Showing papers on "Radical ion published in 1979"
TL;DR: In this paper, a mechanism for thermal production of excited states is discussed, where electron transfer from an easily oxidized donor to a suitable organic peroxide followed by oxygen-oxygen bond cleavage generates radical ion intermediates.
Abstract: : A mechanism for thermal production of excited states is discussed. Electron transfer from an easily oxidized donor to a suitable organic peroxide followed by oxygen-oxygen bond cleavage generates radical ion intermediates. Subsequent chemical reaction followed by charge annihilation generates electronically excitated state products. This sequence of reactions is called chemically initiated electron-exchange luminescence and is shown to be operating for diphenoyl peroxide, 1-phenylethylperoxy acetate, dimethyldioxeta-none, and 1,4-diphenyl-2,3-benzodioxin (0-xylylene peroxide). (Author)
339 citations
TL;DR: In this article, a photo-induced current was observed to indicate simultaneous production of CA− formed by electron transfer quenching of 3CA* by the medium, which is unambigously identified as product (besides CA−) of the electron transfer process.
Abstract: Excitation of p-Chloranil (CA) in propylcyanide (PrCN) at room temperature leads to rapid production of 3CA* which decays predominantly to CAH· with k = 1.6 · 105 s−1. Observation of a photoinduced current suggests simultaneous production of CA− formed by electron transfer quenching of 3CA* by the medium. Added naphthalene (NP) quenches 3CA* with kq = 7.0 · 109M−1S−1; NP+ is unambigously identified as product (besides CA−) of the electron transfer process. Dissociation of the ion pair occurs with essentially unit probability. Higher concentrations of NP lead to the formation of (NP)+2. Pertinent spectroscopic parameters established for NP+ under the conditions used are λmax = 685 nm (ϵ = 2970) using the known parameters of CA as reference. NP+ and CA decay by charge annihilation with kr = 4.5 · 109M−1S−1. The deviation from the diffusion controlled rate constant expected for ionic species, is discussed in view of the spin characteristics of the process. Comparison with two other ion recombination reactions leads to the conclusion that ‘inverted behaviour’ as expected from Marcus' theory does also not show up for backward e−-transfer between two ions (produced by forward e−-transfer between two neutrals). Residual absorptions in the system are ascribed to CAH·, tentatively proposed to originate from H+-abstraction by CA from the solvent. NP+ appears to be a rather stable species with respect to the medium if the latter is meticulously purified.
98 citations
TL;DR: In this article, the formation of radical cation complexes has been observed during the oxidation of cyclic and open-chain organic dithia compounds (the two S atoms not adjacent) by hydroxyl radicals in aqueous solutions, and a new sulfur-sulfur bond established by interaction of the unpaired p electron from the oxidized sulfur atom with the free p-electron pair of a second sulfur atom.
Abstract: The formation of intra- and some intermolecular radical cation complexes has been observed during the oxidation of cyclic and open-chain organic dithia compounds (the two S atoms not adjacent) by hydroxyl radicals in aqueous solutions. These species are characterized by a new sulfur-sulfur bond established by interaction of the unpaired p electron from the oxidized sulfur atom with the free p-electron pair of a second sulfur atom. Two of these electrons form a sigma bond while the third is promoted to an antibonding sigma/sup */ level. At low solute concentration (typically around 10/sup -4/M) intramolecular complex formation predominates. The radical cation complexes show characteristic broad optical absorptions which are attributable to a sigma ..-->.. sigma/sup */ transition. The position of the absorption maximum (reflecting the sigma/sigma/sup */ energy difference) and the extinction coefficients are related to the p-orbital overlap between the two interacting sulfur atoms. The extent of overlap depends on the internuclear distance, r(S therefore S), and particularly on the angular relationship between the interacting orbitals. Other structural parameters influencing lambda/sub max/ are the flexibility of the species formed and possible interactions between the sigma(S,S) bond with sigma(C,C) bonds. lambda/sub max/ is found to range from 400 to 650more » nm, these particular values referring to the intramolecular radical cation complexes from1,5-dithiacyclooctane and 1,4-dithiacyclohexane, respectively. epsilon values are found up to 7 x 10/sup 3/ M/sup -1/ cm/sup -1/. The lifetimes of the radical cation complexes depend on the stability of the new sulfur-sulfur bond and may well extend into the millisecond range in aqueous solutions.« less
76 citations
TL;DR: In this paper, the triplet-triplet absorption spectra of coumarin, 5.7 dimethoxycoumarin and 4'5′ dihydropsoralen with various pyrimidine and purine nucleic acid bases, and amino acids, have been determined by the techniques of pulse radiolysis and laser flash photolysis.
