Showing papers on "Hydrogen atom abstraction published in 1972"
TL;DR: A series of alcohols and amines have been oxidised at oxide-covered nickel, silver, copper, and cobalt anodes in aqueous alkaline solutions as mentioned in this paper, and it was shown that the mechanism of these oxidations involves hydrogen abstraction from the substrate by an oxide species rather than direct electron transfer to the anode.
Abstract: A series of alcohols and amines have been oxidised at oxide-covered nickel, silver, copper, and cobalt anodes in aqueous alkaline solutions. The kinetics of these electrode processes have been studied and it is shown that the mechanism of these oxidations involves hydrogen abstraction from the substrate by an oxide species rather than direct electron transfer to the anode. The mechanism put forward is compared with those commonly suggested for the chemical reactions of transition-metal oxides and for heterogeneous catalysis.
313 citations
160 citations
TL;DR: It is concluded from the percentage retention of the tritium label in the main products formed, that these lipoxygenases have opposite stereospecificity in the hydrogen abstraction at carbon n-8: Lipoxygenase from corn germs mainly removes the DR(n-8) hydrogen, whereas lipoxyGENase from soya beans removes the LS(n) hydrogen.
124 citations
118 citations
TL;DR: The rates of formaldehyde photodecomposition into hydrogen and formyl radicals and hydrogen and carbon monoxide molecules in sunlightirradiated atmospheres have been estimated from extinction data and photochemical results and should prove useful in the development of models for the chemical changes that take place in the polluted atmosphere.
Abstract: The rates of formaldehyde photodecomposition into hydrogen and formyl radicals and hydrogen and carbon monoxide molecules in sunlightirradiated atmospheres have been estimated from extinction data and photochemical results. These data should prove useful in the development of models for the chemical changes that take place in the polluted atmosphere.
112 citations
TL;DR: The photoreactivity of benzophenone in water has been reinvestigated in this article, where it is suggested that hydrogen abstraction from water occurs to give free OH radicals which then attack benzphenone to give a cyclohexadienyl radical.
Abstract: Phosphorescence has been observed from oxygen-free aqueous solutions of benzophenone and acetophenone. In the case of benzophenone the phosphorescence is strongly self-quenched. Rate constants for quenching of triplet benzophenone by various species have been measured.The photoreactivity of benzophenone in water has been reinvestigated. Photolysis does occur, the quantum yield being low and somewhat irreproducible. Benzopinacol is a product of the photolysis in oxygen-free solution, while in aerated solution hydroxybenzophenones are formed with a very low quantum yield.Flash photolysis experiments have characterized the triplet-triplet absorption of benzophenone in aqueous solution and show that the ketyl radical and another radical are intermediates in the reaction. It is suggested that hydrogen abstraction from water occurs to give free OH radicals which then attack benzophenone to give a cyclohexadienyl radical. The energetics of this process are considered.
82 citations
66 citations
TL;DR: In this paper, a competition reaction between 2,6-di-t-butylphenol (I) and a singlet oxygen acceptor (linalool), quenching by a quencher (β-carotene), and the effect of concentrations of I were examined.
64 citations
54 citations
54 citations
TL;DR: In this paper, the primary photochemical reactions of carbonyl compounds commonly used as photoinitiators were investigated and the difference in the suitability of the radicals for chain initiation was discussed.
Abstract: The present article deals with the primary photochemical reactions of carbonyl compounds commonly used as photoinitiators. It is shown that radical formation results mainly from three processes, i.e. hydrogen abstraction, β-cleavage, and α-cleavage. The difference in the suitability of the radicals for chain initiation is discussed.
TL;DR: The relative photochemical reactivity of α-diketones, in particular, 9,10-phenanthraquinone, 1, 2,2-naphthoquinone and acenaphthoequinone was investigated in hydrogen donating solvents as discussed by the authors.
