Fotochemische Primärprozesse von Xanthenfarbstoffen. VIII. Zum Einfluß von gemischten Mizellen auf die fotochemischen Primärprozesse von Selenopyronin und Erythrosin sowie die sensibilisierte Diazoniumsalzfotolyse

Photochemical Primary Processes of Xanthene Dyes. VIII. Influence of Mixed Micelles on the Photochemical Primary Processes of Selenopyronine and Erythrosine and the Sensitized Photolysis of Diazonium Salts The influence of the nonionic detergent dodecyltriglycol (DTG) on the escape rate of dye ions from cationic and anionic micelles is investigated. The rate constant of the escape of selenopyronine ions (Sp^⊕) from mixed micelles of sodium dodecylsulfate (NDS) and DTG (1:1) (k_A ≈︁ 3,2 · 10⁴ s⁻¹) is, as a result of the lower charge density, higher by the factor 10 than that from clean NDS-micelles (k_A ≈︁; 2,8 · 10³ s⁻¹). Erythrosine ions (Et^2⊖) are tightly fixed to cetyltrimethylammoniumbromide (CTAB)-micelles (k_A ≈︁; 0,25 · 10³ s⁻¹) and to mixed micelles of CTAB and DTG (1:1). This may be a result of the twofold negative charge of the erythrosine ions. Properties of the mixed micelles (polarity, average aggregation numbers) are determined by using the dyes and pyrene as probes. The sensitized photolysis of diazonium salts by electron transfer from photoexited selenopyronine under aerobic conditions is more effective by a factor of 3–5 in the presence of anionic micelles than when in a water solution.     

Kinetik und Mechanismus der Photolyse von Aryldiazoniumsalzen in Methanol. Ermittlung absoluter Geschwindigkeitskonstanten einiger Teilreaktionen

Kinetics and Mechanism of Aryldiazonium Salt Photolysis in Methanol. Determination of Absolute Rate Constants of Some Reaction Steps For benzene diazonium tetrafluoroborate and some p-substituted derivatives, the following values are determined:

• velocity constants for the photochemical electron transfer from pyrene and benzanthracene to aryl diazonium salts in acetonitrile solution (determination by quenching the donor fluorescence).
• velocity constants for electron transfer under the condition of pulse radiolysis in tert.-butanol-water solution;
• quantum yields and product composition (ArOMe, ArF and ArH, respectively) for the photolyses in methanol in the presence of varying concentrations of 2-methyl-2-nitroso-propane as a quencher of the thermal chain reaction.

The electron transfer reaction comes out be a diffusion controlled reaction, k_E = 2 …︁ 3 × 10¹⁰ M⁻¹ s⁻¹. For the total reaction a kinetic model is set up which affords absolute velocity constants from the experimental results for the following steps: Hydrogen transfer within the case radical pair \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {{\rm Ar} - {\rm N} = {\rm N}{\rm . CH}_{\rm 3} {\rm OH}{\rm .}} {\rm }^ \oplus $\end{document} (formation of ArH) k_H ≈ 10¹¹ s⁻¹; Maximal values for the photo-solvolyses (formation of Ar^⊕ → ArOMe and ArF, respectively), k_s ≲ 10⁻¹; Trapping of aryl radicals outside of the solvent cage by t-BuNO, k_q ≈ 2 × 10⁷ M⁻¹ s⁻¹. The results are discussed in the light of the kinetic model and some other facts.     

Reactions of Photoexcited Triplet States of Zinc Porphyrin with Transient Radicals in Aqueous Solutions

The technique of simultaneous pulse radiolysis and photolysis, PRAP, has been utilized to study the reactions of various radicals with ground state ZnTPPS and the triplet state ZnTPPS^T in aqueous solutions. The radicals H and OH add to both states with k ∼ 1 × 10¹⁰ M⁻¹ s⁻¹. The CH₂C(CH₃)₂OH radical from t-BuOH is relatively inert toward ZnTPPS but reacts rapidly (k = 1.8 × 10⁹ M⁻¹ s⁻¹) with ZnTPPS^T to form an adduct. Electron transfer reactions are found to be about an order of magnitude faster with the triplet than with the ground state. The (CH₃)₂COH radical reduces both ZnTPPS (k = 1 × 10⁸ M⁻¹ s⁻¹) and ZnTPPS^T (k = 3 × 10⁹ M⁻¹ s⁻¹) to the anion radical (ZnTPPS)⁻. The radical Br⁻₂ oxidizes both states to the cation radical (ZnTPPS)⁺ with k = 8 × 10⁸ M⁻¹ s⁻¹ for the ground state and 5 × 10⁹ M⁻¹ s⁻¹ for the triplet. The transient cation Cd⁺ reduces both states with a diffusion-controlled rate (k = 1 × 10¹⁰ M⁻¹ s⁻¹) to produce the anion radical. The above mechanisms of radical addition and electron transfer are also supported by the product spectra.     

