Showing papers on "Radical ion published in 1973"

Reactivity of the Hydroxyl Radical in Aqueous Solutions.

Abstract: : The reaction rate data of the hydroxyl radical in aqueous solution are compiled and evaluated in this critical review The values are reported in a series of tables covering addition, hydrogen abstraction, inorganic electron transfer and radical reactions Rate constants for the hydroxyl radical with biological molecules are included In addition, the rate constant data for the oxide radical ion are given Physical properties are listed and the experimental methods employed in OH radical chemistry are reviewed An analysis involving rate constant data comparisons is made

Production of Singlet Oxygen in Electrogenerated Radical Ion Electron Transfer Reactions

Abstract: The electrochemical reduction of oxygen generated superoxide ion and the electrochemical oxidation of ferrocene yielded the ferricenium ion. Both of these ion radicals were produced alternately in the same solution by pulsing the electrode potential between the reduction potential of oxygen and the oxidation potential of ferrocene. The homogeneous electron transfer reaction between superoxide ion and the ferricenium ion then produced ferrocene and singlet oxygen. The intermediacy of singlet oxygen was demonstrated by chemical quenching with 1,3-diphenylisobenzofuran (DPBF) which produced o-dibenzoylbenzene (DBB). The electron transfer reaction between superoxide and DPBF cation radical also produced singlet oxygen. he annihilation reaction between ion radicals has T recently been an area of intense study. It has been well documented that the mechanism of these reactions is an electron transfer reaction between a cation radical and an anion radical producing an electronically excited species and a neutral ground state molecule. 1--3 The effect of these reactions is the ultimate emission of radiation characteristic of the fluorescence of either RI or RS. When the ion radicals are generated electro(1) D. M. Hercules, Accounts Chem. Res., 2, 301 (1969); A. Wessberger and B. Rossiter, Ed., “Physical Methods of Organic Chemistry,” 4th ed, Part IIA, Academic Press, New York, N. Y., 1971. (2) A. J. Bard, I<. S . V. Santhanam, S. A. Cruser, and L. R. Faulkner, “Fluorescence,” G. G. Guilbault, Ed., Marcel Dekker, New York, N. Y., 1967, Chapter 14. (3) T. Kuwana, “Electroanalytical Chemistry,” Vol. 1, A. J. Bard, Ed., Marcel Dekker, New York, N. Y., 1966, Chapter 3. e (1) R1 + R1.C R1 + R2* + Rz + hv or IR? + RI* ----f Ri + hv (2) +e Rz R2*chemically, this phenomenon is called electrogenerated chemiluminescence (ecl). In ecl, both ion radicals are generated in the same solution by alternately pulsing the electrode potential from that where the reduction of Rl occurs to that for the oxidation of Rz. In this manner a very high concentration of ion radicals can be produced in a small volume near the electrode. Luminescence was not, however, the desired product in this investigation. Since electronically excited species are generated in ecl when the enthalpy of the Mayeda, Bard / Singlet Oxygen in Electrogenerated Transfer Reactions

Copper(I) carboxylates: preparations and infrared and mass spectral features

Abstract: Procedures for the high-yield preparations of a range of copper(I) carboxylates, CuO2CR (R = H, Me, CH2Cl, CHCl2, CF3, CH2CN, CH2SH, Et, Prn, Ph, o-NO2·C6H4, CHCHPh, and CHCH·CO2H) are reported. The i.r. spectra of these compounds are briefly discussed. The mass spectra of a selection of the copper(I) carboxylates show the presence of dimeric ions in high abundance in the vapour, together with very low abundances of trimeric and tetrameric ions. The alkanecarboxylates initially lose RCO2˙ from the radical ion Cu2(O2CR)2+˙, whereas the arenecarboxylates also easily lose CO2 from this radical ion leading to the formation of many ions containing Cu–C bonds. The monochloroacetate and o-nitrobenzoate also fragment to give ions possessing Cu–Cl and Cu–NO2 bonds respectively.

Crystal structure of the radical-cation radical-anion salt from 2,2′-bi-1,3-dithiole and 7,7,8,8-tetracyanoquinodimethane

Abstract: The three-dimensional structure of the radical-cation radical-anion salt from 2,2′-bi-1,3-dithiole (1) and 7,7,8,8-tetracyanoquinodimethane (2) has been determined by X-ray diffraction methods; the structure is composed of segregated columnar stacks of cations and anions.

Heterocyclic free radicals. Part IV. Some reactions of phenothiazine, two derived radicals, and phenothiazin-5-ium ion

Abstract: The reactions brought about when phenothiazine radical cation or phenothiazinium ion in acetonitrile is treated with aqueous solutions of various pH-values have been studied by spectroscopic methods. The proposed structure of a green dye which is formed under various conditions by the oxidation of phenothiazine has been confirmed. Evidence has been obtained about the modes of interconversion of phenothiazine and its oxidised derivatives.

Radical cations: photochemical and ferric ion-induced formation and reactions of indene radical cation

Abstract: Charge-transfer excitation of complexes of anhydrides with indene or 1,1-dimethylindene in polar solvents leads to cyclobutadimerization via radical cations; the same products are formed using pyrylium salts as photosensitizers, as well as from the thermal oxidation; with ferric chloride; these reactions are quenchable with efficient electron donors.

