Showing papers on "Hydrogen atom abstraction published in 1982"
TL;DR: 3-Picolinyl esters were obtained from n-, iso-, anteiso, and unsaturated long chain fatty acids and were examined by gas chromatography and mass spectrometry.
Abstract: 3-Picolinyl esters were prepared from n-, iso-, anteiso- and unsaturated long chain fatty acids and were examined by gas chromatography and mass spectrometry The spectra contained ions which were diagnostic of the position of both the methyl branching and the double bond, and could be rationalized by assuming hydrogen abstraction from the chain by the nitrogen of the pyridine ring and cleavage at the resulting radical site The derivatives were easy to prepare and gave more informative spectra than the previously used pyrrolidides
183 citations
TL;DR: In this paper, a complete product analysis was made with cyclohexene, and these data allow the calculation of the fraction of the NO/sub 2/ that reacts by addition to the double bond or by abstraction of an allylic hydrogen.
Abstract: The reactions of nitrogen dioxide in a carrier gas (nitrogen, oxygen, or air) with cyclohexene and a series of mono-, di-, and trienes is reported at NO/sub 2/ concentrations ranging from 70 ppM to 50%. A complete product analysis was made with cyclohexene, and these data allow the calculation of the fraction of the NO/sub 2/ that reacts by addition to the double bond or by abstraction of an allylic hydrogen. At high concentrations of NO/sub 2/, addition is the predominant process, in agreement with the literature. However, below 10,000 ppM (1%), hydrogen abstraction predominates. It is suggested this is because of competition between a reversible addition and an irreversible H-abstraction step, much as is the case for the well-known bromine atom reaction system. In fact, a kinetic analysis shows that the ratios of rate constants for addition and abstraction are similar for both NO/sub 2/ and the bromine atom. A less direct method (analysis of water formed) was used to estimate the addition to abstraction ratio for other alkenes and for esters of unsaturated fatty acids; these data are in agreement with the cyclohexene data. The autoxidation of unsaturated fatty acid esters initiated by NO/sub 2/ also was studied,more » and kinetic chain lengths and autoxidizability ratios are given.« less
147 citations
TL;DR: The possibilities, use, and limitations of the laser flash photolysis technique to studies in the area of biradical reactions are discussed in this paper, and the reactions show characteristic behavior that reflect the operation of spin selection rules and the importance of intersystem crossing processes in Biradical chemistry.
Abstract: The technique of laser flash photolysis and equipment required for using the technique are briefly described The possibilities, use, and limitations of the laser photolysis technique to studies in the area of biradical reactions are discussed The biradicals discussed were generated as intermediates in the Norrish type II reactions and the photoenolization of o-alkyl-substituted carbonyl compounds Values for representative lifetimes for biradicals derived from these reactions are tabulated Hydrogen abstraction studies were carried out with molecules with very labile hydrogen atoms, and values for rate constants for these reactions are tabulated The interaction of biradicals with paramagnetic species such as oxygen, nitroxides, and copper(II) complexes were studied by the laser technique, and the reactions show characteristic behavior that reflects the operation of spin selection rules and the importance of intersystem crossing processes in biradical chemistry (BLM)
136 citations
87 citations
TL;DR: A quantitative product analysis has shown that these inhibitors react by hydrogen abstraction from a thermally generated styrene dimer (1phenyl-1,2,3,9-tetrahydronaphthalene) and to a minor extent by addition to the double bond of styrene monomer as mentioned in this paper.
Abstract: The efficient free radical scavengers 1,1,3,3-tetramethylisoindolinyl 2-oxy and 2,2,6,6-tetramethylpiperidinyl-1-oxy (nitroxides) disappear in styrene at 100°C with near zero order kinetics but at rates which are some 20 times higher than the known rate of initiation of thermal polymerization in the absence of scavenger A quantitative product analysis has shown that these inhibitors react by hydrogen abstraction from a thermally generated styrene dimer (1-phenyl-1,2,3,9-tetrahydronaphthalene) and to a minor extent by addition to the double bond of styrene monomer
84 citations
TL;DR: In this article, a theoretical investigation of the energetics and dynamics of the O(1D)+H2 reaction is reported, and two different valence bond diatomics-in-molecules potential energy surfaces were used which differed only in the presence or absence of a small barrier to the C2v approach.
Abstract: A theoretical investigation of the energetics and dynamics of the O(1D)+H2 reaction is reported. Two different valence bond diatomics‐in‐molecules potential energy surfaces were used which differed only in the presence or absence of a small barrier to the C2v approach. The results of quasiclassical trajectory calculations were completely different on the two surfaces and showed that the dynamics of this exothermic reaction are sensitive to features of the surface at large internuclear distances. Reactions were found to occur by two possible mechanisms. In one mechanism, the oxygen atom abstracts a hydrogen atom from the end of the molecule in a direct reaction. Alternatively, the oxygen atom inserts into the H–H bond to form a collision complex which subsequently breaks apart. At all collision energies, the vibrational distribution of products from insertion/decomposition events is statistical while that of abstraction events is centered about v′ = 2. An inversion in the total populations of the levels v′...