Fotochemische Primärprozesse von Xanthenfarbstoffen. V. Untersuchungen zum Mizelleinfluß auf die fotochemischen Primärprozesse von Erythrosin

Photochemical Primary Processes of Xanthene Dyes. V. Investigations of the Influence of Micelles on the Photochemical Primary Processes of Erythrosine The triplet state of erythrosine decays in water solution mono- and bimolecularly (k₁ = 0,85 · 10⁴ s⁻¹; k_bi = 7,6 · 10⁸ l/mol s). As results of the bimolecular triplet decay a half-reduced and a half-oxidized form of the dye are observed. The dye ions are localized in the Stern layer of cationic micelles. The triplet state of those dye ions, which are localized individually at micelles, decays only monomolecularly (k = 2,1 · 10³ s⁻¹). If two or more dye ions are localized at a micelle, the bimolecular triplet decay takes place during the flash. Anionic micelles have no influence on the triplet decay processes of erythrosine.     

Photochemische Primärprozesse von Xanthenfarbstoffen. II. Blitzlichtspektroskopische Untersuchungen zum Einfluß von anionischen Mizellen auf die photochemischen Primärprozesse von Selenopyronin

Photochemical Primary Processes of Xanthene Dyes. II. Investigations of the Influence of Anionic Micelles on the Primary Processes of Selenopyronine by Flash Excitation In aqueous solutions containing anionic micelles, the dye cations of selenopyronine are present at the micellar surface. If the concentration of the dye ions is much lower than the concentration of micelles, only monomolecular triplet decay (k₁^aM = 2 · 10⁻³s⁻¹) is observed. Under these conditions, the half-oxidized and half-reduced form of selenopyronin is not formed. If the concentration of the dye ions is much higher than the concentration of micelles, two or more dye ions are present at every micelle, and a fast bimolecular decay of the triplet state during the flash is observed. The quenching of the triplet state with p-benzoquinone (k₇^aM = 1,9 · 10⁹ l/mol s), DABCO (k₁₀^aM = 1,6 · 10⁷ l/mol s) and EDTA (k₁₁^aM = 1,3 · 10⁵ l/mol s) and the decay processes of the half-reduced and half-oxidized form in the micellar solution are investigated.     

Flash photolysis investigation on primary processes of the sensitized polymerization of vinylmonomers. III. Photoreactions of benzoin compounds and stationary polymerization experiments

Benzoin (B), benzoinacetate (BA), benzoinmethylether (BME) and benzoinisopropylether (BIPE) were irradiated at room temperature in benzene solution in the presence of styrene (St), methyl methacrylate (MMA), vinylacetate (VAc) or acrylonitrile (AN). Flash photolysis experiments at λ=347 nm yielded (a) rate constants k_q (in 1 mol^-1s^-1) of the reaction between excited sensitizers and monomers: 8·10⁹ (B/St), 5·10⁸ (B/MMA), 5·10⁹ (BA/St), 8·10⁸ (BA/MMA); (b) rate constants K^R.+M (in 1mol^-1 s^-1) of the reaction between sensitizer radicals and monomers: about 1.5·10⁵ (BME/St, BME/VAc, BA/VAc, B/VAc), 9· 10⁴ (BME/MMA), 2·10⁴ (BME/AN). The reaction R·+M caused in certain cases (B/St, B/VAc, BME/St) the formation of an additional optical absorption after the flash. Stationary irradiations at λ>320 nm of monomer solutions (5mol/1) showed that BA is least effective. Rates of polymerization increased in the series BA<B<BIPE<BME. For the systems containing St or MMA it was found that ?_i=_i+0.6α_R (?_i=quantum yield for the initiation of kinetic chains, α_R =fraction of triplets converted to radicals). The fraction of radicals starting kinetic chains is ca. 0.3 in these cases.     

