Showing papers on "Radical ion published in 1988"
312 citations
TL;DR: The generalized free energy relationship for electron transfer (FERET) as mentioned in this paper is based on the conversion of the weak nucleophile-electrophile interactions extant in the ubiquitous electron donor-acceptor (EDA) precursor complex [D, A] to the radical ion pair [D⊕, A⊖], for which the free energy change can be evaluated from the charge-transfer absorption spectra according to Mulliken theory.
Abstract: The broad varieties of organic and organometallic reactions merge into a common unifying mechanism by considering all nucleophiles and electrophiles as electron donors (D) and electron acceptors (A), respectively. Comparison of outer-sphere and inner-sphere electron transfers with the aid of Marcus theory provides the thermochemical basis for the generalized free energy relationship for electron transfer (FERET) in Equation (37) and its corollaries in Equations (43) and (44) that have wide predictive applicability to electrophilic aromatic substitutions, olefin additions, organometallic cleavages, etc. The FERET is based on the conversion of the weak nucleophile–electrophile interactions extant in the ubiquitous electron donor—acceptor (EDA) precursor complex [D, A] to the radical ion pair [D⊕, A⊖], for which the free energy change can be evaluated from the charge-transfer absorption spectra according to Mulliken theory. FERET analysis thus indicates that the charge-transfer ion pairs [D⊕, A⊖] are energetically equivalent to the transition states for nucleophile/electrophile transformations. The behavior of such ion pairs can be directly observed immediately following the irradiation of the charge-transfer bands of various EDA complexes with a 25-ps laser pulse. Such studies confirm the radical ion pair [Arene⊕, NO2] as a viable intermediate in electrophilic aromatic nitration, as presented in the electron-transfer mechanism between arenes and the nitryl cation (NO) electrophile.
203 citations
TL;DR: The spin trapping electron spin resonance technique is used to provide for the first time direct evidence for sulfate anion radical formation during (bi)sulfite peroxidation.
132 citations
TL;DR: The similar pattern exhibited by ferric complexes on microsomal light emission and lipid peroxidation, and the same response of both processes to radical scavenging agents, suggests a close association between chemiluminescence and lipid each other, whereas both processes can be readily dissociated from free hydroxyl radical generation by microsomes.
84 citations
TL;DR: In this article, the same authors deduced key structural features of acceptor-doped polyaniline (polyemeraldine salt) from the crystal structures for the ClO 4 − and the BF 4 − dication salts of H(C 6 H 4 ǫ NH 6 H 6 H 5, radical cation salts of shorter oligomers and neutral H 5 C 6 C 6 NC 6H 4 NNH 6 H5, and showed that radical cations are
80 citations
66 citations
TL;DR: Using Electron Spin Resonance (ESR) spectroscopy, the cysteine thiol peroxyl radical is identified at low temperatures in two aqueous glasses and 17O isotopic substitution studies indicate dissolved molecular oxygen is the source of oxygen in CysSOO.
63 citations
TL;DR: Observations suggest that initial peroxidative attack occurs at the aromatic nitrogens of mitoxantrone, and the implications for suppression of lipid peroxidation in vivo are discussed.
59 citations
TL;DR: In this article, the light-induced radical cation of the primary electron donor P960+• in photosynthetic reaction centers from Rhodopseudomonas viridis has been investigated by ESR, ENDOR and TRIPLE techniques.
58 citations
TL;DR: In this article, time-resolved fluorescence detected magnetic resonance (FDMR) in pulse radiolysis of neat alkane liquids and binary alkane mixtures at room and low temperatures (approx. 180K).
Abstract: Alkane and olefin radical cations are characterized by time-resolved fluorescence detected magnetic resonance (FDMR) in pulse radiolysis of neat alkane liquids and binary alkane mixtures at room and low temperatures (approx. 180K). FDMR-EPR spectra of the cis-decalin radical cation and the norbornane radical cation are detected a low concentrations (10/sup -3/-10/sup -1/ M) of cis-decalin and norbornane, respectively, in alkane mixtures. Parent minus H/sub 2/ olefin radical cations are observed in neat alkanes and in alkane mixtures. Studies of the temperature and concentration dependences of olefin cation formation suggest that olefin cations originate in the fragmentation of parent alkane cations and that this reaction depends on the energy content of the parent cation. Other possible reactions of alkane radical cations are discussed.
58 citations
TL;DR: In this paper, the electrochemistry and spectroelectrochemistry of mononuclear, binuclear and tetranuclear zinc neopentoxy-substituted phthalocyanines are presented.
Abstract: The electrochemistry and spectroelectrochemistry of mononuclear, binuclear and tetranuclear zinc neopentoxy-substituted phthalocyanines are presented. The binuclear and tetranuclear species show two oxidation waves to the radical cation indicating the existence of stable mixed-valence, half-oxidized species. The electronic spectra of the half− and fully-oxidized species are presented and discussed. Nernstian analysis shows that pairs of phthalocyanine rings are oxidized simultaneously in the tetranuclear species, via a one-electron oxidation pathway.
