Showing papers on "Hydrogen atom abstraction published in 1971"
98 citations
93 citations
TL;DR: Coupled hydrogen bond systems have been shown to be interesting subjects of further research as discussed by the authors, for example, in ice, liquid water, hydroquinone clathrates, starch, cellulose, polypeptides, nucleic acids, and silicate hydrates.
Abstract: The “hydrogen bond” or “hydrogen bridge” concept has proved to be one of the most useful structural concepts in modern science. The properties of substances containing hydrogen bonds depend on the strength, symmetry, and polarity of these bonds. These characteristics, in turn, are related to the effective electronegativities of the bridgehead atoms, the distance between these atoms, and the degree of coupling with other hydrogen bonds. Symmetrical hydrogen bonds exist in the FHF− and H5O ions and in some acidic compounds. Coupled hydrogen bond systems exist, for example, in ice, liquid water, hydroquinone clathrates, starch, cellulose, polypeptides, nucleic acids, KH2PO4, and silicate hydrates. It is suggested that systems of coupled, nearly symmetrical, hydrogen bonds should be interesting subjects of further research.
92 citations
TL;DR: In this article, the reduction of a wide series of p- and m-substituted benzophenones and 2-substantituted fluorenones is studied in dimethylformamide.
91 citations
TL;DR: In this paper, a detailed kinetic analysis suggests that this order results from decreasing rates (in the given order) of self dimerization of the semipinacol radicals.
85 citations
TL;DR: In this paper, the rates of reaction of hydroxyl radicals with various aliphatic amines have been determined as a function of pH, including methyl, ethyl, isopropyl, t -butyl, trimethyl and triethyl amines.
59 citations
TL;DR: In this paper, a general procedure for the oxidation of olefin sulphides with perbenzoic acid to the corresponding episulphoxides has been established, based on the anisotropy effect of sulphinyl function and aromatic solvent induced shift.
54 citations
50 citations
TL;DR: In this paper, the reaction of CF3 radicals with benzene in the range 100-400°C was studied using the photolysis of hexafluoroacetone as a source of radicals.
Abstract: The reactions of CF3 radicals with benzene in the range 100–400°C were studied using the photolysis of hexafluoroacetone as a source of radicals. The addition of CF3 radicals to the benzene ring becomes reversible above ∼140°C. Below 140°C, pesudo H-abstraction occurs via the reactions CF3+ C6H6→CF3C6H6, CF3+ CF3C6H6→CF3H + C6H5CF3, but at higher temperatures, genuine H-abstraction by reaction (3) occurs CF3+ C6H6→CF3H + C6H5(3), and we obtain log k3(cm3 mol–1 s–1)=(11.31±0.28)–(9110±760)/θ, where θ= 2.303 RT cal mol–1. Combination of E3 and published data on E–3, (for the reverse of reaction (3)), gives ΔH°3 from which ΔH°f(C6H5)= 77.9±2.0, D(C6H5–H)= 110.2±2.0 kcal mol–1, both at 298 K. These values are compared with published data and the following are recommended: ΔH°f(C6H5)= 77.7±2.0 and D(C6H5—H)= 110.0±2.0, both in kcal mol–1.
50 citations
50 citations
TL;DR: In this article, the mechanism of oxygenation reactions catalyzed by a rhodium complex which forms a 1:1 molecular oxygen adduct has been elucidated by infrared spectroscopy.
Abstract: The mechanism of oxygenation reactions catalyzed by a rhodium complex which forms a 1:1 molecular oxygen adduct has been elucidated by infrared spectroscopy. Hydrogen abstraction from the substrate...
TL;DR: In this paper, the rates of the hydrogen abstraction reactions of fluorine atoms with hydrogen, four alkanes and methyl chloride were measured in the gas phase using a competitive technique, and new values of the activation energy for CH4 and C2H6 of 1850±230 and 480±20 cal mol-1 respectively were determined which are free from self-heating errors and are internally consistent when calculated from different competitive routes.