Intermediates in the pulse radiolysis of solutions of phenothiazine and its derivatives: reactions of cycloalkylperoxyl radicals with phenothiazines

Abstract: Aerated cycloalkane solutions of phenothiazine (PTH) undergo pulse radiolysis to yield a transient species (λmax 590 nm) building up after the pulse with k= 3·42 × 106 l mol–1 s–1(for C5H10). A comparsion of the spectrum with spectra of 3PTH, PTH·+, and PTH·–(or of its conjugate acid) prepared by unambiguois routes, and with literature spectra (where known) of these species, suggests that the transient is not any of these, but is more probably the neutral radical species PT·, formed by attack of cycloalkylperoxyl radicals upon the substrate. Further evidence for this is supplied by the presence of a primary deuterium kinetic isotope effect upon the rate of formation of the transient, and alternative preparations of the neutral radical are discussed. Pulse radiolysis of an aerated solution of N-methylphenothiazine (PTMe) in cyclohexane gives a different type of spectrum (λmax.ca. 520 nm) which is formed very rapidly even after 25 ns pulses and which is characterised by comparison with spectra of species generated by known routes as the radical cation PTMe·+, possibly formed by electron transfer between PTMe and RO2·. N-Benzyl-3,7-dioctylphenothiazine (dioctyl-PTCH2Ph) again reacts with RO2· on a ns time scale at mM solute concentrations; the species formed in this case has not been identified unambigiously, but may be dioctyl-PT· formed by the loss of the benzyl group.

Oxidation of some aromatic hydrocarbons by cerium(IV) trifluoroacetate

Abstract: The preparation of cerium(IV) trifluoroacetate, and its reactions with some benzenoid hydrocarbons in trifluoroacetic acid containing lithium trifluoroacetate, are described. With electron-rich compounds, oxidation is rapid at room temperature; the products are biaryls, diarylmethanes, and trifluoroacetate esters, the proportions of which depend on the structure of the aromatic compound. Evidence is presented that the first step is the transfer of one electron to the oxidant to form an aromatic radical cation; with methyl-substituted benzenes, this is followed either by reaction with another aromatic molecule or by deprotonation, subsequent reactions then yielding an ester or a diarylmethane.

Reactions of lead(IV). Part XXVIII. Oxidative coupling of methylsubstituted benzenoid compounds: formation of biaryls and diarylmethanes in trifluoroacetic acid

Abstract: Methyl-substituted benzenes are oxidised readily at low temperatures by lead tetra-acetate in the presence of trifluoroacetic acid; the products are mainly biaryls and diarylmethanes, in proportions which vary markedly with the structure of the aromatic compound. Evidence has been adduced that the first step is the formation of an aromatic radical cation. This undergoes competitive reactions; it can react with another aromatic molecule to give ultimately a biaryl, and in this respect behaves as an electrophilic radical rather than as a cation, or it can undergo further oxidation to give a benzylic cation from which diarylmethanes are derived.

Electron spin resonance studies. Part XXXVII. Oxidation of β-hydroxy-sulphides by the hydroxyl radical and structural features of sulphur-conjugated radicals

Abstract: E.s.r. spectroscopy in conjunction with a rapid-flow system has been used to show that both carbon radicals and thiyl radicals mediate in the oxidation of some β-hydroxy-sulphides with the hydroxyl radical in aqueous solution; the carbon radicals are detected directly and the thiyl radicals by way of their adducts with a spin trap. It is suggested that both types of radical are formed following the abstraction of an electron from sulphur; thus, the sulphur radical cation can undergo loss of a proton from an adjacent carbon atom or heterolysis of an adjacent C–C bond, to yield a carbon radical, or heterolysis of a C–S bond, to yield a thiyl radical. The structures of the carbon radicals are discussed in the light of the trends shown in their e.s.r. parameters.

Conformational isomerism in cation radicals of alkylthiophens

Abstract: Radical cations containing a thiophen ring substituted by 2,5-bisalkylthio-groups have been obtained and their e.s.r. spectra interpreted in terms of unequally populated rotational isomers. Assignment of their structure has been achived by examined the effect of steric hindrance caused by bulkyl substituents on the ratio of conformers. The hyperfine splitting constants have been assigned experimentally to the asymmetric conformers, the results being in agreement with the conclusions of theoretical methods. Theoretical calculations (CNDO/2) indicate that, for these derivatives, the most populated conformation of the radical cation corresponds to the most stable rotational isomer of the neutral molecule.

Diquaternary salts of 1,5- and 1,8-naphthyridines and the structure of their derived pseudo-bases

Abstract: 1,5-Naphthyridine and 1,8-naphthyridine react with dimethyl sulphate and with ethylene dibromide, respectively, to form 1,5-dimethyl-1,5-naphthyridinedi-ium dimethosulphate and 5,6-dihydroimidazo[1,2,3-ij][1,8]naphthyridinedi-ium dibromide. The salts readily form pseudo-bases. The salt from 1,5-naphthyridine is reduced by a one-electron transfer to give a relatively stable green radical cation.

On The Efficiency of Electrogenerated Chemiluminescence

Abstract: Electrogenerated chemiluminescence (ECL) occurs when redox reactions between oxidizing and reducing species generated electrochemically result in the production of light. Since the reactant species are frequently radical ions, this luminescence is sometimes called radical ion chemiluminescence, although a number of cases of ECL have now been described where at least one of the reacting partners is not a radical ion. Because a number of reviews (1-6) on ECL have appeared since the initial experiments described in 1964, only a brief outline of the methods and recent results will be presented here. A review of the experimental methods in ECL and an outline of the results of the as yet unreviewed research of 19701972 will appear shortly. (7)