Showing papers on "Radical ion published in 1971"
TL;DR: In this article, the indirect electrochemical reduction of triphosphopyridine nucleotide was investigated spectroelectrochemically using electrogenerated methyl viologen radical cation in the presence of the electron carrier, spinach ferredoxin-TPN-reductase.
114 citations
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42 citations
TL;DR: The chemiluminescence spectra resulting from the reaction of radical anions (A−) with Wurster's blue perchlorate (D+ClO4−) and exhibiting the monomer and excimer fluorescence of A have been investigated in this paper.
35 citations
35 citations
TL;DR: In this paper, a diazirinium radical cation was observed to lose a nitrogen atom to give a nitrilium ion whose substitution pattern was dependent upon the original substituents in the nucleus.
32 citations
TL;DR: In this paper, the quantum yield of the recombination reaction between tri-p -tolylaminium perchlorate and the radical anion of 9,10-dimethylanthracene in tetrahydrofuran at room temperature has been determined.
30 citations
28 citations
TL;DR: In this article, the anodic oxidation of aniline in an aqueous alkaline solution was studied, and the reaction mechanism was estimated through electrochemical measurements, chemical analysis, thin-layer chromatography, and UV, NMR, and IR spectrometries.
Abstract: The anodic oxidation of aniline in an aqueous alkaline solution was studied. The anode materials were Ni, C, Pt, and Pb. An organic deposit (film) was formed on the anodes. The reaction mechanism was estimated through electrochemical measurements, chemical analysis, thin-layer chromatography, and UV, NMR, and IR spectrometries. The de-electronation of lone-pair electrons of the N atom in an aniline molecule caused the radical cation to be produced, (Remark: Graphics omitted.), and this process was the rate-determining step. Some of the radical cations were found to couple together to produce azo-benzene via hydrazobenzene. The other radical cations led to p-amino diphenylamine by head-to-tail coupling; this product was de-electronated again to give the polymer with a quinoid structure.
28 citations
TL;DR: The pyridine radical anion shows an absorption maximum around 340 nm, the actual position varying with the counter-cation as discussed by the authors, due to formation of radical anions and dianions of 4,4′-, and 2,2′-bipyridyls.
Abstract: Pyridine radical anion, generated by alkali-metal reduction of pyridine shows an absorption maximum around 340 nm, the actual position varying with the counter-cation. The change in the spectra of the pyridine radical anion with time is due to formation of radical anions and dianions of 4,4′-, and 2,2′-bipyridyls. Alkylpyridines with substituents in the 3- or 4-position form stable radical anions which do not undergo dimerization. Electron-withdrawing groups produce a bathochromic shift of the absorption band of the pyridine radical anion.
26 citations
TL;DR: In this paper, it has been established that phenothiazine (PTH) undergoes photooxidation, PTH+O2 →PT·+HO2 in the aerated ethanol (dehydrated!) yielding a neutral radical as a stable product.
Abstract: It has been established that phenothiazine (PTH) undergoes photooxidation, PTH+O2\oversethν→PT·+HO2 in the aerated ethanol (dehydrated!) yielding a neutral radical as a stable product. The reaction is a one photon process and the reactive state is triplet PTH. It has further been established that the reaction occurs via a molecular complex (PTH-O2) most likely of C-T type, which has the absorption at ∼385 nm and decays with the first order rate constant of 1.6×102 sec−1. A similar transient C-T complex has been found to be produced from triplet PTH and dimethylisophthalate (weak electron acceptor) (absorption ∼385 nm, decay constant 2×103sec−1) with almost the diffusion controlled rate constant, although the eventual reaction does not occur. Thus in case of (PTH-O2), reaction (PTH-O2)→PT·+HO2 occurs while in case of (PTH-DMIP), the analogous reaction does not. Behavior of radical species (containing radical cation and (PTH-O2)) produced in the rigid aerated ethanol at 77°K has also been studied. The prese...
TL;DR: In this article, a linear relation of the polarographic anodic diffusion current to the UV absorbance was found, while the ESR signal intensity had linear relations with neither of the others in the system which contained an excessive number of parent molecules, 2×10−3M.