83 citations
TL;DR: In this article, the proportion of each of these processes, as well as the fraction of tert-butoxy radicals that fragment to give methyl radicals, has been determined by analysis of the products that result on trapping the transient carbon-centered radicals with 1,1,3,3-tetramethylisoindoline-2-oxyl.
Abstract: Tert-butoxy radicals, derived from the thermal decomposition of di-tert-butyl peroxalate at 60°C, react with methyl, ethyl, and n-butyl methacrylate by double-bond addition and by hydrogen abstraction from the α-methyl and ester alkyl functions. The proportion of each of these processes, as well as the fraction of tert-butoxy radicals that fragment to give methyl radicals, has been determined by analysis of the products that result on trapping the transient carbon-centered radicals with 1,1,3,3-tetramethylisoindoline-2-oxyl.
67 citations
TL;DR: In this article, it was shown that the carbon-centred radicals formed by interaction of cumyloxyl with the respective monomers were trapped as stable adducts of 1,1,3,3-tetramethyl-isoindolin-2-yloxymethyloxyl.
Abstract: Cumyloxy (1-methyl-1-phenylethoxy) radicals have been generated by thermolysis (60o) of dicumyl hyponitrite in methyl methacrylate and styrene. The carbon-centred radicals formed by interaction of cumyloxyl with the respective monomers were trapped as stable adducts of 1,1,3,3-tetramethyl-isoindolin-2-yloxyl. Extensive hydrogen atom abstraction and methyl radical generation as well as double-bond addition were observed in methyl methacrylate. Styrene underwent only double-bond addition by both cumyloxy and methyl radicals. Some possible implications of these results for polymer structure are discussed. A kinetic study of the decomposition of dicumyl hyponitrite in cyclohexane at various temperatures gave k=7.7 × 1014exp(-13600/T) s-1 for the rate constant. Rate constants for the addition of cumyloxyl to methyl methacrylate (k ≈ 2 × 104 dm3 mol-1 s-1) and styrene (k≈2 × 105 dm3 mol-1 s-1) at 60ohave been estimated.
63 citations
TL;DR: In this article, Ab initio molecular orbital theory is used to study geometrics and energies of hydrogen-bonded complexes between hydrogen fluoride, hydrogen chloride and acetylene, ethylene, as proton acceptors.
56 citations
TL;DR: No evidence for the formation of carbon-centered radicals was found in comparable experiments with cysteine and 2-mercaptopropionylglycine, and the reaction of OH with glutathione in neutral and alkaline aqueous solutions has been studied by pulse radiolysis.
Abstract: SJOBERG, L., ERIKSEN, T. E., AND REVESZ, L. The Reaction of the Hydroxyl Radical with Glutathione in Neutral and Alkaline Aqueous Solution. Radiat. Res. 89, 255-263 (1982). The reaction of OH with glutathione (y-glu-cys-gly) in neutral and alkaline aqueous solutions has been studied by pulse radiolysis. In addition to the sulfur-centered GS.(GSSG-.) radical formed by electron transfer or hydrogen abstraction from GS- (GSH), at least one carbon-centered radical is formed with pH-dependent yield by hydrogen abstraction from the y carbon or the amino group on the 'y-glutamyl moiety. The latter radical is transformed in a first-order reaction most probably to a carbon-centered radical on the cysteine group. No evidence for the formation of carbon-centered radicals was found in comparable experiments with cysteine and 2-mercaptopropionylglycine.
54 citations
TL;DR: By molecular beam-laser induced fluorescence experiments, this article probed the nascent internal state distribution and dynamic energy thresholds of OH formed by the abstraction of hydrogen atoms from alkyl substituted olefins and alkynes.
Abstract: By molecular beam‐laser induced fluorescence experiments, we have probed the nascent internal state distribution and dynamic energy thresholds of OH formed by the abstraction of hydrogen atoms from alkyl substituted olefins and alkynes. Low thresholds are obtained, especially for olefins, suggesting that this is an important mechanism in high temperature combustion. OH rotational excitation is small and implies a collinear transition state similar to that observed previously for O(3P) reaction with saturated hydrocarbons. OH vibrational excitation is also low for the olefins and suggests that considerable internal excitation of the allyl or methyl allyl radicals occur in the reactions.
TL;DR: A review of the types of hydrogen bonds and discussion of the application of spectroscopic and diffraction methods to studies of moderate and strong hydrogen bonds can be found in this article, where the authors also discuss the applications of diffraction and spectroscopy in the field of hydrogen bonding.
