Showing papers on "Radical ion published in 1977"
TL;DR: In this paper, a mechanism for the electrochemical oxidation of oxalate at a platinum electrode in acetonitrile solutions was proposed, which showed an irreversible two-electron oxidation at ca. 0.3 V vs. SCE to CO2 with no intermediates detectable by these techniques.
Abstract: The electrochemical oxidation of oxalate at a platinum electrode in acetonitrile solutions as studied by cyclic and rotating-ring disk voltammetry and controlled potential coulometry shows an irreversible two-electron oxidation at ca. 0.3 V vs. SCE to CO2 with no intermediates detectable by these techniques. The oxidation of oxalate in the presence of several fluorescers (such as rubrene, 9, IO-diphenylanthracene, and the bipyridyl chelates of ruthenium(l1) and osmium(l1)) does not produce light, but emission characteristic of the fluorescer occurs during the simultaneous oxidation of the additive and oxalate. Studies of the conditions for emission in the presence of thianthrene and naphthalene lead to a mechanism for the oxidation of oxalate and the excitation process based on oxidation of oxalate to CzO4-., which undergoes rapid decomposition to COz and C02--. The C02-e can transfer an electron to the additive molecule to produce a radical anion, which can then undergo an ecl annihilation reaction with the electrogenerated radical cation. There has been much interest in the intense chemiluminescence which results from the reaction of oxalyl chloride or oxalate esters and hydrogen peroxide in the presence of fluorescent compounds in nonaqueous solvents.’-3 In the proposed mechanism for these processes, the reaction between the oxalate ester and H202 produces the dioxetanedione (1) as an
185 citations
148 citations
09 Nov 1977
TL;DR: In this article, the lifetimes of the zeroth and some vibiationally excited levels of the B(π-1) states of the radical cations of hexafluorobenzene (1), pentafluorsenene (2), 1,2,3,4- (3), 1.2,4,5- (4) and 1.4,6,7-trifluorsensene (6) in the aaseous phase have been measured.
Abstract: The lifetimes of the zeroth and some vibiationally excited levels of the B(π-1) states of the radical cations of hexafluorobenzene (1), pentafluorobenzene (2), 1,2,3,4- (3), 1,2,3,5- (4) and 1,2,4,5-(5)-tetrafluorobenzene, 1,3,5- (6) and 1,2,4- (7)-trifluorobenzene in the aaseous phase have been measured. The cations were produced by 20—30 eV electron beam excitation of the samples at pressures < 10-3 torr The 00 level lifetimes (± 2 ns) found were 1 -48 us, 2 -47 ns, 3 - 50 ns, 4 - 50 ns, 5 - 30 ns, 6 - 58 os and 7 - 10 ns. The emission of 1,3-difluoralienzene radical cation (8) has also now been detected and the emission spectra of the fluorobenzenes 1-8,B → A, X band systems, are discussed. The emission intensities of the B →A, X transitions have been determined for 2-8 relative to 1. The lack of detectable emission from the corresponding excited (ir1) states of the radIcal cations of 1,4-and 1,2-difluorobeozene, fluorobeuzene, besizene and benzene-d6 indicates that the quantum yields of emission are < 10-5. The implications of the positive and negative results are considered with respect to the electronic structures of these species and the possible non-radiative pathways accessible to such excited cations.
81 citations
TL;DR: In this article, the photochemical reaction of 2-methyl-2-nitrosopropane (a spin-trapping agent) in benzene was studied at 299 K by monitoring the optical absorption intensity of the spin trapping agent and the ESR signal intensity of spin-adduct radical (di-t-butyl nitroxide).