TL;DR: The photochemistry of chloranil (Q) in the presence of the arenes hexamethylbenzene, 1-methyl-, 1-3-dimethyl-, 1,4-dimmethyl-, and 2,3dimethylnaphthalene, and acenaphthene has been investigated as discussed by the authors.
Abstract: The photochemistry of chloranil (Q) in the presence of the arenes hexamethylbenzene, 1-methyl-, 1,3-dimethyl-, 1,4-dimethyl-, and 2,3-dimethylnaphthalene, and acenaphthene has been investigated. Irradiation in a nonpolar solvent provided ether adducts resulting from formal addition of the quinone to the arene side chain, the hydroquinone, (QH/sub 2/), and in one case, an identifiable oxidation product, acenaphthylene. The quantum yield for these transformations was shown to have a complex dependence on the concentration of the arene and irradiation wavelength. On irradiation at 366 nm under conditions in which free chloranil absorbs, the preferred product was the reduced species, QH/sub 2/. On irradiation at 436 nm under conditions in which the ground-state charge-transfer (CT) complex of Q and the arene chiefly absorbs, the preferred product was the ether adduct. Excitation of complexes at 546 nm resulted in a sharply reduced quantum yield. Flash photolysis studies show that the quenching of Q triplets by the arenes leads to free radicals (QH/sup ./ and DH/sup ./) by a sequential electron-transfer, proton-transfer mechanism. Irradiation of QDH/sub 2/ complexes appears alternatively to lead to singlet radical ion pairs (Q/sup .-/, DH/sub 2//sup .+/) which evolve into singlet radical pairs (QH/sup ./, DH/sup ./) and final products inmore » competition with back reactions which return radical pairs to ground-state reactants.« less
TL;DR: In this article, the light-induced radical cation of the primary electron donor, P+.960, in photosynthetic reaction centers (RCs) from Rhodopseudomonas viridis has been investigated by various magnetic resonance techniques (ESR, ENDOR, TRIPLE).
Abstract: The light-induced radical cation of the primary electron donor, P+.960, in photosynthetic reaction centers (RCs) from Rhodopseudomonas viridis has been investigated by various magnetic resonance techniques (ESR, ENDOR, TRIPLE). Comparison of the measured hyperfine couplings with those of the cation radical of monomeric bacteriochlorophyll b (BChl b) and with RHF-INDO/SP molecular orbital calculations, performed on P+.960 using coordinates of an X-ray structure analysis, consistently show an asymmetric distribution of the unpaired electron over the two BChl b molecules which constitute P960. The derived spin density ratio is 2.8 in favor of the dimer half bound to the L protein subunit. The possible relevance of this result for the primary electron transfer step in the RC is briefly discussed.
TL;DR: In this paper, the role of pyridins in inhibiting the electropolymerisation of polycyclic pyrrole and N-methylpyrrole is examined.
TL;DR: In this paper, the authors performed triple resonance studies of 1,4-dihydro-1,3-diphenyl- (1a) and 3-tert-butyl-1.4-dimethyl substituted derivatives (2a and 2b) and showed that the spin density at N-4 is the position of highest spin density which determines the 1H and 14N hyperfine coupling (HFC) pattern.
Abstract: ESR, ENDOR and triple resonance studies of 1,4-dihydro-1,3-diphenyl- (1a) and 3-tert-butyl-1,4-dihydro-1-phenyl-1,2,4-benzotriazinyl (2a) and of the corresponding radical cation 3a (2a protonated at N-4) yielded the magnitude and the sign of almost all of the 1H and 14N hyperfine coupling (HFC) constants. Their assignment was performed using various 2H labelled and/or methyl substituted derivatives. Both radical groups show major hyperfine coupling to the three 14N nuclei. In the uncharged species 1a and 2a, the spin density at N-4 apparently directs the 1H HFC pattern in the 1,2,4-benzotriazinyl component, a(H-5) and a(H-7) being larger than a(H-6) and a(H-8). In the radical cation, on the other hand, N-1, with an unusually large splitting of 9.9 G, is the position of highest spin density which determines the 1H HFC pattern, a(H-6) and a(H-8) being larger than a(H-7).
TL;DR: In this paper, the results of the first systematic study of the effect of isotopic substitution on the rates of electron transfer for reactions in the inverted region were reported and the free energies of the electron-transfer reactions for both sets of ion pairs have been calculated, and in each case the reactions with deuterated cations was slower than with undeuterated radical cations.
Abstract: The results of the first systematic study of the effect of isotopic substitution on the rates of electron transfer for reactions in the inverted region are reported. Rates of return electron transfer within germinate radical ion pairs of 9,10-dicyanoanthracene (DCA) and 2,6,9,10-tetracyanoanthracene (TCA) radical ions and radical cations of perdeuteriated methyl-substituted benzene derivatives determined by a previously reported method are tabulated. The free energies of the electron-transfer reactions for both sets of ion pairs have been calculated, and in each case the reactions with deuterated cations was slower than with undeuterated radical cations. 1 fig., 2 tabs.
TL;DR: The evidence indicated that Radical 4 was the result of net hydrogen abstraction from N9 of the guanine base, and reaction mechanisms are proposed to account for formation of the products.
