Hydrocarbons absolute rate constants

In the temperature-dependence study of Perry, Atkinson, and Pitts (264) for the reaction of OH radicals with the aromatic hydrocarbons, absolute rate constants were determined over the temperature range 297 to 473 K using a flash photolysis-resonance fluorescence technique. In all cases, as the temperature was Increased from j298 K the following characteristics were observed (264) ... 

Because of the importance of hydroperoxy radicals in autoxidation processes, their reactions with hydrocarbons arc well known. However, reactions with monomers have not been widely studied. Absolute rate constants for addition to common monomers are in the range 0.09-3 M"1 s"1 at 40 °C. These are substantially lower than kL for other oxygen-centered radicals (Table 3.7). 454... 

An interesting approach to studies of the effects of coordination on the reactivity of lithium polydienes in hydrocarbon solvents was developed by Erussalimski and his colleagues 151 154 The polymerization of lithium polyisoprene in hexane is accelerated by the addition of TMEDA152), the rate levels off at a value of R = [TMEDA]/[li-thium polyisoprene] of 8, its final value giving the absolute rate constant of propagation of the polyisoprene coordinated with TMEDA, namely 0.17 M7l s at 20 °C. 

The intramolecular 1,2-H shifts of alkylchlorocarbenes are often very rapid making it difficult to relate structure with reactivity in terms of absolute rate constants. For example the ku values of Me2CHCCl, PhCHMeCCl, and EtCCl exceed 108 s 1 in hydrocarbon solvents at 25°C (Table 4).60 86 87 However, due to the stabilizing effect of the oxa spectator substituent, acetoxycarbenes react at much reduced rates relative to their chlorocarbene analogues,90,91 thus providing kinetically accessible results for a wide array of bystander-substituted alkylacetoxycarbenes.81 92... 

Atkinson, R., and J. N. Pitts, Jr. Temperature dependence of the absolute rate constants for the reaction of 0( P) atoms with a series of aromatic hydrocarbons over the range 299-392 K. J. Phys. Chem. 79 295-297, 1975. 

Electron spin resonance spectra of the resulting phosphoroalkyl radicals were obtained. Absolute rate constants for this process are not known, and similar abstraction by a peroxy radical in nonaqueous media is not necessarily possible. However, in a zinc salt-inhibited hydrocarbon oxidation the additional reactions in Scheme 2 might be envisaged part molecules are shown for convenience. 

A New Method for Determining the Absolute Rate Constants of Autoxidation of Some Hydrocarbons... 

Singlet NH inserts into the CH bonds of hydrocarbons, much like singlet methylene (see Chapter 7 in this volume). Triplet NH abstracts hydrogen atoms from hydrocarbons to form aminyl (NHp radicals and alkyl radicals in the same manner as triplet methylene, in spite of the fact that the reactions of CH2 are exothermic, whereas some reactions of NH are endothermic, depending on the alkane Absolute rate constants for many of these processes have been measured in the gas phase. However, the gas-phase chemistry of methylene is much more developed than that of imidogen. ... 

Adamic K, Howard JA, Ingold KU (1969) Absolute rate constants for hydrocarbon autoxidation. XVI. 

Furimsky E, Howard JA, Selwyn J (1980) Absolute rate constants for hydrocarbon autoxidation. 28. A low temperature kinetic electron spin resonance study of the self- reactions of isopropylperoxy and related secondary alkylperoxy radicals in solution. Can J Chem 58 677-680 Gebicki JM, Allen AO (1969) Relationship between critical micelle concentration and rate of radiolysis of aqueous sodium linolenate. J Phys Chem 73 2443-2445 Gebicki JM, Bielski BHJ (1981) Comparison of the capacities of the perhydroxyl and the superoxide radicals to initiate chain oxidation of linoleic acid. J Am Chem Soc 103 7020-7022 Gilbert BC, Holmes RGG, Laue HAH, Norman ROC (1976) Electron spin resonance studies, part L. Reactions of alkoxyl radicals generated from alkylhydroperoxidesand titanium(lll) ion in aqueous solution. J Chem Soc Perkin Trans 2 1047-1052... 

Table 17. Absolute rate constants for 5-hexenyl radical cyclizations involving fluorinated radical addition to hydrocarbon alkens, at 30 °C in C6D6 [140,162] ...

