Showing papers on "Radical ion published in 1972"
TL;DR: In this paper, the authors studied the reactions of the hydroxyl radical with a number of compounds containing the unit CHX-CHY, where X = OH or OMe and Y = OH, OAc, Halogen, or a protonated amino-group.
Abstract: The reactions of the hydroxyl radical with a number of compounds containing the unit –CHX–CHY–, where X = OH or OMe and Y = OH, OAc, Halogen, or a protonated amino-group, have been studied by e.s.r. spectroscopy. The transient species involved have been identified on the basis of their hyperfine splittings and g-factors; in the case of the radical ·CH(OH)·CH2NH3+ and its derivatives, clear trends in the proton and nitrogen nitrogen splittings are observed as the NH hydrogen atoms are successively replaced by methyl groups, and these have been rationalised in terms of an interaction involving both hydroxy- and amino-substituents.The data not only support the view that radicals containing the fragment –Ċ(OH)–C(OH)[graphic omitted] undergo acid-catalysed elimination of water but also reveal further details of this reaction and information about related heterolytic processes; for example, there is evidence that the radical cation MeOCH–ĊH2 is formed transiently from the radical ·CH(OMe)·CH2X (X = Cl or OAc). Amines do not appear to fragment heterolytically from radicals of the type ·CH(OH)·CH2NR3+, but the formation of the species Me3N·+ from the choline cation suggests that the C–N bond in the species ·CH(OH)·CH2NMe3+ readily undergoes homolysis.
71 citations
56 citations
55 citations
46 citations
TL;DR: In this paper, the primary reactions of hydrated electrons, hydrogen atoms and hydroxyl radicals with aniline and the cation in aqueous solutions have been studied by the technique of pulse radiolysis and by determination of end products after γ-radiolysis.
41 citations
32 citations
TL;DR: In this article, it was shown that tertiary aromatic amines can donate an electron to triplet benzophenone, and lend some credence to the previous postulate that amines react with triplet ketones by an electron-transfer process.
Abstract: Triphenylamine and tri-p-tolylamine quench the photoreduction of benzophenone by diphenylmethanol and in the case of triphenylamine, the quenching effect is substantially increased by a change of solvent from benzene to acetonitrile. Flash photolysis of nitrogen-flushed acetonitrile solutions of tri-p-tolylamine containing benzo-phenone, produced the amine radical cation and the radical anion of the ketone. When oxygenated solutions of either the amine alone of amine plus benzophenone were flash-photolysed, only the radical cation of the amine was observed. The lifetime and concentration of the radical cation is increased as the concentration either of oxygen or of benzophenone is increased. One of the modes of decay of the radical cation appears to be reaction with tri-p-tolylamine and a rate constant of 3·5 × 103 l mol–1 s–1 was determined for this process. Nitrogen-flushed acetonitrile solutions of triphenylamine gave, on flash photolysis, an intermediate (λmax. 610 nm) identified, from previous work, as cyclisation product, whereas when benzophenone is present in solution, the amine radical cation is produced. These results support the conclusion that tertiary aromatic amines can donate an electron to triplet benzophenone, and lend some credence to the previous postulate that amines react with triplet ketones by an electron-transfer process.
30 citations
29 citations
26 citations
TL;DR: In this article, a series of semiconducting organic radical-ion salts has been studied with regard to the potential use of such compounds in solid-state ion-selective electrodes.
25 citations
TL;DR: The authors showed that the unsolvated tetrameric aggregates of neophyllithium auto-xidize in major part by a path involving free neophyl radicals, while the solvated dimeric aggregates autoxidize predominantly by a route not involving free alkyl radicals.
Abstract: Neophyllithium (l) has been oxidized in solution by reaction with molecular oxygen at very low, controlled , rates. When autoxidation is carried out at 25\" in n-pentane or n-heptane solution, a significant fraction of the reaction products contain the benzyldimethylcarbinyl moiety; these products strongly implicate neophyl free radical as an intermediate. [n hydrocarbon solutions containing tetrahydrofuran or triethylamine, and in pure diethyl ether solution, formation oIthese products is largely suppressed. Neophyllithium is tetrameric in n-pentane at concentrations of 0.07 M but dimeric in diethyt ether at similar concentrations (-0. l0 M); vapor pressure studies establish that I coordinates strongly with tetrahydrofuran, but weakly with triethylamine and diethyl ether. Correlation of product distributions with the composition of the aggregates of I inferred from these physical studies indicates that the unsolvated tetrameric aggregates of neophyllithium auto,xidize in major part by a path involving free neophyl radicals, while the solvated dimeric aggregates autoxidize predominantly by a path not involving free alkyl radicals. Th. reaction of organolithium and-magnesium com-I pounds with molecular oxygen is important as a synthetically useful method of converting these reagents to alcohols and as an almost ubiquitous side reaction in their preparation and handling.,r-; These autoxida
TL;DR: In this paper, the decay of superoxide radicals in the presence of the enzyme was found to be first order in both enzyme and superoxide concentrations, with an apparent second order reaction rate constant of 2 × 109 M−1 sec−1, decreasing slightly as pH is increased from 5 to 9.5.