Abstract: The rates of the hydrogen abstraction reactions of fluorine atoms with hydrogen, four alkanes and methyl chloride were measured in the gas phase using a competitive technique. The compounds were arranged in the following series in which adjacent pairs were competed for fluorine: (i) H2, CH4, C2H6, H2(ii)CH3Cl, C2H6, C3H8, CH3Cl. New values of the activation energy for CH4 and C2H6 of 1850±230 and 480±20 cal mol–1 respectively have been determined which are free from self-heating errors and are internally consistent when calculated from different competitive routes. A value of 2470±270 cal mol–1 for H2 has been similarly obtained, which differs from previously reported values based on erroneous values for methane and ethane.
TL;DR: Single crystals of deoxyadenosine monohydrate grown from H2O and D2O solutions have been x irradiated and studied by electron spin resonance techniques at room temperature to show an isotropic coupling to one β proton and an anisotropic coupling of an α proton, consistent with a radical formed in the deoxyribose sugar group as a result of hydrogen abstraction at the C5′ position.
Abstract: Single crystals of deoxyadenosine monohydrate grown from H2O and D2O solutions have been x irradiated and studied by electron spin resonance techniques at room temperature. The results show an isotropic coupling of 7 ± 1.0 G to one β proton and an anisotropic coupling of an α proton with principal values − 22.6 ± 0.5 G, − 16.4 ± 0.5 G, and − 5 ± 0.5 G. The spin density on the carbon atom (C5′), calculated from the above results, is 0.64. The g‐tensor principal values are 2.0029 ± 0.0002, 2.0052 ± 0.0002, and 2.0075 ± 0.0002. These data are consistent with a radical formed in the deoxyribose sugar group as a result of hydrogen abstraction at the C5′ position.
TL;DR: In this article, the benzophenone-sensitised photo-oxidation of primary, secondary, and tertiary aliphatic amines and N-alkylanilines was investigated.
Abstract: Product studies are reported on the benzophenone-sensitised photo-oxidation of primary, secondary, and tertiary aliphatic amines and N-alkylanilines. Aliphatic amines gave aldehydes and imines, whereas N-alkylanilines were dealkylated but did not give imines. Amines which are known physical quenchers of singlet oxygen were efficiently oxidised. The reactivity of these compounds, and the type of products formed in the reaction, are explainable in terms of a mechanism in which hydrogen atom abstraction from the amine by triplet ketone is the primary chemical reaction. The results are not in accord with the participation of singlet oxygen. Quantum yield measurements of oxygen uptake, amine disappearance, and product formation are consistent with the proposed mechanism.
TL;DR: In this article, the spectral composition of light emitted when ions trapped during γ-irradiation are made to recombine has been studied in rigid matrices containing aromatic solutes: biphenyl, durene, styrene, naphthalene and pyrene.
TL;DR: In this paper, a number of quinones have been found to photosensitize the decarboxylation of acids of the type R1XCH2·CO2H (where X = O, S, and NH).
Abstract: Benzophenone and a number of quinones have been found to photosensitize the decarboxylation of acids of the type R1XCH2·CO2H (where X = O, S, and NH). The yields of substituted hydrocarbons (R1XCH3) formed by hydrogen abstraction by the alkyl radicals (R1XĊH2) and of addition products formed by reaction of the radicals with tetrachloro-p-benzoquinone as well as reduction products of the quinones have been determined. The yields of substituted hydrocarbons were often considerably increased by the inclusion of the good hydrogen donor, thiophenol, in the reaction mixture. The amino-acid studied, was found to give a substantial yield of the related aniline as well as the expected N-methylaniline. The benzophenone-sensitized reactions were retarded by oxygen whereas those sensitized by quinones were not. Addition of acetic acid was found to retard the reaction of phenoxyacetic acid with tetrachloro-p-benzoquinone.
TL;DR: The electron resonance spectra of a series of radicals derived by hydrogen abstraction from substrates containing carbon-carbon or carbon-nitrogen triple bonds have been studied in fluid solutions as mentioned in this paper.
Abstract: The electron resonance spectra of a series of radicals derived by hydrogen abstraction from substrates containing carbon-carbon or carbon-nitrogen triple bonds have been studied in fluid solutions The radicals ·CH2CN, ·CH2C ≡ CH and ·CH2C ≡ C·CH3 which have a linear heavy-atom framework show interesting temperature dependent line-width variations These are attributed to spin-rotational interactions arising from anisotropic molecular reorientation It is suggested that the motion about the long axis of these radicals is inertial in character The equilibrium geometries and hyperfine coupling constants of the propargyl and cyanomethyl radicals have been estimated from INDO-LCAO-SCF calculations
TL;DR: In this article, the infrared chemiluminescence arising from the hydrogen abstraction reactions of fluorine atoms with H2O, H2S, H 2O2 and CH4 was investigated at low pressure in a flow apparatus.
