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Showing papers on "Hydrogen atom abstraction published in 1985"


Journal ArticleDOI
TL;DR: The formation of surface-generated gas-phase radicals during the reactions of methane, ethane, ethylene, and propylene over Bi/sub 2/O/sub 3/,..gamma..-Bi/sub O/Sub 3/XMoO/XSub 3/, PbO, MgO, and Li/MgO was examined by EPR matrix isolation spectroscopy as discussed by the authors.
Abstract: The formation of surface-generated gas-phase radicals during the reactions of methane, ethane, ethylene, and propylene over Bi/sub 2/O/sub 3/, ..gamma..-Bi/sub 2/O/sub 3/ x MoO/sub 3/, PbO, MgO, and Li/MgO was examined by EPR matrix isolation spectroscopy. Allyl radicals were detected during the reaction of propylene over all of the oxides examined. Gas-phase methyl and ethyl radicals were detected during the reactions of methane and ethane, respectively, over MgO and Li/MgO while Bi/sub 2/O/sub 3/, ..gamma..-Bi/sub 2/O/sub 3/ x MoO/sub 3/, and PbO were essentially inactive. Gas-phase vinyl radicals were not detected during the reaction of ethylene over any of the oxides. These differences in reactivity are attributed to differences in reactivity of the oxide ions on these surfaces towards hydrogen atom abstraction. 28 references, 1 figure.

150 citations


Journal ArticleDOI
TL;DR: In this paper, a comprehensive theoretical study has been made of the energetics of the important pathways involved in the reaction of hydrogen atoms with hydrogen cyanide, including the hydrogen abstraction reaction and the hydrogen addition reaction.
Abstract: A comprehensive theoretical study has been made of the energetics of the important pathways involved in the reaction of hydrogen atoms with hydrogen cyanide. For each reaction ab initio GVB‐CI calculations were carried out to determine the structures and vibrational frequencies of the reactants, transition states, and products; then POL‐CI calculations were carried out to more accurately estimate the electronic contribution to the energetics of the reactions. The hydrogen abstraction reaction is calculated to be endoergic by 24 kcal/mol [expt. ΔH (0 K)=16–19 kcal/mol] with a barrier of 31 kcal/mol in the forward direction and 6 kcal/mol in the reverse direction. For the hydrogen addition reactions, addition to the carbon atom is calculated to be exoergic by 19 kcal/mol with a barrier of 11 kcal/mol, while addition to the nitrogen center is essentially thermoneutral with a barrier of 17 kcal/mol. Calculations were also carried out on the isomerization reactions of the addition products. The cis→trans isome...

98 citations



Journal ArticleDOI
TL;DR: The results strongly suggest that the formation of both uracil and Uracil propenal is the consequence of a rate-determining 4'-carbon-hydrogen bond cleavage and of an O2-dependent partitioning of the intermediate produced by this cleavage.
Abstract: When poly(dA-[4'-3H]dU) was degraded by activated bleomycin under a variety of conditions, 50 +/- 10% of the deoxyuridine residues were converted to uracil and uracil propenal, paralleling observations made with DNA. By manipulation of the concentration of O2 in solution, the relative ratio of uracil propenal to uracil could be varied between 0.03 for anaerobic activation and 7.0 for activation at 3 atm of O2. Tritium selection effects on 4'-hydrogen abstraction were also measured under these conditions and found to range from 7.2 to 12.5. These results strongly suggest that the formation of both uracil and uracil propenal is the consequence of a rate-determining 4'-carbon-hydrogen bond cleavage and of an O2-dependent partitioning of the intermediate produced by this cleavage.

93 citations




Journal ArticleDOI
John D. Coyle1

82 citations


Journal ArticleDOI
TL;DR: In this article, the reactions of photochemically generated Cl(2PJ) atoms with a number of fluorohydrocarbons have been investigated in the temperature range 8-95°C by the competitive photochlorination technique using CH4 as a primary standard.
Abstract: The reactions of photochemically generated Cl(2PJ) atoms with a number of fluorohydrocarbons have been investigated in the temperature range 8–95 °C by the competitive photochlorination technique using CH4 as a primary standard. Relative and absolute rate parameters are reported for CH3F, CH2F2, CH3CH2F, CH2FCH2F, CH3CHF2, CH3CF3, CH2FCHF2, CHF2CHF2, and several auxiliary reactions including CH3Cl, C2H6, and C3H8. The internal competition for hydrogen abstraction in asymmetric fluorethanes is examined in detail. The reactivity trends are discussed and it is found that the activation energies in the fluoromethane series correlate with the known C–H bond dissociation energies. The hydrogen reactivity in the fluoroethane series for which a sufficient data base of DH°(C–H) values is not available is best rationalized in terms of inductive effects and resonance interactions.

81 citations


Journal ArticleDOI
TL;DR: In this paper photolysis of several nitroamines, cianamines, and phosphoroamidates in the presence of iodosobenzene diacetate (IBDA) and iodine leads to neutral aminyl radicals which undergo intramolecular hydrogen abstraction to produce epimine compounds with yields that are favorably compared with those obtained with the system lead tetraacetate and iodine.