Reaction Kinetics of Hydroxyl Radicals with Model Compounds of Fuel Cell Polymer Membranes

The chemical stability of perfluorinated and non‐perfluorinated low temperature fuel cell model compounds (MCs) against attack by hydroxyl radicals, HO^•, is compared using a competition kinetics approach in aqueous solutions at ambient temperature. HO^• radicals were generated in situ by UV photolysis of hydrogen peroxide in the electron spin resonance (ESR) resonator. Acetic acid (AA), trifluoroacetic acid (TFAA), methanesulfonic acid (MSA), trifluorosulfonic acid (TFSA), and perfluoro(2‐ethoxyethane)sulfonic acid (PFEESA) were chosen as MCs, while the rate constants of 5,5‐dimethyl‐1‐pyrroline‐N‐oxide (DMPO) and methanol (CH₃OH) served as reference for the determination of relative rate constants by means of steady state ESR signal amplitudes. In decreasing order the rate constants are: k_MSA = (4.8 ± 0.2) × 10⁷ M^–1 s^–1, k_AA = (4.2 ± 0.3) × 10⁷ M^–1 s^–1, k_PFEESA = (3.7 ± 0.1) × 10⁶ M^–1 s^–1, k_TFAA = (7.9 ± 0.2) × 10⁵ M^–1 s^–1, and k_TFSA < 1.0 × 10⁵ M^–1 s^–1. Applying these results to perfluorinated fuel cell membranes like Nafion®, the main points of attack by HO^• are concluded to be the ether groups of the side chains, followed by the remaining carboxyl groups from the manufacturing process of the polymers.     

Zur Kinetik der photoinduziertenRadikalpolymerisation mit Elektronendonator/Elektronenakzeptor-Initiatorsystemen

Kinetics of Photoinduced Radical Polymerization with Electron Donor/Electron Acceptor Initiator Systems By means of benzyltriphenylphosphonium tetrafluoroborate (P^⊕) and anthracene (An) as photoinitiator system and methylmethacrylate (MMA) as monomer the influences of several reaction parameters on the polymerization quantum yield Φ_p, were studied. The following principal reactions proceed: electron transfer between excited An (¹An) and P^⊕ salt (k_q = 2,5 · 10⁹ M⁻¹ s⁻¹), quenching of ¹An by MMA (k = 1,3 · 10⁷ M⁻¹ s⁻¹), reaction between a ¹An…P^⊕ salt complex and MMA. The last reaction is assumed, since from the disappearance of An and the formation of An cation radical, respectively, rate constants k > 10⁸ M⁻¹ s⁻¹ have been calculated. Furthermore, it is assumed, that only the quenching of ¹An by MMA (Φ_p = 3,8) and the addition of free radicals, produced by the photoinduced electron transfer, lead to polymer formation. Kinetic equations were developed, which can explain the effect of P^⊕-salt concentration, light intensity and MMA concentration on Φ_p data. The quotient obtained for k_p/k is in the range of 0,053 to 0,087 M^−0,5 s^−0,5, depending on the used experimental parameters. Polymerization degrees P_n of 260–590 were found, which also depend on the experimental parameters.     

Pro- and Antioxidative Effect of α-Tocopherol on Edible Oils, Triglycerides and Fatty Acids

Using advanced electron paramagnetic resonance techniques (EPR), oxidation of crude vegetable oils and their components (fatty acids and triglycerides) by radicals generated from hydrogen peroxide was investigated. The correlation rotational times were determined allowing us to characterize radicals formed during edible oils oxidation. Additionally ¹H- and ¹⁴N-hyperfine coupling constants differentiate the fatty acids dependently on their unsaturation. The acids with a higher number of unsaturated bonds exhibit higher A_N values of PBN/·lipid adduct. The waste oil with high free fatty acids content underwent the oxidation reaction more efficiently, however due to saturation and the high content of the fatty acids the carbon-centered radicals formed (upon hydrogen peroxide radicals) and their PBN (N-tert-butyl-α-phenylnitrone) adducts were less stable. The antioxidant effect was dependent on the amount of α-tocopherol added. In small amounts of up to 0.35 mg/1 g of fatty acid or triglyceride, it inhibited the creation of PBN/·lipid adducts while with higher amounts it intensified adduct formation. The α-tocopherol (AT) addition influence was also studied as spin scavenging dependence and indicated that any addition of the antioxidant in the investigated samples led to free radical scavenging and the effect increased with the increase in AT content.     