TL;DR: The gas phase photolysis of CCl4 in the presence of several alkanes has been used to obtain Arrhenius parameters for the abstraction of hydrogen atoms by the CCl3 radical.
Abstract: The gas phase photolysis of CCl4 in the presence of several alkanes has been used to obtain Arrhenius parameters for the abstraction of hydrogen atoms by the CCl3 radical:
The following log k4 values were obtained:
Text
Table Text. RH log k4
c-C5H10,
n-C6H14
2,3-Dimethylbutane
c-C7H14
Methylcyclohexane
c-C8H16
The results are compared to those for CH3 and CF3 radicals.
TL;DR: In this paper, the authors examined the absorption spectra of 1- and 2-piperidinoanthraquinones in a range of solvents of differing polarity and showed that their longest wavelength absorption band is intra-molecular charge transfer (c.t.) in type.
Abstract: An examination of the absorption spectra of the 1- and 2-piperidinoanthraquinones in a range of solvents of differing polarity shows that, in their unprotonated forms, their longest wavelength absorption band is intra-molecular charge-transfer (c.t.) in type. On protonation of the 1-piperidino derivative the longest wavelength band becomes n$\pi ^{\ast}$ and this is accompanied by a marked difference in photochemical behaviour. Photoreduction of the unprotonated 1-piperidino derivative in alkaline solution occurs by the conventional reactions of hydrogen abstraction, followed by combination of two semiquinone radical anions to form the corresponding dianion. With 2-piperidinoanthraquinone, the final reduction product is the semiquinone radical anion formed by an electron transfer process from hydroxide and alkoxide ions to the photo-excited c.t. state of the quinone. The relevance of these observations to the mechanism of phototendering of cellulose materials by vat dyes is discussed.
TL;DR: Several NN-diethyl-1-naphthyl-alkylamines (NN-1, NN1, and NN9) exhibit intramolecular exciplex formation and as a result reactions typical of the hydrocarbon singlet states, e.g., hydrogen abstraction from tertiary amines and dimerisation, are quenched.
Abstract: Several NN-diethyl-1-naphthylalkylamines and NN-diethyl-9-anthrylalkylamines exhibit intramolecular exciplex formation and as a result reactions typical of the hydrocarbon singlet states, e.g. hydrogen abstraction from tertiary amines and dimerisation, are quenched.
TL;DR: In this article, the relative rate constants for Si-H hydrogen abstraction from substituted phenylsilanes, phenylmethylsilanes and phenyldimethylsilanes by the trichloromethyl radical have been determined from competitive chlorinations at 80° with carbon tetrachloride as the chlorinating agent.
TL;DR: In this paper, the authors studied the rate of radical formation in photosensitized dehydrogenation of durene doped with 2,4,5,trimethylbenzaldehyde and naphthalene-d8 gives rise to duryl radicals.
Abstract: The photosensitized dehydrogenation of durene doped with 2,4,5‐trimethylbenzaldehyde and naphthalene‐d8 gives rise to duryl (2,4,5‐trimethylbenzyl) radicals. The rate of production of these radicals was studied as a function of the guest, of photolyzing light intensity, and of temperature. The experimental data show that the mechanism of radical formation is dependent upon the nature of the particular guest involved. In naphthalene‐d8/durene mixed crystals, duryl radical is probably formed by a stepwise biphotonic absorption process involving the first triplet state of the guest as an intermediate. The results show that radical formation is not responsible for the temperature dependence of the naphthalene‐d8 phosphorescence lifetime in durene host at T > 220°K. In 2,4,5‐trimethylbenzaldehyde/durene mixtures, the formation of duryl radical is a monophotonic process, and the over‐all reaction is the hydrogen abstraction of aromatic carbonyl compounds with a lowest nπ* triplet state, a process which has been...
TL;DR: The photochemical addition reaction of 3-cyano, 3-chloro-, 3-methoxy-cyclohexanone, and some 3-aminocyclohexenones have been investigated in this article.