80 citations


Journal ArticleDOI
TL;DR: In this paper, the photocatalytic activity of anatase TiO2 depended significantly on the amount of metal or metal oxide present; the effect on the activity increased in the order platinum black ≫ platinum powder > ruthenium dioxide.
Abstract: Photoirradiation (λex > 300 nm) of Ar-purged aqueous propan-2-ol solution gave hydrogen and acetone in the presence of platinum- and/or ruthenium dioxide-loaded TiO2. The photocatalytic activity of anatase TiO2 depended significantly on the amount of metal or metal oxide present; the effect on the activity increased in the order platinum black ≫ platinum powder > ruthenium dioxide. The photocatalytic activity of rutile TiO2 was negligible even when loaded with platinum black. The effective wavelengths for the photocatalytic dehydrogenation of propan-2-ol were below ca. 390 nm, in agreement with the u.v. absorption spectrum of anatase TiO2. In a similar way primary, secondary and tertiary aliphatic alcohols underwent photocatalytic oxidation, accompanied by hydrogen liberation, by the platinized TiO2. The primary and secondary alcohols gave the corresponding carbonyl derivatives, while 2-methylpropan-2-ol and acetone gave dimeric products accompanied by stoichiometric hydrogen evolution. The initial rate of dehydrogenation in these photocatalytic systems was in proportion to the rate constants of hydrogen abstraction by hydroxyl radical in the homogeneous systems.

75 citations


Journal ArticleDOI
TL;DR: In this paper, the energy properties of hydrogen abstraction reactions with R, X≡H, CH3, NH2,OH, and F have been studied at the abinitio 6-31G -UHF level.
Abstract: Hydrogen abstraction reactions with R, X≡H, CH3, NH2,OH, and F have been studied at the abinitio 6-31G – UHF level. However, energetic properties were computed at the CI level. Rate constants and A...

Journal ArticleDOI
TL;DR: It has been established that the horseradish peroxidase/O2/isobutyraldehyde (IBAL) system leads to triplet acetone and formic acid formation followed by phosphorescence of the tripleT acetone, and many of the mechanistic details are established.

Journal ArticleDOI
TL;DR: Several oxygen-substituted o-nitrobenzylic compounds in THF solution were studied by photo-conditional transient spectroscopy as mentioned in this paper, and the o-quinonoid intermediate resulting from intramolecular H abstraction was observed in those compounds which undergo efficient reaction.
Abstract: Several oxygen-substituted o-nitrobenzylic compounds in THF solution were studied by picosecond transient spectroscopy. The o-quinonoid intermediate resulting from intramolecular H abstraction was observed in those compounds which undergo efficient reaction. In the case of phenyl o-nitrobenzyl ether and p-cyanophenyl o-nitrobenzyl ether, both the triplet excited state and the o-quinonoid were observed at early times. For these two compounds, the o-quinonoid intermediate is formed from the singlet excited state at a rate much faster than triplet decay. 18 references, 4 figures.

Journal ArticleDOI
TL;DR: It is possible to formulate a reaction scheme in which the carbon- centered radical at C-5' is an intermediate in the formation of the various DNA damage products found under both aerobic and anaerobic conditions.
Abstract: Thiol-activated neocarzinostatin chromophore abstracts tritium from the 5', but not from the 1' or 2' positions of deoxyribose in DNA and incorporates it into a stable, non-exchangeable form. The abstracted tritium remains covalently associated with the chromophore or its degradation product after treatment with acid or alkali, respectively. Drug activation and the consequent hydrogen abstraction reaction, presumably generating a carbon-centered radical at C-5', do not require molecular oxygen but have a dose-dependent relation with thiol. Under aerobic conditions, where base release and DNA strand breaks with nucleoside 5'-aldehyde at the 5'-ends are produced, hydrogen abstraction from C-5' parallels these parameters of DNA damage. It is possible to formulate a reaction scheme in which the carbon- centered radical at C-5' is an intermediate in the formation of the various DNA damage products found under both aerobic and anaerobic conditions.


Journal ArticleDOI
TL;DR: In this article, a tri-n -butyltin hydride (deuteride) reaction with carbon-centered 5-hexen-1-yl type radicals is described.

Journal ArticleDOI
TL;DR: The reaction of singlet oxygen with α,β-unsaturated esters shows a general preference for hydrogen abstraction on the alkyl group geminal to the ester.

Journal ArticleDOI
TL;DR: In this paper, it was shown that the peroxide peroxide bond cleavage is a key intermediates in the decomposition of the original alkane and that the resulting radicals stabilize themselves either as ketones or as HO 2 radicals.