Abstract: The photochemical reaction of 2-methyl-2-nitrosopropane (a spin-trapping agent) in benzene was studied at 299 K by monitoring the optical absorption intensity of the spin-trapping agent and the ESR signal intensity of the spin-adduct radical (di-t-butyl nitroxide). The observed kinetic feature was interpreted in terms of three elementary processes; the photodissociation of the spin-trapping agent giving a t-butyl radical, the spin trapping of the t-butyl radical by the trapping agent giving the spin adduct radical, and the reaction of the spin-adduct radical with the t-butyl radical giving diamagnetic products. The rate constant of the last process was found to be 10 times as large as that of the spin-trapping process, which was determined to be 3.3×106 mol−1 dm3 s−1 based on the reported rate constant for the scavenging of the t-butyl radical by tributylstannane. The relative spin-trapping rate constants toward the t-butyl radical were also determined to be 0.07, 1.0, 41, 63, and much higher than 50 for ...
52 citations
47 citations
TL;DR: In this paper, it was shown that normal polysulfides S x 2− with different chain length are the carriers of the yellow and red color, whereas the radical ion S 3 − is the blue species, which gives clear blue solutions or, if it is mixed with poly sulfide anions with × 6, green or carmine red, the existence of two further radical ions S 2 − (yellow) and S 4 − (red) in EPD-solvents.
Abstract: Alkali polysulfides dissolve in EPD-solvents (e.g. dimethylformamide, dimethylsulfoxide, and hexamethylphosphoramide) to give deep green, blue and carmine red solutions. Vis. and u.v. spectrophotometric as well as e.s.r. spectrometric investigations showed that normal polysulfides S x 2− with different chain length are the carriers of the yellow and red color, whereas the radical ion S 3 − is the blue species, which gives clear blue solutions or, if it is mixed with polysulfide anions with × 6, green or carmine red. U.v. and e.s.r. spectra point to the existence of two further radical ions S 2 − (yellow) and S 4 − (red) in EPD-solvents, The behaviour of polysulfides in these solvents can be understood by assuming that anions are only poorly solvated due to dipole shielding of the solvent molecules.
47 citations
TL;DR: In this paper, the formation of radical cations from the OH adducts of methylated benzenes in acidic aqueous solutions is demonstrated, where the radical cation is formed as an intermediate species in the water elimination reaction in which the adduct is transformed into the corresponding methylbenzyl radical.
Abstract: Formation of radical cations from the OH adducts of methylated benzenes in acidic aqueous solutions is demonstrated. The radical cation is formed as an intermediate species in the water elimination reaction in which the OH adduct is transformed into the corresponding methylbenzyl radical. The radical cations are also produced in neutral aqueous solution by reacting SO/sub 4//sup -/ radical ions with the methylated benzenes. The cations have two absorption bands, an UV band, 280-300 nm, and a visible band, 430-470 nm, with extinction coefficient of about 6500 and 2000 M/sup -1/ cm/sup -1/, respectively. The formation of the radical cations from the OH adducts depends on the hydrogen ion concentration, k/sub OH adduct+H/sup +// = (1.5 +- 0.5) x 10/sup 9/ M/sup -1/ s/sup -1/. The radical cations decay in acid solution exclusively into the corresponding methylbenzyl radicals.
46 citations
TL;DR: In this paper, the effects of solvent polarity on the photophysical properties of 1,10-phenanthroline indicate the close proximity of (n, π*) and (π, ε*) excited singlet states.
Abstract: The effects of solvent polarity on the photophysical properties of 1,10-phenanthroline indicate the close proximity of (n, π*) and (π, π*) excited singlet states, whilst the lowest triplet state is (π, π*) in all solvents. In hydrocarbon solvent, the first excited singlet state is of (n, π*) character but in water a (π, π*) is situated ∼ 700 cm–1 below this state. Even in water, the (n, π*) state is capable of abstracting a hydrogen atom from the solvent forming an intermediate semidiaza radical. The radical can be detected by flash photolysis and e.s.r. techniques and, in organic solvents, it decays with second order kinetics due to a disproportionation reaction. The major product of reaction is dihydrophenanthroline which, in hydrocarbon solvents, is formed with a quantum efficiency of ∼ 25 %. In aqueous solvent, the yield and rate of decay of the semidiaza radical are pH dependent, and the pK for protonation of the radical is 7.3. Thus, irradiation in water at pH 5 results in formation of the stable diprotonated radical cation.
42 citations
TL;DR: The nucleophilic photosubstitution at electron rich aromatic systems in solvents as water can therefore be classified as an S r + n 1(3Ar*) process as mentioned in this paper.
