the rate controlling step consists in direct exchange of positive chlorine between the N‐chlorosuccinimide and the amine.
Transesterification of phenyl salicylate II. Kinetics and mechanism of intramolecular general base‐catalyzed cleavage of phenyl salicylate under the presence of 1,2‐ethanediol and 2‐ethoxyethanol
Authors: Khan M. Niyaz 
Published: January 2005

AbstractThe first‐order rate constants, k1, for 1,2‐ethanediolysis (within the content of 1,2‐ethanediol of 5% to 90%, v/v) and 2‐ethoxyethanolysis (within the 2‐ethoxyethanol content of 5% to 60%, v/v) of phenyl salicylate, PSH, in alkaline aqueous mixed solvents, fit to a relationship: k1 = k[ROH]T/(1 + K[ROH]T) where k and K represent the secondorder rate constant for the reaction of alkanol, ROH, with ionized phenyl salicylate, PS−, and association constant for the dimerization of ROH, respectively, and [ROH]T is the total concentration of ROH. Similar relationship between k1 and [ROH]T has been found for 1,2‐ethanediolysis of PS− studied in mixed solvents containing 1,2‐ethanediol and MeCN. In the alkaline aqueous mixed solvents containing 2‐ethoxyethanol, the k1‐[ROH]T profile reveals the change in the solvent structure of the reaction medium at >60% (v/v) of ROH content. It is proposed that alkanols exist in polymeric form, (ROH)n, and the alkanolysis of PS− involves the pre‐equilibrium formation of monomeric ROH from (ROH)n, followed by an intramolecular general base‐catalyzed nucleophilic attack at carbonyl carbon of ester. A slight negative KCl salt‐ and slight positive n‐Bu4NI salt‐effect are obtained for 1,2‐ethanediolysis while a significant positive n‐Bu4NI salt‐effect is obtained for 2‐ethoxyethanolysis of PS−.
Kinetics of the bromine catalyzed elimination of HCl from 1,1,1‐trichloroethane
Authors: Rodgers A. S. , Jerus Paul 
Published: January 2005

AbstractThe gas phase kinetics of the bromine catalyzed elimination of HCl from 1,1,1‐trichloroethane has been studied over a five fold variation of (CH3CCl3)/(Br2) and from 565 to 634 K. The most important reactions in the mechanism are found to be:

equation image

The preferred analysis of the kinetic data results in log(k1/M−1 s−1) = 11.3 ± 0.3 − (19.9 ± 1.0) × 103/4.575 T. From these results one calculates the C—H bond dissociation energy in CH3CCl3 to be 103.8 ± 2 kcal mol−1, and the heat of formation of 2,2,2‐trichloroethyl to be 17.7 ± 2 kcal mol−1.
Kinetic H/D isotope effects for gas phase hydroxylation of benzene and chlorobenzene between 520–1080 K. Hydroxyl radical versus O(3P) atom attack
Authors: Mulder Peter , Louw Robert 
Published: January 2005

AbstractGas phase slow combustion of (chloro)benzene in O2/N2 mixtures, and induced by addends such as tert butylhydroperoxide, cyclohexane, or methanol, leads to (chloro)‐phenol as the only important aromatic product. Using C6H6/C6D6 mixtures, formation of phenol/perdeuterophenol was studied between 520–1080 K. The temperature dependence of this product ratio was found to obey the Arrhenius expression for the intermolecular isotope effect log kH/kD = −0.14 ± 0.03 + (1240 ± 80)/2.303RT (R in cal/mol K). Essentially the same result was obtained for the intramolecular isotope effect, measuring the change in isomer distribution for the chlorophenols formed from p‐deuterio‐chlorobenzene versus those for chlorobenzene.These results are in accordance with H(D)‐abstraction by ·OH, via a linear transition state, as the first and (relative) rate determining step. Whereas above 1000 K, at reduced pressure, the intramolecular isotope effect continues to prevail, C6H6/C6D6 do not show differences in rate of formation of C6H5OH/C6D5OH. Under these conditions, the only effective reaction of arene to phenol appears to be set in by addition of O(3P).
H2S‐promoted thermal isomerization of cis‐2‐pentene to 1‐pentene and trans‐2‐pentene around 800 K
Authors: Perrin D. , Richard C. , Martin R. 
Published: January 2005

AbstractH2S accelerates the thermal isomerization of cis‐2‐pentene (P2c) to 1‐pentene (P1) and trans‐2‐pentene (P2t) to around 800 K. This effect is interpreted on the basis of a free radical mechanism in which 2‐pentenyl and thiyl radicals are the main chain carriers. P1 formation is essentially explained by the competing processes:

equation image

equation image

P2t formation is due to addition‐elimination processes:

equation image

the importance of which has been evaluated against process (−4μ):

equation image

The following ratios of rate constants have been measured and are discussed:

(RT in cal mol−1).
The kinetics of photosensitized thymine dimerization
Authors: Kilfoil Valda , Salter Leo 
Published: January 2005

AbstractSince thymine dimerization is the main photochemical lesion occuring in uv irradiated DNA, an understanding of the mechanism of dimerization is biologically significant. Both photosensitized and direct dimerization are important in DNA, but because photosensitized thymine dimerization has been less thoroughly investigated, this has been the major topic of study in this laboratory. By comparing experimental results with those obtained by computer simulation, attempts have been made to deduce mechanisms for photosensitization by acetone, acetophenone, and benzophenone.Photolysis of photosensitized solutions was performed using a xenon lamp and quantitative detection of dimer was achieved using h.p.l.c. techniques. A program designed to solve differential rate equations was used for the computer simulation of reaction mechanisms.Based on the results obtained it has been confirmed that acetone photosensitization over the entire range of thymine concentration considered (10−4 mol dm−3 to 10−2 mol dm−3) proceeds via diffusion controlled triplet transfer from the photosensitizer to thymine, followed by bimolecular collision of ground and excited state thymine monomers. For acetophenone and benzophenone photosensitization this method applied at low thymine concentrations, but at higher concentrations (<10−3 mol dm−3) predicted far lower yields than those observed experimentally. The effect of thymine base stacking was then considered, but it was found that this did not significantly increase the dimer yield. A mechanism involving association of thymine and photosensitizer molecules was therefore proposed. This mechanism was found to give reasonably good agreement between experimental and computed data. On the basis of present data the authors regard this as the most likely mechanism for thymine dimerization and work is in progress to confirm this proposal.
Gas phase oxidation of tetrahydrofuran
Authors: Molera M. J. , Couto A. , Garcia‐Dominguez J. A. 
Published: January 2005

AbstractThe slow gas‐phase oxidation of tetrahydrofuran was studied under static conditions at 220°C. The relative amounts of each product, if extrapolated to zero reaction time, show which are the primary reaction products, and the reaction stoichiometry was thus established. Rate constants for hydroperoxides production and consumption were calculated; these hydroperoxides are responsible for chain branching. Carbon monoxide and carbon dioxide have been shown to be formed in the early stages of the reaction and not simply as end products of oxidative degradation processes. It has been found that at reaction times close to zero one tetrahydrofuran molecule may be attacked in one or several carbon atoms. 65.9% of tetrahydrofuran consumed in the first stages of the reaction forms succinic acid through a mechanism in which one molecule of fuel is attacked by two molecules of oxygen. More than 20% of the tetrahydrofuran molecules are attacked at least by three molecules of oxygen.