Journal ArticleDOI
TL;DR: The results are consistent with a mechanism for dopamine beta-hydroxylase in which a hydrogen atom is abstracted to form a benzylic radical, which then partitions between hydroxylation and enzyme inactivation.
Abstract: A series of ring-substituted 3-phenylpropenes has been examined as mechanism-based inhibitors for the copper protein dopamine beta-hydroxylase. p-HO-, p-CH/sub 3/O-, m-HO-, m-CH/sub 3/O-, p-Br-, and p-CN-substituted phenylpropenes all inactivate the enzyme under turnover conditions, requiring ascorbate and oxygen. Replacement of the benzylic hydrogens in 3-(p-hydroxyphenyl)propene with deuterium results in a kinetic isotope effect of 2.0 on kinact/KO/sub 2/ but in no effect on the partition ratio, V /sub max//kinact, consistent with a stepwise mechanism for hydrogen abstraction and oxygen insertion. The partition ratio is unchanged in the pH range from 4.5 to 7.1. Determination of the kinetics of inactivation and the partition ratios for each of these ring-substituted phenylpropenes has allowed determination of the respective V/KO/sub 2/ values. A linear free energy plot of these values as a function of sigma+ gives a rho value of -1.2, while the partition ratios show only a slight decrease upon going electron-withdrawing groups. The results are consistent with a mechanism for dopamine beta-hydroxylase in which a hydrogen atom is abstracted to form a benzylic radical, which then partitions between hydroxylation and enzyme inactivation.

Journal ArticleDOI
TL;DR: The abstraction of hydrogen and deuterium from ethane, 1,1-dichloroethane and 1, 1-trichloromethane by photochemically generated ground state chlorine atoms has been studied in this article.
Abstract: The abstraction of hydrogen and deuterium from ethane, 1,1-dichloroethane, 1,1,1-trichloroethane, and some of their deuterated analogs by photochemically generated ground state chlorine atoms has b...

Journal ArticleDOI
TL;DR: In this article, products of the reaction of OH radicals with 1-butene have been investigated in the presence of NO in one atmosphere of air at room temperature using gas chromatography and in situ long pathlength Fourier transform infrared absorption spectroscopy.
Abstract: Products of the reaction of OH radicals with 1-butene have been investigated in the presence of NO in one atmosphere of air at room temperature using gas chromatography and in situ long pathlength Fourier transform infrared absorption spectroscopy. The major product observed was propionaldehyde, with a formation yield (after allowing for its subsequent loss processes) of 0.94 ± 0.12. Minor yields of organic nitrates (RONO2) and of peroxypropionyl nitrate, a secondary product arising from propionaldehyde, were also observed. However, none of the products expected from the reactions subsequent to H-atom abstraction from 1-butene by OH radicals were observed, allowing an upper limit of 10% for this process to be derived. These data are compared with the available literature results and the implications are discussed.

Journal ArticleDOI
TL;DR: In this paper, a new reaction of triplet xanthone, hydrogen abstraction by a benzene ring, was found in the reactions with triethylgermane and sodium borohydride.


Journal ArticleDOI
TL;DR: Reduction de 3 cetones, cyclopropyl phenyl cetone, trifluoro-2, 2,2,2 acetophenone and fluoro-acetophenone par l'hydrure de triphenyl-sn. as mentioned in this paper.
Abstract: Reduction de 3 cetones, cyclopropyl phenyl cetone, trifluoro-2,2,2 acetophenone et fluoro-2 acetophenone par l'hydrure de triphenyl-Sn. Obtention de stannylethers. Effet du solvant sur la reactivite

Journal ArticleDOI
TL;DR: In this paper, the results of experiments involving in situ photochemical generation of the sulphate radical anion in the presence of some aliphatic carboxylic acids and their anions are interpreted in terms of attack at the car boxy group (to give alkyl radicals via decarboxylation) and hydrogen-atom abstraction from carbon atoms in the chain.
Abstract: The results of e.s.r experiments involving in situ photochemical generation of the sulphate radical anion in the presence of some aliphatic carboxylic acids and their anions are interpreted in terms of attack at the carboxy group (to give alkyl radicals via decarboxylation) and hydrogen-atom abstraction from carbon atoms in the chain. The general order of reactivity of different sites is CO2– > β-H, γ-H, etc. > CO2H > α-H. For example, reaction with EtCO2H gives ˙CH2CH2CO2H (k 2 × 105 dm3 mol–1 s–1) and Et˙(k 7 × 104 dm3 mol–1 s–1). Radicals formed by abstraction of α-H (e.g.˙CH2CO2H from ethanoic acid) are shown to result usually from further reactions of first-formed alkyl radicals. The reactions of SO4–˙ with some amides, nitriles, and esters have also been investigated.

Journal ArticleDOI
TL;DR: The photochemistry of three water soluble thioxanthone photoinitiators is studied in water using absorption, luminescence (fluorescence and phosphorescence) and conventional microsecond flash photolysis techniques.

Journal ArticleDOI
TL;DR: In this article, the experimental molecular mass decrease in the thermal depolymerization of poly-α-methylstyrene at 240°C in vacuum was simulated by Monte Carlo calculations, performed on the basis of certain hypotheses on the chemical evolution of the two chain radicals formed in a random scission reaction.

Journal ArticleDOI
TL;DR: The results prove that stereorandom hydrogen abstraction occurs in autoxidation and that the hydrogen loss bears no stereochemical relationship to chiral oxygen center(s) in the HPETE product, (8(R) or 8(S], or the 15(S)-hydroperoxy substrate.