Abstract: The pulse radiolysis technique has been employed in the investigation of the dismutation of superoxide radicals, O−2 and HO2, in the presence of superoxide dismutase in aqueous solutions. The decay of superoxide radicals in the presence of the enzyme was found to be first order in both enzyme and superoxide concentrations. An apparent second order reaction rate constant was found to be about 2 × 109 M−1 sec−1, decreasing slightly as the pH is increased from 5 to 9.5. A mechanism which accounts for all our observations is proposed. It includes two steps: (1) formation of a product (EO−2 or E−) from one enzyme (E) molecule and one O−2 radical ion; (2) regeneration of E by a reaction of this product with an additional O−2 ion radical. The reaction rate constants k = (1.4 ± 0.2) × 109 and k = (1.9 ± 0.6) × 109 M−1 sec−1 were measured at pH = 7 in an oxygenated 0.16 M sodium formate solution.
TL;DR: In this article, a mechanism is proposed in which the fate of the radical cation determines the overall reaction product, and the mechanism is used to optimise the synthesis of anisaldehyde.
TL;DR: ESR spectrum due to 9,9′-biacriden radical cation (BAH2+·) was detected and its hfs was analysed and all the findings support the following equilibrium.
Abstract: ESR spectrum due to 9,9′-biacriden radical cation (BAH2+·) was detected and its hfs was analysed. BAH2+· exists in the degassed acidic ethanol solution of 9,9′-biacridyl (BA) and biacriden (BAH2) and is also produced by the photoreduction of BA in the acidic ethanol. All the findings support the following equilibrium. BAH++BAH2+H+ (Remark: Graphics omitted.) 2BAH2+·.
TL;DR: In this paper, the anodic oxidations of N-benzylidene-p-anisidines have been investigated by cyclic voltammetry and controlled potential electrolysis at a glassy-carbon electrode in acetonitrile.
Abstract: The anodic oxidations of several N-benzylidene-p-anisidines have been investigated by cyclic voltammetry and controlled potential electrolysis at a glassy-carbon electrode in acetonitrile. All the compounds tested were oxidized irreversibly. N-Benzylidene-p-anisidines showed two anodic waves. The relationship between the peak potentials of their first wave and the σ+ values of the substituents on the benzylidene group was linear, whereas that for the second wave was not. On controlled potential electrolysis at the first wave, protonated benzylidene-p-anisidines were identified, and on electrolysis at the potential of the second wave, p-benzoquinone imine and the corresponding benzaldehyde were identified as the main products. When water was added to the solution, the second wave shifted to a lower potential, whereas the potential of the first wave remained unchanged. Hence a combined wave was observed in the presence of sufficient water. On controlled potential electrolysis in the presence of 5% water, p-benzoquinone and the corresponding benzaldehyde were formed as the main products. Analysis of the minor product suggested that the p-anisidine radical cation was formed as an intermediate. A possible reaction mechanism is suggested.
TL;DR: In this paper, the spin density at the alkali nucleus in ion pairs with aromatic radical ions containing nitrogen was investigated experimentally and theoretically, and a quantitative theoretical description of the σ-π interaction was given.
Abstract: This paper deals with the spin density at the alkali nucleus in ion pairs with aromatic radical ions containing nitrogen. The mechanisms inducing the spin density have been investigated experimentally and theoretically. The E.S.R. spectra of 1,10-phenanthroline and 2,2'-dipyridyl reduced with sodium metal in dimethoxyethane have been measured in the temperature range -85 to +50°C. By comparing the alkali hyperfine splittings in the two compounds the importance of the polarization mechanism for the electron spin density at the counterion is estimated. In order to calculate the value of the spin density at the alkali nucleus as a result of the polarization mechanism only, a quantitative theoretical description of the σ-π interaction is given. A ‘McConnell-type’ relation between the π-density at the nitrogen centre and the sodium hyperfine splitting constant in a planar rigid σ-complex is derived. The proportionality constant is calculated as a function of the interionic distance in the complex. On the basis...
TL;DR: The e.p.r. spectrum of benzene on hydrogen mordenite (Zeolon H) has been studied as a function of coverage, degassing temperature, and hydrogen and oxygen treatment as discussed by the authors.
Abstract: The e.p.r. spectrum of benzene on hydrogen mordenite (Zeolon H) has been studied as a function of coverage, degassing temperature, and hydrogen and oxygen treatment. The initial spectrum observed was that due to the benzene cation radical dimer. The maximum number of spins was formed when the solid was completely saturated with benzene. Large yields were obtained only when the zeolitic water and water of hydration of the protons were removed. The largest yields were observed where significant dehydroxylation had occurred. Chemisorbed oxygen was essential, and there was a 1:1.2 ratio between the maximum number of spins observed in the presence of excess oxygen and the amount of oxygen chemisorbed. The largest concentration of radical cations noted (2 × 1018/g) was much smaller than the number of acid sites known to be present (1021/g). In fact, only one unit cell of the hydrogen mordenite in 100 had a site capable of oxidizing benzene to the cation. Hence these sites must be in special positions in the solid.