TABLE 10. Absolute rate constants (in units of 109 M 1 s ) for reaction of 19a with various reagents in hydrocarbon, MeCN and THF solution at 23 - 25 °C... 

Kinetic studies have recently been reported in an effort to assess systematically the effects of substituents at silicon and carbon on silene reactivity, and put the earlier theoretical work on a firm experimental basis111,117. Absolute rate constants for addition of methanol served as the diagnostic indicator of silene reactivity in these studies, since methanol addition is mechanistically the best understood reaction of transient silenes (vide infra) and can be studied under the widest possible range of conditions in photochemical experiments. Both studies were carried out in hydrocarbon solution at 23 °C, so as to provide a standard set of experimental conditions for the analysis and to minimize the effects of solvation on Si=C reactivity. 

Absolute rate constants have been reported for the reaction of aliphatic alcohols with the transient disilenes 103, 104 and 35 in hydrocarbon solvents and are collected in Table 1768, l48. In all cases, linear dependences of fcdecay on alcohol concentration were observed, indicative of a mechanism that is first order in alcohol over the range of concentrations examined. Product studies carried out with 103 (equation 78) indicate that the reaction is highly regioselective, with the alkoxy group affixing itself to the less hindered... 

Using t = 0.3 ps from the products r kes we straightforwardly calculate absolute rate constants of NO3, H202 and HCIO4 with quasi-free electrons, namely 2 1013, 5 1012 and 1012 M-1s-1, respectively. These values are comparable with the corresponding rate constants in those hydrocarbons where excess electrons are in a quasi-free state only [2]. 

Absolute rate constants have been measured for silylone reactions with hydrocarbons ah .98 K and these show that si lyl ene reacts rapidly but unselective.ly with unsaturated hydrocarbons however, si lyl ene is unreactive towards al kanes- Dimethylsilylene has been produced by y-irradiation of benzene solutions of dodecamethylcyclohexasilane. Relative rate constants for the reactions of methylphenylsilylene generated by photolysis of the Si-bridged arene ( .) with KhOH, Kt-3SiH, and... 

The competition with the thermal back-decomposition of the adduct, kdecomp was studied by lowering the O2 concentration in chamber experiments on benzene, toluene, and /7-xylene (with photolysis of H2O2 as NOx-free source of OH) [5]. At low levels of O2, the removal of the aromatics (observed by cryo-focusing/ GC/FID) corresponds to the abstraction channel, and increases to the sum of abstraction and addition in the limit of high O2. In Table 2, ratios decomp obtained from such measurements are compared to those calculated from our absolute rate constants. That an earlier chamber study on toluene and p-xylene [24] shows much less O2 dependence, has been attributed [19] to rather high concentrations of hydrocarbons, H2O2, and thus radicals in their experiments leading to further loss processes of the adduct. 

Howard, J. A. Schwahn, W. J. Ingold, K. U. Absolute Rate Constants for Hydrocarbons autoxidation. VII. The Reactivities of Peroxy Radicals towards Hydrocarbons and Hydroperoxides, In Preprints of the International Oxidation Simposium. San Francisco, California. 1967 1, 3. 

S. G. Lias, R. E. Rebbert, and P. Ausloos, Gas phase pulse radiolysis of hydrocarbon mixtures determination of the recombination rate coefficient and absolute rate constants of ion-molecule reactions of the r-butyl ion through a competitive kinetic method, J. Res. Natl. Bur. Std., in press. 

In the 60 s, Dr. Szwarc s studies of living polymers shifted toward kinetic problems. Much effort was placed on studying the formation and reaction of complexes of living polymers with aromatic hydrocarbons, kinetics of electron transfer processes, spontaneous isomerization of living polymers, chemistry of radical-anions, etc. Absolute rate constants of propagation were reported in a series of papers published by J. Phys. Chem., 69, 608, 612, 624 (1965). The results revealed that ion-pairs and free ions participate in... 

Phenyl radicals have an important role to play in the combustion of fossil fuels and in the formation of polycyclic aromatic hydrocarbons. The absolute rate constant for the reaction of CeHs with 2-methylpropane, 2,3-dimethylbutane and 2,3,4-trimethylpentane has been measured using cavity ring-down spectromehy between 290 and 500 K. The reactions were found to be dominated by the extraction of H atoms from the tertiary C—H bonds. ... 

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