Sensibilisierte Photolyse von Bis(dimethylglyoximato)cobalt(III)-Komplexen mit axial koordiniertem Azid bzw. Thiophenolat als photochemischen Opferliganden

Sensitized Photolysis of Bis(dimethylglyoximato)cobalt(III) Complexes with Axially Coordinated Azide or Thiophenolate as Photochemical Sacrificial Ligands The photolysis of [N₃Co(dmg)₂pyr] 1a and [PhSCo(dmg)₂pyr] 1b (dmg = dimethylglyoxime, pyr = pyridine) is sensitized by both [Ru(bpy)₃]Cl₂ 2 (bpy = 2,2′-bipyridine) and Michler's thioketone 3 (4,4′-bis(dimethyl-amino)-thiobenzophenone). Quenching of 2 by the cobalt(III) chelates 1a and 1b was studied by luminescence spectroscopy. The quenching rate constants calculated are in the order of magnitude of k_q ≅ 10⁶ mol⁻¹ s⁻¹. Polychromatic irradiation (> 250 nm) of 1b and 3 in the presence of thiophenole (PhSH) leads to hydrogen evolution, whereas long-wavelength (546 nm) irradiation does not. The results of these sensitization experiments support strongly a mechanism of catalyzed photolysis of PhSH as proposed earlier.     

Radiolytic Studies of the Cumyloxyl Radical in Aqueous Solutions

Formation and reactions of the cumyloxyl radical in aqueous solutions were studied by steady-state and pulse radiolytic techniques. Cumene hydroperoxide reacts with e⁻_aq (k = 4.4 × 10⁹ M⁻¹s⁻¹) to yield the cumyloxyl radical. The spectrum recorded after the pulse indicates formation of a species absorbing at 250 nm. This product was identified as acetophenone, which is formed by the fragmentation of the cumyloxyl radical. By comparison of the pseudo-first-order rates of e⁻_aq decay at 600 nm with the rate of production of acetophenone at 245 nm at increasing concentrations of cumene hydroperoxide, it was possible to derive a rate constant of 1.0 × 10⁷ s⁻¹ for the cleavage of cumyloxyl to acetophenone and methyl radical. This value is higher than that measured previously in organic solvents (1 × 10⁶ s⁻¹), as expected. HPLC analysis of the radiation products acetophenone and cumyl alcohol permitted determination of rate constants for hydrogen abstraction by the cumyloxyl radical, in competition with the fragmentation. The rate constants for H abstraction from i-PrOH, EtOH, and MeOH by CmO were found to be 9.9 × 10⁶, 3.8 × 10⁶, and 8.5 × 10⁵ M⁻¹ s⁻¹, respectively.     

Photochemie und Photophysik von 3-(2-Isoxazolinyl)-phenylketonen

Photochemistry and Photophysics of 3-(2-Isoxazolinyl)-phenylketones 3-Benzoyl-Δ²-1,2-oxazolines ( 1–6 ) are formed by 1,3-dipolar cycloaddition between benzoylnitril-N-oxide ( 8 ) and dihydrofurane 9 or 1,3-dioxep-5-enes ( 10a–c ). The preparative yields are small due to the competitive dimerization of the dipole 8 . Two stereoisomers are obtained by using 2-substituted 1,3-dioxep-5-enes as dipolarophiles. The different steric position of the substituents in 3–6 gives rise to different spectral data. The synthesized ketones possess triplet states with a high degree of charge transfer character. Therefore, the ability to H-abstraction reaction from alcohols is small. For ketone 2 and methanol as H-donor a rate constant of k = 4,1 · 10² M⁻¹s⁻¹ is determined. Also by electron transfer reactions with triethylamine and some onium compounds the reactivity of the T₁ of the ketones 1–6 is less compared to those of nπ* excited ketones. The photolysis of the ketones takes place very unselectively and leads to a product mixture. The quantum yields for the decay of the ketones are 10⁻² to 10⁻³.     

Photoinduzierte H-Abstraktionen an Benzylarylethern durch Benzophenon

Photoinduced H-Abstraction on Benzyl Aryl Ethers by Benzophenone The triplet state of benzophenone abstracts in benzene of benzyl aryl ether 6 hydrogen atom from the CH₂-group. The formed α-ether radicals 1 and diphenylhydroxymethyl radicals 8 react to form the three possible reaction products in statistical distribution. Benzaldehydes 2 and phenols 11 are formed in a side reaction. From quantum yield measurements of the benzophenone reduction in dependence upon the concentration of benzyl phenyl ether 6a follows a rate constant of the H-abstraction of 9.5 ·10⁵ M⁻¹s⁻¹ which is in good agreement with measurements in presence of naphthalene as a quencher. The quenching constant for benzophenone triplet by naphthalene is 2 · 10⁹ M⁻¹s⁻¹. For benzyl phenyl ethers substituted in the benzyl ring the reaction constant for the H-abstraction reaction was determined, ϱ = −0,68,     