42 citations
TL;DR: In this paper, the e.s. spectra of methanol solutions of radical cations of the form (1; R = H, Me, Prn, Bun, or PhCH2), over a range of temperature from +40 to −90 °C, and determined the values of the splitting constants.
Abstract: We have studied the e.s.r. spectra of methanol solutions of radical cations of the form (1; R = H, Me, Prn, Bun, or PhCH2), over a range of temperature from +40 to –90 °C, and determined the values of the splitting constants. It is found that as the temperature decreases, the concentration of the radical cation decreases, until at –90 °C there is practically no e.s.r. spectrum. This process is reversible. Concentration experiments show that the radical cations are in equilibrium with a dimeric diamagnetic species. The thermodynamic constants for the dimerisation equilibrium were determined, and the results indicate that dimerisation involves desolvation, suggesting that in the dimer the radical cations are arranged in a plane to plane configuration, the two monomer molecules being linked together by a π–π′ bond. For (1; RCH3), i.e. for the radical cation of paraquat, reduction of the temperature is also accompanied by the production of a second paramagnetic species, the structure of which has not yet been determined.
39 citations
TL;DR: In this article, the radical cations and anions of a number of carbonyl containing polyenes of biological importance have been generated, and their absorptions characterised using pulse radiolysis techniques, and the wavelength maxima of the absorption bands are linearly dependent on the number of conjugated double bonds.
Abstract: The radical cations and anions of a number of carbonyl containing polyenes of biological importance have been generated, and their absorptions characterised using pulse radiolysis techniques. The wavelength maxima of the absorption bands are linearly dependent on the number of conjugated double bonds. The radical cation and the radical anion derived from the same parent molecule absorb at very similar wavelengths. There is a large hypsochromic shift in the radical anion absorption on changing from hexane to methanol solutions. The radical anions decay rapidly, in methanol, to form a species which is probably the protonated anion.
TL;DR: In this article, the authors report some highly specific ion-molecule reactions of various C6H6 radical cations produced by direct ionization of benzene and four of its acyclic isomers and by fragmentation of several more complex molecules.
Abstract: Various gas-phase C6H6 radical cations can be grouped in three general reaction categories depending on their origin. Ionized benzene reacts with 2-propyl iodide to displace an iodine atom and produce C9Hj3+. The rate constant for this reaction is 1.4 X IO-9 cm3 molecule-1 s-’ a t I I eV of ionizing energy. The major fraction of fragment C6H6 ions from styrene, cyclooctatetraene, anisole, benzaldehyde, phenylhydrazine, and chroman participate in the same reaction. A small proportion of the fragment [CsHs]+from benzaldehyde, chroman, and phenylhydrazine react with 2-propyl iodide by a second channel to give charge exchange. Ionic decarbonylation of tropone produces [C6H6]+’ which reacts with 2-propyl iodide exclusively by the charge exchange channel. These ions constitute a second category for gas-phase C6H6 ions. A third general class of [C&]+* is produced by direct ionization of various acyclic isomers of benzene (1,5-hexadiyne, 1,4-hexadiyne. 2,4-hexadiyne, and 1,3-hexadien-5-yne). The ions undergo charge exchange with 2-propyl iodide and give no detectable C9H 13+. Moreover, these acyclic ions react with their neutral counterparts to produce a rich array of gas-phase products and with I ,3-butadiene to give CsH,+, C9H9+, and [CloHlo]+.. This chemistry is not found with ionized benzene or the second category of [ChHs]+-. The differences in bimolecular chemistry are attributed to structural and energetic variations for the various C6Hh cations. This paper is a report of some highly specific ion-molecule reactions of various C6H6 radical cations produced by direct ionization of benzene and four of its acyclic isomers and by fragmentation of several more complex molecules. Because the structure and chemical properties of [C6H6]+have been of interest to many investigators, this study was undertaken to provide complementary information which would serve as a basis for reasonable deductions concerning the structure of this important gas-phase ion. Previous studies may be conveniently divided into two groups: (1) investigations of decomposing or “unstable” C6H6 ions, and (2) ion-molecule reactions and thermochemical measurements which reflect the stable, nonfragmenting