Abstract: The protonation mechanism of the aromatic hydrocarbon radical anions, such as biphenyl, naphthalene, phenanthrene, anthracene, 1,2-benzanthracene, and pyrene, in dimethylformamide (DMF) and water mixtures was studied. Three methods of measuring the concentration of the radical anions, i.e. polarography and ESR and UV absorption spectroscopy, were compared with each other by making simultaneous measurements of the same anthraquinone radical anion solution. A good linear relation of the polarographic anodic diffusion current to the UV absorbance was found, while the ESR signal intensity had linear relations with neither of the others in the system which contained an excessive number of parent molecules, 2×10−3M. The change in the visible absorption spectra of the aromatic hydrocarbon radical anions as a function of the time suggested that all the aromatic hydrocarbon radical anions decay by a first-order reaction. As a result, the radical anions were considered to decay through the following sequence:R\ewdo...
TL;DR: In this paper, the spin density at the metal nucleus in alkali radical ion pairs is derived by means of molecular orbital theory combined with first order perturbation theory, and the results show that the zero and first-order contributions to the metal spin density are of the same order of magnitude, but have different signs.
Abstract: Formulas for the spin density at the metal nucleus in alkali radical ion pairs are derived by means of molecular orbital theory combined with first order perturbation theory. The formulas have been used for computer calculations of the metal spin density in the Na naphthalene (NaNl) ion pair. The results show that the zero‐ and first‐order contributions to the metal spin density are of the same order of magnitude, but have different signs, and that the sign of the total spin density at the Na nucleus varies with the position of the Na ion in the ion pair. The experimentally observed dependence of the sign of the alkali coupling constant upon the atomic number of the metal is related to the difference in polarizing influence exerted by small and large ions on the π MO's of the aromatic ion. The temperature dependence of the metal coupling constant is explained by taking into account the change in the average position or the root‐mean‐square position of the alkali ion with a change in temperature.
TL;DR: In this paper, the splitting constants of the radicals formed by addition of the species S−· and ·SH to two olefinic compounds suggest that there is an interaction between the sulphur substituent and the tervalent carbon atom.
Abstract: Evidence has been adduced by e.s.r. spectroscopy for the formation of the sulphite radical anion, SO3–·[by the oxidation of sulphite ion with the hydroxyl or amino-radical, the sulphate radical anion, or cerium(IV) ion], of the thiosulphate radical anion, S2O3–·(from thiosulphate ion and the hydroxyl radical), and of the sulphide radical ion, S–·(pH 9) or the mercapto radical, ·SH (pH 2)(from sulphide ion and the hydroxyl or amino-radical). The radical anions are efficiently captured by nitroalkane aci-anions. The sulphite radical anion shows marked selectivity in its reactions with olefinic carbon. The splitting constants of the radicals formed by addition of the species S–· and ·SH to two olefinic compounds suggest that there is an interaction between the sulphur substituent and the tervalent carbon atom.
TL;DR: The electrochemical reduction of p -nitrophenyl thiocyanate in acetonitrle has been shown to be initially a one-electron process which gives the corresponding anion radical.
TL;DR: In this article, a remarkable difference has been found in the radical species produced when the alkali metal was changed from potassium to sodium in irradiated single crystals of acid salts of maleic acids.
Abstract: A remarkable difference has been found in the radical species produced when the alkali metal was changed from potassium to sodium in irradiated single crystals of acid salts of maleic acids. The room temperature stable species in an irradiated single crystal of potassium hydrogen maleate was previously found to be the symmetrical delocalized π radical formed by removal of the acidic proton. In contrast to this result, the stable species found in sodium hydrogen maleate was the radical formed by the addition of hydrogen to the double bond. Furthermore, it has been found that the addition takes place selectively to one of the two vinylene carbon atoms, as is unexpected from the symmetrical structure of the hydrogen maleate ion. A similar difference was also observed in the unstable species at 77°K. The potassium crystal gave the symmetrical σ radical formed by removal of the acidic proton while the sodium crystal gave the unsymmetrical σ radical. Here again the unpaired electron is selectively located in one of the two COO groups. These results indicate that the formation of radicals in crystalline solids is strongly affected by the surrounding crystalline field, since the sodium crystal is known to have a different crystal structure with hydrated water.