Abstract: SummarySingle crystals of guanine hydrochloride dihydrate, in which the guanine base is protonated at N7, were X-irradiated at 20K, 65K and 150K. Study with K-band ESR and ENDOR techniques indicated at least four radical species to appear in the temperature range 20–300K. Three of the radical species (Radicals 1, 2, and 3) were present immediately following irradiation at 20K. Radical 1 was identified as the molecular anion protonated at O6. Hyperfine couplings in Radical 1 to HC8, HN1, and HN7 were fully characterized with ENDOR spectroscopy. The data indicated this product to be trapped in four different conformations which coalesced into the most stable form as the sample temperature was raised to ca. 180K. Radical 2 was the C8 H-addition radical. For this radical, hyperfine couplings to HN7, HN9, and the two β-methylene protons were fully characterized with ENDOR spectroscopy. Radical 3 was the result of hydroxyl addition to C8 of the guanine base. For Radical 3, full characterization by ENDOR was pos...
TL;DR: In this article, the CIDEP spectrum of a geminate radical pair of the acetone-d6 ketyl radical in solution is reported, and it is shown that the radical pair spectrum of acetone d6 shows less M 1-dependent line broadenings than protonated acetone.
TL;DR: Ces energies sont discutees en liaison avec la conformation des deux chromophores carbazole as mentioned in this paper, avec the conformation of two chromophore carbazoles.
Abstract: Ces energies sont discutees en liaison avec la conformation des deux chromophores carbazole
TL;DR: In this paper, the authors report the title reaction, a comparable addition process whereby an alpha, omega-diene radical cation reacts by endocyclization and hydrogen shift(s).
Abstract: The classical example of a neutral carbon-centered radical cyclization reaction is the regioselective 1,5-ring closure (exocyclization) of the 5-hexenyl radical to the cyclopentylcarbinyl radical. Here the authors report the title reaction, a comparable addition process whereby an ..cap alpha.., omega-diene radical cation reacts by endocyclization and hydrogen shift(s) to produce a cycloolefin radical cation.
TL;DR: In this article, it was shown that the reaction with hydroxide ion is probably a S N 2 3 Ar * process and with piperidine involves a radical ion pair formed via electron transfer from the amine to a triplet excited state.
TL;DR: In this paper, it was shown that increasing the chain length between the halogen atoms, and increasing the electron release by the sulphur substituent, results in a red shift of the λmax. value and a decrease in radical cation yields.
Abstract: Intramolecular sulphur–iodine (S∴I–)+ and sulphur–bromine (S∴Br–)+ three-electron-bonded radical cations have been observed during the oxidation of various iodo-and bromo-alkylthioalkanes by ·OH radicals. For the bromo compounds, in addition, intermolecular (S∴S)+ radical cations are stabilized at high solute concentrations. Oxidation of alkylthio (chloro) alkanes leads only to the dimer sulphur-sulphur three-electron-bonded radical cations. All these radical cations exhibit optical absorptions in the visible and near u.v. with extinction coefficients in the order of 4 000–8 000 mol–1 dm3 cm–1. In general, increasing the chain length between the sulphur and the halogen atoms, and increasing the electron release by the sulphur substituent, results in a red shift of the λmax. value and a decrease in radical cation yields. In aqueous solutions most of the three-electron-bonded species decay by first-order kinetics with t1/2 up to 110 µs.
TL;DR: In this article, the authors studied the photoreduction of anthraquinone (AQ) by triethylamine (TEA) in toluene and ethanol by means of steady-state photolysis and laser photolysis.
Abstract: Photoreduction of anthraquinone (AQ) by triethylamine (TEA) in toluene and ethanol was studied by means of steady-state photolysis and laser photolysis. In toluene, addition of TEA enhanced the quantum yield of photoreduction of AQ, and the reaction was found to originate via the formation of an exciplex between ground-state TEA and the lowest triplet state of AQ: This exciplex changed to a contact ion pair followed by proton transfer, generating anthrasemiquinone radical and triethylamine radical, and 9,10-anthracenediol was obtained as the final photoproduct. Although the mechanism of the photoreduction of AQ in ethanol/TEA was essentially the same as that in toluene/TEA and the final products in ethanol/TEA were 9,10-anthracenediol and its anion, the quantum yield of photoreduction decreased with increase in TEA concentration. It was proposed that the exciplex in ethanol was quenched by ground-state TEA via the formation of a triplex of a radical anion of AQ and a radical cation of TEA dimer bonded by ...
TL;DR: The various mechanistic nuances of the catalytic mechanism have been considered and it has been shown that steady-state rotating-disc voltammetry alone can discriminate between almost all of the various pathways considered.
Abstract: The various mechanistic nuances of the catalytic (EC′) mechanism have been considered and it has been shown that steady-state rotating-disc voltammetry alone can discriminate between almost all of the various pathways considered. This deduction has been illustrated with reference to, first, the oxidation of the acetate anion in acetonitrile solution by means of the electrogenerated radical cation of tris(p-bromophenyl)amine and secondly, to the reduction of t-butyl bromide, in the same solvent, mediated through the radical anion of fluoranthene.