Fragmentation of Fluorinated Model Compounds Exposed to Oxygen Radicals: Spin Trapping ESR Experiments and Implications for the Behaviour of Proton Exchange Membranes Used in Fuel Cells

Low‐molecular weight model compounds (MCs) for Nafion membranes used in fuel cells were exposed at 300 K to ^·OH radicals produced by UV irradiation of aqueous H₂O₂ solutions. The MCs contained fluorinated and partially fluorinated groups terminated by sulphonic or carboxylic acid groups. The fragmentation process in the MCs was studied by spin trapping electron spin resonance (ESR) methods, using 5,5‐dimethylpyrroline‐N‐oxide (DMPO), N‐tert‐butyl‐α‐phenylnitrone (PBN) and 2‐methyl‐2‐nitrosopropane (MNP) as the spin traps. The objective of these experiments was to assess the effect of the type of ionic groups (sulphonic or carboxylic) and of fluorine substitution on the spin adducts detected. DMPO experiments led to the detection of spin adducts of ^·OH and of carbon‐centred radicals (CCRs), and allowed the determination of the ^·OH attack site on the ionic and/or on the protiated or fluorinated groups. CCR adducts were also detected when using PBN as a spin trap; a key point in the interpretation of the PBN results was, however, the realisation that MNP is formed during PBN exposure to UV irradiation and oxygen or other oxidants such as H₂O₂. Experiments with MNP as the spin trap were the most informative in terms of structural details for adducts obtained from each MC. The results allowed the identification of CCRs present as adducts, based on large hyperfine splittings (hfs) from, and the number of, interacting ¹⁹F nuclei; in addition, oxygen‐centred radicals (OCRs) as MNP adducts were also identified, with much lower hfs from ¹⁹F nuclei. Taken together, the results deduced by spin trapping suggest that both sulphonic acid and acetic acid groups can be attacked by ^·OH radicals and confirm two possible degradation mechanisms in Nafion membranes: initiated at the backbone and at the side chain.     

Über die Verwendung von Nitrosomesitylen als Spin-Trap

On the Use of Nitrosomesitylene as a Spin Trap 2, 4, 6-Trimethylnitrosobenzene (nitrosomesitylene) has been tested for spin trapping of radicals. The rate constant for trapping of tert. butyl radicals by nitrosomesitylene has been estimated to be (1.2 ± 0.3) · 10⁸ mole⁻¹ dm³ s⁻¹.     

Reaction of dipyridamole with the hydroxyl radical

Dipyridamole [2,6-bis-diethanolamino-4,8-dipiperidinopyrimido-(5,4-d) pyrimidine], a well known platelet aggregation inhibitor, shows powerful hydroxyl radical scavenging activity by inhibiting OH-dependent salicylate and deoxyribose degradation. Steady-state competition kinetics experiments with deoxyribose were carried out to evaluate the second-order rateconstant for the reaction between hydroxyl radical and dipyridamole. OH· radicals were generated either by a Fenton-type reaction or by X-ray irradiation of water solutions. A second-order rate constant k_{(Dipyridamole+OH·)} of 1.72±0.11×10¹⁰M⁻¹ s⁻¹ and of 1.54±0.15×10¹⁰ M⁻¹ s⁻¹ was measured by Fenton chemistry and by radiation chemistry, respectively. Mannitol was used as an internal standard for hydroxyl radicals in steady-state competition experiments with deoxyribose. A rate constant k_{(Mannitol+OH·)} of 1.58±0.13×10⁹ M⁻¹ s⁻¹ and 1.88±0.14×10⁹ M⁻¹ s⁻¹ was measured in the Fenton model and in the water radiolysis system, respectively. Both these rate constants are in good agreement with the published data obtained by the “deoxyribose assay” and by pulse radiolysis.     