TL;DR: Two skeletal rearrangements of the type[ABC]-[AC]+. + B previously found in the mass spectra of 5-alkoxyisoxazoles are also seen for 5-amino- and 5alkylmercapto-isoxozoles as mentioned in this paper.
Abstract: Two skeletal rearrangements of the type[ABC]+.[AC]+. + B previously found in the mass spectra of 5-alkoxyisoxazoles are also seen for 5-amino- and 5-alkylmercapto-isoxazoles. They are discussed in terms of formation of an azirine ion and its ring expansion to an odd electron ion having a five-membered ring by means of bond formation involving nitrogen or sulphur. Fragmentation via an oxazole radical ion, which has a photochemical analogy, is also discussed.
TL;DR: In this paper, the hyperfine splitting constants obtained from the ESR spectrum indicated the removal of orbital degeneracy in the dimer radical cation by a cooperative intermolecular vibronic effect.
Abstract: The cobaltic trifluoroacetate oxidation of mesitylene in a rapid mixing flow system resulted in the formation of the mesitylene dimer radical cation. The hyperfine splitting constants obtained from the ESR spectrum indicated the removal of orbital degeneracy in the dimer radical cation by a cooperative intermolecular vibronic effect.
TL;DR: In this article, 1 : 1 complexes of closed-shell metal ions with the radical anion of glyoxal-bis-N-t-butylimine are reported.
Abstract: E.s.r. measurements of 1 : 1 complexes of closed-shell metal ions with the radical anion of glyoxal-bis-N-t-butylimine are reported.
TL;DR: In this article, the authors describe the oxidation of anthracene with cerium(IV) ammonium nitrate with a mesomeric ammonium radical and show that the resulting ammonium is attacked by a nucleophile to yield 10-methoxyanthrone or 10-acetoxynychrone.
Abstract: The oxidation of anthracene with cerium(IV) ammonium nitrate appears to occur through an initial anthracene radical cation which is transformed into a transient anthrol nitrate. Homolysis of the oxygen–nitrogen bond of the anthrol nitrate furnishes the nitrite radical and a mesomeric anthrone radical. While the former attacks the initial ion radical with a concerted mechanism to yield anthrol nitrite, the latter undergoes dimerisation to bianthrone, addition of a nitrate radical to yield 9,10-dihydro-10-oxo-9-anthryl nitrate which subsequently disproportionates to anthraquinone and nitrous acid, and oxidation to the anthrone cation. This is attacked by a nucleophile to yield 10-methoxyanthrone or 10-acetoxyanthrone according to the solvent used.
TL;DR: In this article, three kinds of radicals are observed following γ-irradiation of 1,3-butadiene adsorbed on silica gel, and the radical shows a change of the line profile with temperature.
TL;DR: The photo-oxidation of tertiary amines, but not of primary and secondary amines as mentioned in this paper, is interpreted as occurring via the formation of hydrocarbon radical anions and amine radical cations from the singlet states of the hydrocarbons.
Abstract: The photo-oxidation of tertiary amines, but not of primary and secondary amines, is sensitised by aromatic hydrocarbons (anthracene, naphthalene, perylene, and phenanthrene) in acetonitrile. Reaction does not occur in benzene. The reactions are interpreted as occurring via the formation of hydrocarbon radical anions and amine radical cations from the singlet states of the hydrocarbons. Amine radicals, which subsequently react with oxygen to give the products (imines, aldehydes, and secondary amines) may be formed by proton transfer from the amine radical cation to the hydrocarbon anion. Alternatively, proton transfer to the superoxide anion (O2–˙), formed by electron transfer from the hydrocarbon radical anion to oxygen, may occur. Quantum yields for the photoreduction of aromatic hydrocarbons by triethylamine and NN-dimethylaniline are reported.
TL;DR: The e.r.s. spectrum of 9,10-dihydrophenanthrene radical ion has been obtained in ether solvents at a number of temperatures between −106 and +51 °C as mentioned in this paper.