Abstract: A review of the types of hydrogen bonds and discussion of the application of spectroscopic and diffraction methods to studies of moderate and strong hydrogen bonds.
TL;DR: In this paper, a free-radical chain decomposition mechanism involving steps 5 and 6, in which k/sub 6/>>k/sub 5/(1) rather than from a concerted retro-ene cleavage was proposed.
Abstract: Cracking of 1,3-diphenylpropane (1) at 345-425/sup 0/C to give toluene and styrene proceeded much more rapidly than expected from the strength of its weakest C-C bond. Styrene was rapidly consumed in secondary reactions, one of which was addition to 1 to form 1,3,5-triphenylpentane. Toluene product from 1-1,1,3,3-d/sub 4/ contained no detectable deuterium in the aromatic ring. Combination of these experimental data with thermochemical kinetic estimation procedures demonstrates that the rate ''acceleration'' results from a free-radical chain decomposition mechanism involving steps 5 and 6, in which k/sub 6/>>k/sub 5/(1), rather than from a concerted retro-ene cleavage. The failure of such a chain to develop for 1,2-diphenylethane is a consequence of the dependence of ..delta..H/sup 0/ for radical ..beta.. scission on structure. Cracking of 1,4-diphenylbutane (2) gave both toluene plus allylbenzene and ethylbenzene plus styrene. The ratio between these competitive pathways increased nonlinearly with concentration from 0.18/sub 5/ at 100-110 kPa to 0.82 in the neat liquid. The key step is the interconversion of 1,4-diphenyl-1-butyl radical and its 2-isomer by hydrogen abstraction from 2, a process which is competitive with ..beta.. scission. Thermochemical kinetic estimates lead to a set of rate constants which are consistent with the observed product ratio behavior. Thesemore » ..cap alpha..,..omega..-diphenylalkanes, Ph(CH/sub 2/)/sub n/Ph, serve as models for aliphatic bridges between aromatic units in coal. The implications of the demonstrated chain character of their thermolysis when n..-->..>3 for modeling the thermal decomposition of coal are discussed.« less
01 Jan 1982
TL;DR: In this article, the authors measured stable species and free radicals using molecularbeam mass spectrometry in the secondary reaction zone of a near-sooting (=1.8) 2.67 kPa benzene-oxygen-argon flame.
Abstract: Mole fraction profiles of stable species and free radicals have been measured using molecularbeam mass spectrometry in the secondary reaction zone of a near-sooting (=1.8) 2.67 kPa benzene-oxygen-argon flame. From the measurement of H, OH, O2, H2 and H2O mole fractions and the calculation of the O-atom mole fraction from a steady-state analysis Rxns. 2, 3 and 8 are near equilibrium in the presence of hydrocarbons. Rxn. 1 does not reach equilibrium. H+O2OH+O Rxn. 1 O+H2OH+H Rxn. 2 O+H2OOH+OH Rxn. 3 H+H2OOH+H2 Rxn. 8 Three types of hydrocarbon (HC) reactions were found to be equilibrated: (I) HC's with HC free radicals via hydrogen abstraction reactions, (II) polyacetylenes with C2H2 and H2, (III) odd-numbered HC radicals with C2H2 and H2. From these equilibria, ΔHf300o(C3H2)=531±13 kJ/mol and ΔHf300o (C5H3)=568±13 kJ/mol. From the concept of a HC pool, the decay of equilibrated hydrocarbons is found to be dominated by reactions of C2H2 and C4H2 with O and OH. A rate coefficient of k=1.3±0.3×1012 cm3 mol−1 s−1 is obtained for the OH+C2H2 reaction between 1700 and 1900 K.
TL;DR: In this article, it was shown that the aliphatic amine assisted photodechlorinations of chlorides of the benzene, naphthalene, and biphenyl series take place mainly from the triplet excited state.
Abstract: Kinetic arguments show that the aliphatic amine assisted photodechlorinations of chlorides of the benzene, naphthalene, and biphenyl series take place mainly from the triplet excited state. Deuterium labeling studies have been used to determine the origin of the hydrogen atom which replaces chlorine when 4-chlorobiphenyl is photoreduced. Three pathways are inferred: hydrogen abstraction from the solvent and protonation both within the exciplex (or radical ion pair) and by external proton donors.
TL;DR: In this article, the photolysis of carbon tetrachloride in the presence of a number of alkanes has been investigated in the gas phase and the results obtained from the experiments were those expected from a chain reaction in which trichloromethyl radicals abstract hydrogen atoms from the alkane.
Abstract: The photolysis of carbon tetrachloride in the presence of a number of alkanes has been investigated in the gas phase. The products obtained from the photolysis experiments were those expected from a chain reaction in which trichloromethyl radicals abstract hydrogen atoms from the alkane. The data have been used to determine Arrhenius parameters for hydrogen abstraction from the series of alkanes CH4, C2H6, C3H8, and i-C4H10 by trichloromethyl radicals,
The rate data obtained are used to explain why termination reactions involving alkyl radicals become less significant as the alkane becomes more complex.