Abstract: The relative photochemical reactivity of α-diketones, in particular, 9,10-phenanthraquinone, 1,2-naphthoquinone, acenaphthoquinone, benzil, 4,4′-dimethylbenzil, 2,4,6-trimethylbenzil, 2,5,2′,5′-tetramethylbenzil, 2,3,5,6-tetramethylbenzil, 2,4,6,2′,4′,6′-hexamethylbenzil, phenylglyoxal, 2,5-dimethylphenylglyoxal, and 2,4,6-trimethylphenylglyoxal was investigated in hydrogen donating solvents. Type of the product and relative reactivity differ widely according to the structure of α-dike tones. Whereas 9,10-phenanthraquinone gives 1,4-adduct (V) in a hydrogen donating solvent (THF), 2,5,2′,5′-tetramethylbenzil gives 2-hydroxy-2-(2′,5′-dimethylphenyl)indanone (VII) via intramolecular hydrogen abstraction in nearly quantitative yield. No photochemical reaction of 2,4,6-trimethylbenzil or 2,3,5,6-tetramethylbenzil could be observed in the same solvent even under a long irradiation.
TL;DR: The extent of hydrogen atom exchange in the reaction, CH3(+) + CH4 yields C2H5+H2, was determined by examining the product distribution for the reactions CH3++CD4 and CD3+CH4 as a function of relative kinetic energy from thermal energies to 10 eV.
Abstract: The extent of hydrogen atom exchange in the reaction, CH3(+) + CH4 yields C2H5(+) + H2, is determined by examining the product distribution for the reactions CH3(+) + CD4 and CD3(+) + CH4 as a function of relative kinetic energy from thermal energies to 10 eV. It is found that the reaction of CH4(+) with the parent neutral proceeds both via proton transfer and hydrogen abstraction accompanied by approximately 10% hydrogen atom exchange during the reaction.
TL;DR: In this paper, the reaction of organic halides with carbonyl compounds in the presence of lithium or sodium and with tetrahydrofuran as solvent have been studied.
Abstract: The reactions of organic halides with carbonyl compounds in the presence of lithium or sodium and with tetrahydrofuran as solvent have been studied. When lithium is used alcohols are formed in high yield which in many cases exceed those obtained by the analogous Grignard reaction. The process involves the intermediate formation of organo-lithium species. With sodium, the yield of alcohol is significantly reduced and with carbonyl compounds possessing α-hydrogen atoms, hydrogen abstraction by the intermediate organo-sodium species predominates. The effect of the addition of electron-transfer reagents such as naphthalene or biphenyl to the sodium system has been studied and the yields of alcohols have been shown to increase with the concentration of additive present.
TL;DR: In this article, two T-T′ absorption systems of chloranil were obtained with well-resolved vibrational structures in trichlorotrifluoroethane and tetrahydrofuran.
Abstract: Transient absorption spectra have been obtained by the flash photolysis of chloranil in various organic solvents. In trichlorotrifluoroethane, two T-T′ absorption systems of chloranil were obtained with well-resolved vibrational structures. In tetrahydrofuran, on the other hand, absorption spectra mostly consist of semiquinone radical formed by the hydrogen abstraction from solvent. In benzene and in acetone, the first T-T′ absorption system was much more diffuse and was accompanied by a weak, broad absorption at longer wavelength (λ>550 nm) which might be assigned to a charge transfer absorption from triplet chloranil as acceptor and the solvent molecule as donor. In acetone and in methanol, it has also been found that there is an equilibrium between semiquinone radical and semiquinone anion.
TL;DR: In this article, the rate constants for decarboxylation of several acids of the type RXCH2CO2H (X = O, S, and NH), sensitised by benzophenone and tetrachloro-p-benzoquinone have been determined.
Abstract: The rate constants for the decarboxylation of several acids of the type RXCH2CO2H (X = O, S, and NH), sensitised by benzophenone and tetrachloro-p-benzoquinone have been determined. The reactions are considered as occurring via exciplex formation between the carbonyl compound and the acid, and in agreement with this hypothesis, the published values of rate constants for the reaction of triplet benzophenone with substituted hydrocarbons (RXCH3) are very similar to those determined for reaction with the corresponding carboxylic acid. In addition, the rate constants for decarboxylation are in the order expected from a consideration of the ionisation potentials of their corresponding substituted hydrocarbon (RXCH3). The rate constants for reaction with the quinone are higher than those for the corresponding reactions with benzophenone. Decarboxylation of (phenylthio)acetic acid in acetonitrile solution is acid catalysed whereas in benzene solution, acids slightly retard the reaction. This reaction is also quenched by methyl phenyl sulphide. Attention is drawn to the fact that the inefficiency of photoreduction of benzophenone by substituted hydrocarbons (RXCH3) can stem from the hydrogen abstraction reaction being reversible, as well as being due to exciplex formation.