C6H6 cations. The results for fragmenting ions have been employed either to determine the structure of ionized benzene or to understand the mode of carbon and hydrogen atom rearrangements which take place prior to fragmentation. Ever since the early study of Momigny et al.’ who reported the similarity in the mass spectra of benzene and various acyclic isomers (especially 1,3-hexadien-5-yne), it has been tempting to assume the intermediacy of an open chain isomer in the decompositions of [c6H6]+-. The similar kinetic energy released by [C&]+. formed in direct ionization of benzene and by acyclic2 [C6H6]+from charge exchange of [C6H6I2+ provides convincing support for this idea.3 Other C&+ions, generated by decomposition of more complex species, are nearly identical with ionized benzene, using the kinetic energy release criteriand presumably are also acyclic. Possible exceptions are the tropone-produced C6H6 ion, which releases twice the kinetic energy in the loss of a ~ e t y I e n e , ~ b and [C6H6]+from benzenechromium tricarbonyl, which yields distinctively different metastable intensities from ionized b e n ~ e n e . ~ However, there is a question whether C6H6 ions from benzene decompose from a single state or structure. The results of Andlauer and Ottinger,6 which have recently been confirmed by Smith and F ~ t r e l l , ~ and those of Jonsson and Lindholms have been interpreted in terms of isolated states, which give rise to noncompeting channels for loss of H and Hz vis-&-vis loss of CrHz and C3H3. Quasi-equilibrium theory (QET) calculations9 point to dissociation from the cyclic ground state ion to give C6H5+ and [C6H4]+whereas formation of [C4H4]+and C3H3+ involves either an electronically excited benzene ion or a ring-opened form. Recent photoelectron-photoion coincidence spectroscopy studiesI0 confirm the interpretations of Andlauer and Ottinger6 but may rule out the intervention of an electronically excited state. The early Q E T calculation of Vestal” shows that it is possible to account semiquantitatively for the fragmentation of ionized benzene by employing only the ground state of the molecular ion. Although the isolated states argument seems to be in contradiction with interpretations drawn from kinetic energy release measurement^^,^ and comparative mass spectrometry studies,’ both sets of data may be accommodated by a ratedetermining isomerization of [C&] +from benzene followed by rapid f r a g m e n t a t i ~ n . ~ ~ Moreover, the supporting Q E T calculations are not sufficiently sensitive to the choice of a cyclic ground state benzene ion rather than a ring-opened form. The other focus of studies of decomposing C6H6 ions has been the carbon and hydrogen scrambling which occurs prior to fragmentation.l2.l3 Contrary to the earlier suggestion that hydrogen scrambling proceeded via valence isomerization,I2 the more recent and thorough I3C and *H labeling shows independent C and H rearrangements.’* Although there are few experimental data to shed light on the mechanism of scrambling, we have reported a molecular orbital calculation which indicates that a single 1,2 exchange of hydrogen atoms on the intact ring can account for hydrogen atom r e ~ r g a n i z a t i o n . ’ ~ Like all simple aromatics, the molecular ion of benzene is stable, requiring between 4.79 and 5.01j eV of internal excitation before fragmenting. This means that electronic excitation, ring-opening, and carbon/hydrogen scrambling may preempt fragmentation. One purpose of this study is to determine if the existence of these processes can be verified by intercepting the “stable” ions in ion-molecule reactions. Before turning to a discussion of our results, a brief account of the available information on the stable ChH6 ions will be set forth. Thermochemical measurements show that the ground-state heat of formation of benzene is 233 kcal/mol16 which is too low for threshold formation of an acyclic Except for cubane and 1,3,5-hexatriene, other sources of [C6H6]+such as styrene, cyclooctatetraene, etc., give an excited benzene ion, not the acyclic form, a t the thresh01d.I~ These results do not agree with the conclusions drawn from perturbation molecular orbital theory that ionization of benzene yields an acyclic ion as the low-energy structure.18 A compilation of the thermochemical data is presented in Table I . High kinetic energy ion-molecule reactions also have been Gross et al. / Gas-Phase CsH6 Radical Cations
TL;DR: In this paper, a mechanistic scheme was proposed in which sensitizer and oxygen combine to produce sensitizers radical cation and superoxide radical anion, and the latter added to substrate to give a new radical which captures triplet oxygen.