Abstract: —The triplet-triplet absorption spectra of coumarin, 5.7 dimethoxycoumarin and the furocoumarin 4'5′ dihydropsoralen. a model for 4'5′ psoralen-pyrimidine mono adducts, have been determined by the techniques of pulse radiolysis and laser flash photolysis. The extinction coefficients of the triplet transitions have been measured and used to determine the singlet triplet intersystem crossing quantum yields for 347 nm excitation in water. Reaction rate constants for coumarin and 4'5′ dihydropsoralen triplets with various pyrimidine and purine nucleic acid bases, and amino acids, have been measured. Long-lived transient absorptions detected after quenching coumarin and 4'5′ dihydropsoralen triplets with tryptophan are assigned to mixtures of the corresponding coumarin radical anion and the tryptophan radical cation. The spectra of the radical anions of coumarin and 4'5′ dihydropsoralen were established using pulse radiolysis of the coumarins in aqueous formate. It is suggested that coumarins and furocoumarin triplets are quenched by nucleic acid bases and amino acids via a chargetransfer mechanism.
52 citations
TL;DR: In this paper, the radical cation couple quadricyclane+ (Q+)/norbornadiene+ (NBD+) is considered and the barrier of interconversion is estimated to be significantly lower than that for the corresponding neutrals.
Abstract: The previously discussed principles involved in electrocyclic reactions of openshell ions are exemplified for a type C system, the radical cation couple quadricyclane+ (Q+)/norbornadiene+ (NBD+). Exhaustive calculations (MINDO/3) for the various states of the ions support the general predictions for such types of systems. The barrier of interconversion Q+ NBD+ is estimated to be significantly lower than that for the corresponding neutrals. Experimental support to this prediction is obtained by γ-irradiation of Q or NBD in an electron scavenging matrix. In both cases only NBD+ is observed, indicating that Q+ is not stable at 77 K. Previous observations and propositions referring to the system Q+/NBD+ are discussed in view of the present findings.
52 citations
TL;DR: The iron chelators, diethylenetriamine pentaacetic acid and deferoxamine, considerably reduced the amount of trapped hydroxyl free radical, suggesting iron was in part responsible for oxidation of 6-hydroxydopamine.
49 citations
32 citations
TL;DR: In this paper, the reaction of electron transfer from ascorbic acid to N-alkylphenothiazine radical cations was studied in the pH range 0 to 7.2.
Abstract: The reaction of electron transfer from ascorbic acid to N-alkylphenothiazine radical cations was studied in the pH range 0 to 7.2. The radical cations were produced by oxidation with Br/sub 2//sup -/ or Cl/sub 2//sup -/ using the pulse radiolysis technique. The radical cations are reduced by the deprotonated form of ascorbic acid in the pH range 2.2 to 7.2. The product of this reaction has a spectrum which is identical with that of the ascorbate radical. It is concluded that, if a charge-transfer complex is formed upon the reaction of ascorbic acid with the phenothiazine radical cations, its lifetime is shorter than 7 x 10/sup -8/s. It is suggested that even at high acidities no long lived complex is formed and it is proposed that at very low pH the thermodynamically stable species in this reaction is the phenothiazine radical cation rather than the ascorbic acid radical. It is shown experimentally that at 1 M HCl the ascorbic acid radical oxidizes N-alkylphenothiazine to give the radical cation of the latter in reverse to the direction of the electron transfer at higher pH. 8 figures, 2 tables.
32 citations
32 citations
TL;DR: In this article, the stability of both the radical anion and the radical cation of the same molecule can be rationalized by the unique combination of the twofold butatriene π-system with 4 R 3 Si substituents, which can act either as electron donors or electron acceptors and thus stabilize the ground state of either the cation or the anion.
30 citations
TL;DR: The first ionization potentials of 11 silylmethyl-substituted amines R 3−n N(CH 2 Si(CH 3 ) 3 ) n as determined photoelectron spectroscopy range from 9.07 eV to 7.66 eV as discussed by the authors.
TL;DR: In this article, the gas phase emission spectrum of the radical cation of all trans -1,3,5,7-octatetraene has been detected following excitation by a low-energy electron beam.
TL;DR: In this paper, the effect of added base on the electrochemical behavior of the conjugate base is described, and the effects of adding base on electrochemical behaviour are discussed.
TL;DR: The mechanism of the formation of the alkyl radical ions is quantitatively explained by using a method of calculation developed in an earlier publication for n-heptane as discussed by the authors.
Abstract: The fragmentation of n-hexane, n-nonane and n-tetradecane under electron impact has been investigated, using 13C labelled compounds. The mechanism of the formation of the alkyl radical ions is quantitatively explained by using a method of calculation developed in an earlier publication for n-heptane. It is assumed that these ions are formed either by a direct C-C bond cleaveage or by a secondary olefin loss from an alkyl radical ion. In the latter case the probability for a particular carbon to be lost in the neutral fragment is assumed to be random. The probability for a direct cleavage to an alkyl ion is about 80% for an ion containing at least half of the number of carbon atoms of the molecular ion and 15% for the smaller ions. The [MH]+ ion seems to be a special case not yet clearly understood. Former results about the loss of methyl from the molecular ion are confirmed.
TL;DR: In this article, the AlH+ radical cation has been trapped in a neon matrix at 4 K and studied via electron spin resonance spectroscopy (ESR) via rare gas matrix isolation ESR.