TL;DR: In this paper, the electron transfer in tetrahydrofuran (THF) or tetrahedropyrin (THP) solution by flash of light (λ > 420 nm) was studied.
Abstract: Photoejection of electrons from pyrenide ions (π. - ) or sodium pyrenide ion pairs (π. - , Na + ) was effected in tetrahydrofuran (THF) or tetrahydropyran (THP) solution by flash of light (λ > 420 nm). As the reaction was performed in the presence of a large excess of biphenyl (B) the ejected electrons were captured preferentially by that hydrocarbon reducing it to biphenylide radical ion (B. - or B. - , Na + ). Due to the low concentration of pyrene (π) the subsequent reactions between biphenylide and pyrene, namely B. - + π ( k 1 →) B + π. - (1) and B. - , Na + + π ( k 2 →) B + π. - , Na + , (2) could be easily monitored after the flash. By varying the ratio of [B. - ]/[B. - , Na + ] it was possible to make either (1) or (2) dominant, and hence to determine the rate constants k 1 and k 2 . Thus, k 1 = (4.8 ± 0.5) x 10 10 1 mol -1 s -1 and k 2 = 0.6 x 10 10 1 mol -1 s -1 for the electron transfer in THF, and k 2 = 0.5 x 10 10 1 mol -1 s -1 for the reaction in THP, all the constants referring to ≈ 20 °C.
TL;DR: Flash-photolysis experiments have shown that electronically excited fluorenone reacts with NN-dimethylaniline in polar solvents, to give the radical cation of the amine and the radical anion of the ketone.
Abstract: Flash-photolysis experiments have shown that electronically excited fluorenone reacts with NN-dimethylaniline in polar solvents, to give the radical cation of the amine and the radical anion of the ketone. In benzene solution, the only radicals detected were the 9-hydroxyfluorenyl radical and the fluorenone radical anion. By the same technique, excited fluorenone was shown to react with triethylamine in both polar and non-polar solvents to give the fluorenone radical anion and the 9-hydroxyfluorenyl radical. The former radical is probably produced by dissociation of the latter radical. The photoreactions of fluorenone with amines are interpreted in terms of exciplex and radical ion intermediates.
TL;DR: In this paper, the rate-controlling step in the e.c. process is base-assisted breakage of C−H bonds (reaction C 2 above), which accounts for the increased stability of the radical cation when compared to observation in aprotic solvents at room temperature.
TL;DR: In this article, a stable crystalline salt (e.g. perchlorate) of the methylphenazinium radical cation was obtained based on photoreduction of phenazine methosulfate in acid solution containing oxalate or tartrate.
Abstract: A stable crystalline salt (e.g. perchlorate) of the methylphenazinium radical cation was prepared. The method is based on the photoreduction of phenazine methosulfate in acid solution containing oxalate or tartrate.
TL;DR: In this article, a series of 1,4-diphosphoniacyclohexadiene salts has been reduced to a new class of radical cations for which e.g. data are presented.
Abstract: Electrochemical reduction of a series of 1,4-diphosphoniacyclohexadiene salts has produced a new class of radical cations for which e.s.r. data are presented.
TL;DR: In this paper, single crystals of cystine dihydrochloride were irradiated at room temperature with monochromatic uv radiation and two ESR centers were observed, the relative yield being approximately 1.
Abstract: Single crystals of cystine dihydrochloride were irradiated at room temperature with monochromatic uv radiation. The optical bandwidth was about 20 A for each wavelength used. Essentially two ESR centers were observed, the relative yield being approximately 1. One center is identified as the RS radical also detected after γ irradiation at room temperature, the second center is tentatively identified as a RS radical stabilized in an environment different from that of the first mentioned RS radical or alternatively as the RSS+R radical ion.
TL;DR: The isotropic g factors of some alkali metal-radical ion pairs have been measured, and significant g shift variations found, especially with heavy counter ions as mentioned in this paper, and a simple qualitative treatment of the effect adequately accounts for the experimental observation of positive and negative g shift upon ion pairing.
Abstract: The isotropic g factors of some alkali metal–radical ion pairs have been measured, and significant g shift variations found, especially with heavy counter ions.A simple qualitative treatment of the effect adequately accounts for the experimental observation of positive and negative g shift upon ion pairing.
TL;DR: In this article, a stable neutral free radical which is in equilibrium with its dimer at lower temperature was obtained by cathodic reduction of 3,5diaryl-1,2dithiolylium ions.
Abstract: Cathodic reduction of 3,5-diaryl-1,2-dithiolylium ions produces the corresponding stable neutral free radical which is in equilibrium with its dimer at lower temperature.
TL;DR: The radical cation formed by one-electron reduction of the 4,4′-bithiopyrylium dication has been characterized by its e.s.r. spectrum.
Abstract: The radical cation, formed by one-electron reduction of the 4,4′-bithiopyrylium dication, has been characterized by its e.s.r. spectrum.