TL;DR: This paper showed that pentadienyl-and allyl-type radicals have been observed by e. s. r. spectroscopy from linoleate and oleate derivatives, and delocalised radicals have also been observed from other lipid derivatives including triacylglycerols.
Abstract: Hydrogen abstraction from linoleate and oleate gives rise to pentadienyl-and allyl-type radicals, respectively, Which have been observed by e. s. r. spectroscopy; delocalised radicals have also been observed from other lipid derivatives including triacylglycerols.
TL;DR: In this paper, the thermally unstable "UO 2 R 2 )-type dichlorodioxouranium (VI) species was studied and compared with the corresponding alkane and alkene and UO 2, when R = i-propyl, n-butyl, and t-Butyl.
TL;DR: In this paper, the source of the hydrogen atom has been identified as a reduction of the corresponding cations, and the resulting reduction reactions are rationalised in terms of the nature of the HOMO in the intermediate radical.
TL;DR: In this article, the authors probed nascent internal state distribution and dynamic energy thresholds of OH formed in the reactions of O(3P) with amines, and showed that the mechanism for OH formation is direct abstraction from a C-H bond.
Abstract: Using crossed molecular beam‐laser induced fluorescence experiments, we have probed nascent internal state distribution and dynamic energy thresholds of OH formed in the reactions of O(3P) with amines. The results imply that the mechanism for OH formation is direct abstraction from a C–H bond. This is contrary to an earlier suggestion that OH is formed as a result of an addition mechanism.
TL;DR: In this article, photolysis of N-ω-alkoxyalkylphthalimides gave the intramolecularly cyclized compounds, oxazolo [4, 3-a] isoindoles 2a-g, pyrrolo [2, 1-a]-isoindole-1-spiro-1'-cycloalkanes 2k-n and 3, 4-dihydro-2-benzazepine-1, 5 (2H)-dione 3, via δ-hydrogen abstraction and
Abstract: Photolysis of N-ω-alkoxyalkylphthalimides 1 gave the intramolecularly cyclized compounds, oxazolo [4, 3-a] isoindoles 2a-g, pyrrolo [2, 1-a] isoindoles 6i-j, oxazolo [4, 3-a]-isoindole-1-spiro-1'-cycloalkanes 2k-n and 3, 4-dihydro-2-benzazepine-1, 5 (2H)-dione 3, via δ-hydrogen abstraction and/or two-fold Norrish type II processes.
TL;DR: The stereochemistry of the autoxidation of hex-1-ene, cis-and transhex-2-ene and trans-hex-3-ene has been determined by the reduction of the hydroperoxides produced and analysis of the resulting allylic alcohols as discussed by the authors.
Abstract: The stereochemistry of the autoxidation of hex-1-ene, cis- and trans-hex-2-ene, cis- and trans-hex-3-ene, and of the three geometrical isomers of hepta-2,5-diene, has been determined by the reduction of the hydroperoxides produced and analysis of the resulting allylic alcohols. The relative proportions of the isomeric hydroperoxides are explicable in terms of the conformations of the parent olefins which are capable of giving delocalised radicals on hydrogen abstraction.
TL;DR: Fluorescence quenching experiments indicate that energy transfer occurs from cumene excited at 254 nm to cumene hydroperoxide, which is the main photoproduct of polystyrene as discussed by the authors.
TL;DR: In this article, it was shown that radicals produced from benzoyl peroxide and diisopropyl peroxydicarbonate react with methyl methacrylate mainly by addition to the less substituted end of the double bond (tail addition).
Abstract: Contrary to a recent report, radicals produced from benzoyl peroxide and diisopropyl peroxydicarbonate react with methyl methacrylate mainly by addition to the less substituted end of the double bond (tail addition). Benzoyloxy radicals do give head addition, but only to a small extent relative to tail addition (ratio 5∶66). With both initiators hydrogen abstraction from monomer is only a minor process (⩽1%). These results were obtained by analysis of the products formed when radicals are trapped by nitroxides.
TL;DR: In this paper, a redox radical mechanism is proposed and the selectivity of the hydrogen abstraction by t-butoxy radicals and reduction of α-ketoalkyl radical by titanous ions is discussed.
TL;DR: In this article, the title compounds undergo hydrogen abstraction from the solvent via a π,π* excited singlet state as well as skeletal rearrangement via a R(3s) Rydberg excited state.
Abstract: Upon direct irradiation at 185 nm, the title compounds undergo hydrogen abstraction from the solvent via a π,π* excited singlet state as well as skeletal rearrangement via a π,R(3s) Rydberg excited state.