Abstract: The AlH+ radical cation has been trapped in a neon matrix at 4 K and studied via electron spin resonance spectroscopy (ESR). The magnetic parameters are Al: A∥=1009(3), A⊥=877(3) and H: A∥=A⊥=283(3) MHz; g∥=2.002(1) and g⊥=2.000(1). The isotropic and dipolar hyperfine components were calculated from ab initio CI and SCF type wave functions for comparison with experimental results. AlH+ is the first paramagnetic molecular cation studied via rare gas matrix isolation ESR spectroscopy.
TL;DR: In this article, the synthesis and properties of phenylene and biphenylbridged polymeric tetrathiafulvalenes are described, and the phenylene-bridged polymer-salts show a higher conductivity than the bi-phenylylene-branched ones up to values of 10−3Ω−1 cm−1.
Abstract: Tetrathiafulvalenes. VII. Arylene-bridged Polymeric Tetrathiafulvalenes
Synthesis and properties of phenylene — and biphenylbridged polymeric tetrathiafulvalenes, which are substituted by two methyl-groups in the 3- and 6-position, are described. These polymers react with bromine, iodine or tetracyanoquinodimethane to form the radical cation salts, whose electrical conducticity are estimated by means of powder compactions. The differences in the conductivity of the TCNQ-salts and radical cation halides are very small. The phenylene-bridged polymer-salts show a higher conductivity than the bi-phenylylene-bridged ones up to values of 10−3Ω−1 cm−1. Surprisingly the monomer salts have a lower conductivity than the polymer salts.
TL;DR: In this paper, the gas phase emission spectrum of dicyanodiacetylene radical cation has been detected, which lies in the 630-770nm wavelength region and was separated from the overlapping emission bands of the cyanogen radical by recording time resolved spectra.
Abstract: Gas phase emission spectrum of dicyanodiacetylene radical cation has been detected. The band system which lies in the 630–770 nm wavelength region was separated from the overlapping emission bands of the cyanogen radical by recording time resolved spectra. The He(Iα) photoelectron spectrum of dicyanodiacetylene is also presented and the inferred ionization energies, vibrational frequencies and assignments are given. From the latter data the emission spectrum is assigned as the ?2Πu→?2Πg electronic transition of dicyanodiacetylene radical cation. The frequencies of the four Σ+g vibrational fundamentals for the cationic ground state have been deduced from the emission spectrum.
TL;DR: In this article, it is shown that perylene is generated on the surface of a suitably prepared γ-alumina surface and a model involving cooperative interaction between the two types of redox sites, similar to that proposed by Pines for acid-base sites on this surface, is developed to explain the chemistry of aromatic hydrocarbons adsorbed on this form of alumina.
TL;DR: In this paper, a degassed tetrahydrofuran solution containing 10/sup -3/M each of 0-phenanthroquinone and UO/sub 2/(NO/sub 3/)/sub 2/6H/Sub 2/O was exposed briefly to light in the ESR cavity with 100-kHz modulation at -60/sup 0/C, a wellresolved spectrum was observed Prolonged UV radiation led to the disappearance of the spectrum and in its place a new spectrum was developed when irradiation was terminated.
Abstract: When a degassed tetrahydrofuran solution containing 10/sup -3/M each of 0-phenanthroquinone and UO/sub 2/(NO/sub 3/)/sub 2/6H/sub 2/O was exposed briefly to light in the ESR cavity with 100-kHz modulation at -60/sup 0/C, a well-resolved spectrum was observed Prolonged UV radiation led to the disappearance of the spectrum and in its place a new spectrum was developed when irradiation was terminated Both spectra are characterized by a low g factor and their ESR parameters are tabulated The analyses of the hyperfine structure are consistent with the assignments of (UO/sub 2/PQ)/sup +/ and (UO/sub 2/HPQ)/sup 2 +/, respectively, in which the unpaired spin is associated mainly with the phenanthroquinone moiety Chemically induced dynamic electron polarization results suggest that the formation of the unpolarized radical ion (UO/sub 2/HPQ)/sup 2 +/ is mainly a secondary photochemical reaction From the analysis of the transient response of the polarized (UO/sub 2/PQ)/sup +/ radical ion, an estimated T/sub 1/ of less than 08 mus is obtained Reaction mechanisms accounting for the formation of these radical ions are proposed 2 figures, 1 table
TL;DR: In this article, the ESR spectrum of the radical ion of the title compound was characterized spectroscopically and the reaction of Mn(CO)5− with [(CO)4CoGeCo3(CO)] was presented.
TL;DR: In this paper, the ESR spectra demonstrate that the extra electron is confined to the inner Si n C 2 n skeleton of the uncleaved and presumably planarized cyclopolysilanes.
TL;DR: In this article, the ion-host interaction potentials of the C6H6+ species in solid Ne and solid Ar are discussed in terms of the ion−host interaction.
Abstract: Matrix spectra of the C6H6+ species in solid Ne exhibit a well resolved vibrational structure, which shows a remarkably good agreement with the gas phase fluorescence. The ions in solid Ar are more strongly perturbed and show an interesting line shape asymmetry between the emission and excitation spectra. These are discussed in terms of the ion–host interaction potentials.
TL;DR: In this article, the oxidation of PH2 was studied spectroelectrochemically and the generated radical cation yields dimeric product which is subsequently oxidized in the same potential range.