Abstract: The e.s.r. spectrum of 9,10-dihydrophenanthrene radical ion has been obtained in ether solvents at a number of temperatures between –106 and +51 °C. In dimethoxyethane–tetrahydrofuran mixtures below –80 °C, six triplet splittings are found with mean coupling constants of 5.36, 3.36, 2.66, 0.70, 0.26 and 0.15 oe. Above this temperature broadening occurs with some lines of the hyperfine spectrum due to motion resulting from the interconversion between the two equivalent conformers of the non-planar molecule ion. While the ring proton coupling constants are not strongly dependent on temperature, those due to the four methylene protons are, and interconversion between the conformers broadens the lines so that a 1:4:1 triplet is observed at low temperatures with a coupling of 2.97 oe. This is the sum of the axial and equatorial methylene proton splittings of a particular conformer. Near room temperature the motion is sufficiently rapid to give exchange narrowed lines and the process has an activation energy of...
TL;DR: In this paper, two classes of nonbenzoid compounds have been considered: (1) nonalternant hydrocarbons, and (2) bridged [10]and [14]-annulenes.
Abstract: Two classes of nonbenzoid compounds have been considered in this lecture: (1) nonalternant hydrocarbons, and (2) bridged [10]and [14]-annulenes. (1) The radical anion and cation of a nonalternant hydrocarbon should exhibit dissimilar e.s.r. spectra, in contrast to the two corresponding radical ions of an alternant system. This prediction of a simple MO model has been verified for four nonalternant compounds: acepleiadylene (I), acenaphth[ 1 ,2-a] acenaphthylene (II), acepleiadiene (III), and 3,5,8, 1 0-tetramethylcyclopenteno[ef]heptalene (IV). In all cases there is an excellent agreement between ex:periment and theory. (2) The degeneracies of both the lowest antibonding and the highest bonding perimeter orbitals are removed in a bridged [10]or [14]-annulene. The resulting energy sequence can be inferred from an MO perimeter model, if an adequate substituent effect is assumed for the bridging group. Since the e.s.r. spectra of the radical ions of bridged annulenes are determined by the energy sequence in question, they offer an experimental test of such an assumption. The substituent effect has been discussed for the bridging groups in 1,6methano[ lO]annulene (V), its iminoand oxido-analogues (VI and VII), syn-1,6: 8, 13-bisoxido[14] annulene (VIII), trans-15,16-dimethyl-15, 16-dihydropyrene (IX), and cyc1 [3,2,2] azine (X). INTRODUCTION Electron spin resonance (e.s.r.) spectroscppy is a powerful tool for testing the reliability of current n-electron models. With the exception of a few cases, only minor changes in the n-electron structure result, when an electron is added to or removed from an extended aromatic system. The radical ions can therefore be described by the same kind of n-electron models as the parent neutral compounds, and the information extracted from the e.s.r. spectra of the radical ions will in general also be characteristic of the neutral compounds1·2. Since the benzoid compounds are readily available, and their radical ions usually enjoy a remarkable stability, numerous studies of such radicals have been reported. In contrast, the number of radical ions derived from nonbenzoid aromatics is relatively modest1. A few examples will be presented in this lecture which attempts to give some insight into the potential of e.s.r. spectroscopy in the sturlies of interesting 7t-electron systems. * The topics dealt with in this lecture have been recently reviewed in ref. 1. 131
TL;DR: The u.v.visible spectra of 16 aromatic hydrocarbons have been measured in liquid antimony trichloride at 80 °C and they all show at least one clearly defined absorption band which is not observed in the absorption spectrum of either component alone as mentioned in this paper.
Abstract: The u.v.–visible spectra of 16 aromatic hydrocarbons have been measured in liquid antimony trichloride at 80 °C. They all show at least one clearly defined absorption band which is not observed in the absorption spectrum of either component alone. For the weakly basic polycyclic hydrocarbons the single band is attributed to charge-transfer interaction. The more basic hydrocarbons show additional bands due to R,SbCl2+ formed in the equilibrium reaction: R + 2SbCl3⇌ R,SbCl2++ SbCl4–. Perylene which is oxidised quantitatively to the radical cation in liquid antimony trichloride in the presence of oxygen shows an identical spectrum to that in sulphuric acid. The spectrum of naphthacene and pentacene radical cations has also been measured.