Abstract: Singlet oxygen, generated chemically or photogenetically, reacts with biadamantylidene to give the corresponding dioxetane and epoxide only. When methylene blue (MB) or meso-tetraphenylporphin (m-TPP) is used as sensitizer the normal reaction course occurs giving dioxetane as the preponderant product in 2-propanol, ethyl acetate, acetone, pinacolone, methylene chloride, chloroform, carbon tetrachloride and benzene, although in the last two solvents some 10–25% of epoxide is formed. When erythrosin and rose bengal (RB) are used, epoxide becomes the main product (70–95%). Epoxide does not derive from chemical reaction with the solvent. Pinacolone, for example, is not oxidized to t-butyl acetate.
The rose bengal reaction involves both singlet oxygen and radicals, since diazabicyclooctane (DABCO) and di-t-butyl-p-cresol interfere with the oxidation. A mechanistic scheme is proposed in which sensitizer and oxygen combine to produce sensitizer radical cation and superoxide radical anion. Subsequently, hydroperoxy radical, deriving from superoxide, reacts with substrate to give epoxide and hydroxy radicals. The latter adds to substrate to give a new radical which captures triplet oxygen. Epoxide is formed by loss of hydroperoxy radical and the chain starts anew. The dioxetane is formed separately either by [2+2]-cycloaddition or stepwise addition.
TL;DR: In this paper, the reaction of OH radicals with mono-, di-and tri-methoxylated benzenes and benzoic acids has been further studied in aqueous solution.
Abstract: Using spectrophotometric and conductometric pulse radiolysis, in situ e.s.r. and product analysis techniques, the reaction of OH radicals with mono-, di- and tri-methoxylated benzenes and benzoic acids has been further studied in aqueous solution. It is found that, in addition to radical cations or zwitterions, phenoxyl radicals and methanol are formed. With the methoxylated benzenes the yield of phenoxyl radical is the same as the yield of methanol, and the sum of the yields of radical cation and of phenoxyl radical (or methanol) is ∼100% of G(OH). The ratio of the yield of radical cation to the yield of phenoxyl radical depends on the number and on the positions of the methoxyl groups relative to each other. The yields of phenoxyl radical are low when the methoxyl groups are meta to one another, whereas the yields are high for substrates with methoxyl groups in an ortho or para relation. A similar dependence on substrate structure of the distribution of products, i.e., radical zwitterions, phenoxyl radicals and methanol, is found for methoxylated benzoic acids.The results are quantitatively interpreted in terms of electrophilic addition of OH to the aromatic ring, the positions of attachment being governed by the ortho-para directing effect of the electron-donating methoxyl groups. H-abstraction from the methyl groups is negligible. The radical cations or zwitterions are derived from OH adducts formed by addition of OH to ring positions not occupied by methoxyl groups, whereas the phenoxyl radicals are produced by elimination of methanol (k∼ 4 × 104 s–1 at pH 7) from OH adducts formed by attachment of OH to ring carbons carrying methoxyl groups.
TL;DR: In this article, the evolution of the singlet character of correlated ion radical pairs, prepared by high energy impact (3 particles) in organic liquid and solid solutions, is monitored by nanosecond time resolved solute recombination fluorescence.
Abstract: The evolution of the singlet character of correlated ion radical pairs, prepared by high energy impact (3 particles) in organic liquid and solid solutions, is monitored by nanosecond time resolved solute recombination fluorescence. Results obtained show that the relative variations [IB(t) − I0(t)]/I0(t) of the luminescence intensity in presence IB(t) and in absence I0(t) of magnetic fields (B < 5 kG) decrease exponentially with time, according to a field and solute concentration dependent rate, in liquid but not in solid solutions; in the case of 2b PPD as solute, a damped oscillating component could be observed. The results are interpreted in terms of hyperfine interaction induced coherent singlet–triplet mixing and of field and solute concentration dependent spin–lattice relaxation.