TL;DR: In this paper, the hydrogen isotope exchange rates of α-deuterio- and α-tritiocyclopropanes with electron-withdrawing substituents and the corresponding open 2-substituted propanes have been measured in solutions of sodium methoxide in methanol.
TL;DR: In this article, the UHF LCAO MO GTO framework was used to evaluate the effects of addition of polarization functions to both the hydrogen and carbon basis sets for exchange and abstraction reactions of H + CH4.
TL;DR: In this paper, cyclic thiocarbonyl imines the 4-aryl-1.3.2-oxathiazolium 5-olates (2) with dimethyl acetylenedicarboxylate and propiolic ester to give initially adducts which then eliminate carbon dioxide to form the isothiazoles 3-7.
Abstract: Als cyclische Thiocarbonyl-imine vereinigen sich 4-Aryl-1.3.2-oxathiazolium-5-olate (2) bei 60–100° mit Acetylendicarbonester und Propiolester unter Kohlendioxid-Freisetzung zu den Isothiazolen 3–7. Den Cycloadditionen der Oxathiazolium-5-olate mit Maleinester, Zimtester und Styrol folgen CO2- und Wasserstoffabgabe, wiederum zu Isothiazol-Derivaten (3, 15–19) fuhrend.
Isothiazoles by Reaction of 1.3.2-Oxathiazolium 5-olates with CC-Multiple Bonds
As cyclic thiocarbonyl imines the 4-aryl-1.3.2-oxathiazolium 5-olates (2) combine at 60–100° with dimethyl acetylenedicarboxylate and propiolic ester to give initially adducts which then eliminate carbon dioxide to form the isothiazoles 3–7. The cycloadditions with maleic ester, cinnamic ester, and styrene are followed by CO2- and hydrogen abstraction, again leading to isothiazoles (3, 15–19).
TL;DR: In this article, a series of pre-calculated kinetic parameters are reported in order to allow the fast estimation of rate constants avoiding detailed calculations, and the possibility of using the method for carbonyl compounds having low lying π-π* triplets is discussed.
Abstract: By application of a novel method based on the Bond-Energy–Bond-Order method, a series of kinetic parameters for reactions involving hydrogen abstraction by carbonyl triplets have been calculated. In principle the method is only applicable in the gas-phase; however, a good agreement with experiment is generally observed in reactions involving n–π* triplets in non-polar solvents. The possibility of using the method for carbonyl compounds having low lying π–π* triplets is discussed. A series of pre-calculated kinetic parameters are reported in order to allow the fast estimation of rate constants avoiding detailed calculations.
TL;DR: In this article, it was suggested that hydrogen abstraction from monomer is the origin of photoinitiation under the present conditions, and it has been suggested that similar hydrogen abstraction is also possible from a monomer in the presence of organic halide.
Abstract: Os3(CO)12 and Re2(CO)10 when irradiated by light of λ= 365 nm initiate the polymerization of methyl methacrylate and acrylonitrile in the absence of organic halide; species arising from photoexcitation of the carbonyls are shown to abstract hydrogen from hydrocarbons to form the corresponding free radicals, and it is suggested that similar hydrogen abstraction from monomer is the origin of photoinitiation under the present conditions.
TL;DR: In this article, a critical comparison is made between a theoretical model for photochemical reactions based on their analogy with radiationless transitions and the experimental data on hydrogen abstraction by excited ketones in solution.
TL;DR: In this article, the authors measured the kinetic isotope effects for the hydrogen abstraction reactions of fluorine atoms with H2, CH4 and CHCl3 using indirect competitive methods.
Abstract: Kinetic isotope effects for the hydrogen abstraction reactions of fluorine atoms with H2, CH4 and CHCl3 have been measured by indirect competitive methods. The relative rate constants are given by k(CHCl3)/k(CDCl3)= 0.81 ± 0.25 exp[(620 ± 50)/RT], k(H2)/k(D2)= 1.5 ± 0.4 exp[(130 ± 300)/RT], k(CH4)/k(CD4)= 1.0 ± 0.3 exp[(230 ± 200)/RT]. The result for k(H2)/k(D2) agrees with that previously measured. These relatively small kinetic isotope effects are compared with rate parameters calculated from activated complex theory and classical trajectory analysis. Hydrogen atom transfer by quantum mechanical tunnelling is apparently unimportant.