Kinetic study of the reaction between tocopheroxyl radical and unsaturated fatty acid esters in benzene

A kinetic study of the reaction between a tocopheroxyl radical and unsaturated fatty acid esters has been undertaken. The rates of allylic hydrogen abstraction from various unsaturated fatty acid esters (ethyl oleate2, ethyl linoleate3, ethyl linolenate4, and ethyl arachidonate5) by the tocopheroxyl radical (5,7-diisopropyltocopheroxyl6) in benzene have been determined spectrophotometrically. The second-order rate constants, k₃, obtained are 1.04×10⁻⁵ M⁻¹s⁻¹ for2, 1.82×10⁻² M⁻¹s⁻¹ for3, 3.84×10⁻² M⁻¹s⁻¹ for4, and 4.83×10⁻² M⁻¹s⁻¹ for5 at 25.0°C. Thus, the rate constants, k_abstr/H, given on an available hydrogen basis are k₃/4=2.60×10⁻⁶ M⁻¹s⁻¹ for2, k₃/2=9.10×10⁻³ M⁻¹s⁻¹ for3, k₃/4=9.60×10⁻³ M⁻¹s⁻¹ for4, and k₃/6=8.05×10⁻³ M⁻¹s⁻¹ for5. The k_abstr/H values obtained for the polyunsaturated fatty acid esters3,4, and5 containing H-atoms activated by two π-electron systems are similar to each other, and are about three orders of magnitude higher than that for the ethyl oleate2 containing H-atoms activated by a single π-system. From these results, it is suggested that the prooxidant effect of α-tocopherol in edible oils and fats may be induced by the above hydrogen abstraction reaction.     

Azomethinfarbstoffe - Sensibilisatoren,Löscher und Reaktionspartner für Singulettsauerstoff

Azomethine Dyes — Sensitizers, Quenchers and Reaction Partner for Singlet Oxygen Azomethine dyes show photofading in photographic materials, possibly due to oxidation by singlet oxygen. The azomethine dyes 1a–h , 2a–h , 3c , d , f are inefficient photosensitizers of singlet oxygen formation. In tetrachloromethane the quantum yield ϕ¹O₂ is in the range between 8 · 10⁻⁴ and 4 · 10⁻³. Contrary to the literature we found that azomethine dyes react with ¹O₂ (k_r). The reaction constants were measured by a competetive technique using 9, 10-diphenyl anthracene and methylene blue as ¹O₂ sensitizer. The values of k_r show that the reaction of the dyes with ¹O₂ can not be ignored. Besides this reaction, ¹O₂ is also quenched by the dyes (k_q). The values of k_q point to quenching of ¹O₂ by the tertiary amino group of the dyes via a CT-mechanism. This study shows that in photofading of azomethine dyes the oxydation by ¹O₂ must be taken into consideration.     

Selective study of paramagnetic centres in coals by e.s.r. and e.s.e. spectrometry

Electron spin resonance (e.s.r.) and electron spin echo (e.s.e.) studies of two natural and heat-treated bituminous coals are presented. In all samples, two main paramagnetic centres have been detected and studied selectively by obseving e.s.e. decays at different parts of the e.s.r. signal. These centres interact differently with neighbouring protons and the interaction is reduced in both centres by heat-treatment. The e.s.r. measurements reflect the heterogeneity of the region around the radical and are sensitive to the presence of proton hyperfine and dipolar broadening interactions. E.s.e. decays are sensitive to the presence of signals with longer spin memory time T_M. The T_M values obtained for all samples can be rationalized by assuming an exchange frequency in the range 1 × 10⁸ − 1 × 10⁹s⁻¹.     

Fourier Transform EPR Measurement of Homogeneous Electron Transfer Rates

Fourier-Transform Electron Paramagnetic Resonance has measured the rates of homogeneous electron transfer reactions involving duroquinone radical anions. The radicals are generated by laser photolysis of duroquinone in methanol solution containing 10% triethylamine. The duroquinone concentration was varied over a factor of 1000. The rate constant for electron transfer between the radical anion and the neutral duroquinone is 1.5×10⁸M⁻¹s⁻¹ and the intrinsic spin relaxation rates, T⁻¹₁ and T⁻¹₂ are 0.32 MHz and 0.44 MHz, respectively. Two-Dimensional magnetization transfer spectra show that the reaction is a homogeneous electron transfer reaction. The electron transfer rates are measured by two novel pulse sequences designed for more efficient data acquisition in samples with no unresolved inhomogeneous broadening. These two sequences result in a more rapid, accurate determination of the second-order chemical rate constant since the second-order rate constant is obtained directly and is not derived from a single measurement of a pseudo-first-order rate. The transient duroquinone radical anions studied here appear to have the same T₁, T₂ and electron transfer rates as stable duroquinone radical anions in alkaline solutions.