TL;DR: In this article, the cationic ground and excited states of H 2 CSS have been assigned on the basis of ionization energies calculated from correlated PNO-CEPA wavefunctions.
TL;DR: In this paper, the existence of the OH adduct of DMA was demonstrated using nanosecond time resolution, and the adduct undergoes dissociation to hydroxide ions and radical cations with a rate constant of (7 +- 2) x 10/sup 6/ s/sup -1/.
Abstract: Pulse radiolysis of N,N-dimethylaniline (DMA) in neutral aqueous solution shows formation of N-methyl-anilinomethyl radicals and radical cations in a ratio of 1 : 2. The precursor for the two radicals is the OH radical. The existence of the OH adduct of DMA is demonstrated using nanosecond time resolution. This adduct undergoes dissociation to hydroxide ions and radical cations with a rate constant of (7 +- 2) x 10/sup 6/ s/sup -1/. The radical cation absorbs at 465 nm with an extinction coefficient epsilon/sub 465/ of 4500 M/sup -1/ s/sup -1/.
TL;DR: The spectrum of pulse-irradiated liquid 3-methyl octane at 127 K has maxima around 625 and 2100 nm as mentioned in this paper, which is very similar to bands observed earlier by Louwrier and Hamill in glassy solutions of higher hydrocarbons.
Abstract: The spectrum of pulse-irradiated liquid 3-methyloctane at 127 K has maxima around 625 and 2100 nm. The latter is well-known as being due to the solvated electron (es−). The former is attributed to a positive ion because it is eliminated by the addition of triethylamine, but remains in solutions of electron scavengers, and is very similar to bands observed earlier by Louwrier and Hamill in glassy solutions at 77 K of higher hydrocarbons in CCl4 or CO2-bubbled 3-methylpentane. At temperatures of 127 K and less the initial decay rate of es− is greatly decreased by the addition of ∼6mol% triethylamine. The result is interpreted as indicating that at low temperatures the mobility of the initial hydrocarbon positive ion is much greater than that of either es− or the positive ion in triethylamine solutions, and therefore the initial hydrocarbon positive ion must be the parent radical cation which moves by resonance charge transfer. As the temperature of pure 3-methyloctane is raised from 103 to 153 K, the initia...
TL;DR: In this paper, it was shown that in the homolytic hydroxylation of fluorobenzene and toulene a reversible acid-catalyzed dehydration will lead to an isomerization of the initially formed hydroxycyclohexadienyl radicals.
Abstract: The hydroxylation of fluorobenzene and toluene and the attempted hydroxylation of anisole, nitrobenzene, and benzonitrile by SO/sub 4/./sup -/ has been investigated. Fluorobenzene forms almost exclusively phenol and p-fluorophenol and toluene forms o- and p-cresol, bibenzyl, benzyl alcohol, and benzaldehyde. The proportions of these products depend on oxidizing metal salts and pH. The phenol isomer distribution is consistent with a nucleophilic attack by H/sub 2/O at the ..cap alpha.. and para positions of the radical cation. SCF-MO calculations (INDO) of the radical cations show the highest positive charge at the ..cap alpha.. and para positions. The results show that in the homolytic hydroxylation of fluorobenzene and toulene a reversible acid-catalyzed dehydration will lead to an isomerization of the initially formed hydroxycyclohexadienyl radicals. The absence of hydroxylation of nitrobenzene, benzonitrile, and anisole is probably due to the smaller positive charges at the ring carbons of the radical cations of these aromatics as compared to toluene and fluorobenzene radical cation.
TL;DR: The photoelectron spectrum of cyanogen fluoride (FCN) has been recorded, using He(I) and He(II) radiation as mentioned in this paper, and the spectrum can be unambiguously assigned through a correlation with the known photo-electron-spectroscopic data of the other cyanogen halides XCN, X = Cl, Br, I.
TL;DR: The first two vertical π-ionization energies of MX3 substituted benzenes as determined by photoelectron spectroscopy are compared with the results of modified CNDO/2 calculations, where M is Si or C and X is H, F, Cl and OCH3.
TL;DR: In this paper, a one-dimensional Hubbard model was applied to a solid ion radical salt and the transition energy and the theoretical line shape of the charge transfer absorption were derived and compared with those of certain TCNQ, anion radical salts.
Abstract: The electronic spectrum of solid ion radical salt is known to be different from the monomer spectrum of the radical ion and to show an intermolecular charge-transfer band in the low-energy region. In order to understand the character of this charge-transfer absorption, one-dimensional Hubbard model was applied to such solid ion radical salt. The transition energy and the theoretical line shape of the charge-transfer absorption were derived and were compared with those of certain TCNQ, anion radical salts.
TL;DR: In this paper, the redox properties of 2,3,7,8-tetramethoxyselenanthrene and 2, 3, 7, 8-tetracyanoquinodimethane were studied in solution in order to compare their potential applicability as charge-transfer donors.
Abstract: The redox properties of 2,3,7,8-tetramethoxyselenanthrene and 2,3,7,8-tetramethoxythianthrene have been studied in solution in order to compare their potential applicability as charge-transfer donors. The selenium compound is the weaker reductant, yielding a stable radical cation and a reactive dication, the former dimerizing in solution. Electron spin resonance and visible absorption spectra of the stable species were obtained. The 1:1 charge-transfer complexes of the above donors with tetracyanoquinodimethane are found to be insulators.
TL;DR: In this article, the hyperfine data for I2 · ⊕ are consistent with an effective D2h or D2d symmetry, the four benzene rings lying in parallel planes.
Abstract: Electrolytic oxidation of 4,5,7,8-tetramethyl[2.2]paracyclophane (I) yields a paramagnetic species which by ESR. spectroscopic evidence must be ascribed to the dimeric radical cation I2 · ⊕. Analogous dimers are obtained from the 12, 13, 15, 16-tetradeuterio- and 1, 1, 10, 10, 12, 13, 15, 16-octadeuterio-derivatives of I so that all coupling constants can be unequivocally assigned to sets of equivalent protons. The hyperfine data for I2 · ⊕ are consistent with an effective D2h or D2d symmetry, the four benzene rings lying in parallel planes.
TL;DR: In this article, the π-spin populations in the radical ions DPT and DPT· are to a large extent localized on the electron acceptor and donor moieties of the molecule, respectively.
TL;DR: In this paper, a mechanism for the electrochemical oxidation of oxalate at a platinum electrode in acetonitrile solutions was proposed, which showed an irreversible two-electron oxidation at ca. 0.3 V vs. SCE to CO2 with no intermediates detectable by these techniques.
Abstract: The electrochemical oxidation of oxalate at a platinum electrode in acetonitrile solutions as studied by cyclic and rotating-ring disk voltammetry and controlled potential coulometry shows an irreversible two-electron oxidation at ca. 0.3 V vs. SCE to CO2 with no intermediates detectable by these techniques. The oxidation of oxalate in the presence of several fluorescers (such as rubrene, 9, IO-diphenylanthracene, and the bipyridyl chelates of ruthenium(l1) and osmium(l1)) does not produce light, but emission characteristic of the fluorescer occurs during the simultaneous oxidation of the additive and oxalate. Studies of the conditions for emission in the presence of thianthrene and naphthalene lead to a mechanism for the oxidation of oxalate and the excitation process based on oxidation of oxalate to CzO4-., which undergoes rapid decomposition to COz and C02--. The C02-e can transfer an electron to the additive molecule to produce a radical anion, which can then undergo an ecl annihilation reaction with the electrogenerated radical cation. There has been much interest in the intense chemiluminescence which results from the reaction of oxalyl chloride or oxalate esters and hydrogen peroxide in the presence of fluorescent compounds in nonaqueous solvents.’-3 In the proposed mechanism for these processes, the reaction between the oxalate ester and H202 produces the dioxetanedione (1) as an