Showing papers on "Radical ion published in 1970"

Bis-1,3-dithiolium chloride: an unusually stable organic radical cation

Abstract: Treatment of bis-1,3-dithiole with 1 equiv. of chlorine affords a very stable radical cation which is amenable to full chemical and spectroscopic characterization.

Gas-phase reactions of oxide radical ion and hydroxide ion with simple olefins and of carbanions with oxygen

Abstract: Reaction channels, branching ratios, and rate constants have been measured and reaction probabilities have been calculated for the reactions of oxide radical ion and hydroxide ion with simple olefins and for the reactions of carbanions with molecular oxygen. All investigations were carried out in a flowing afterglow system in the gas phase at 22.5' under conditions of thermal equilibrium. Oxide radical ion reacts rapidly and efficiently with allene, propene, 2-methylpropene, 1-butene, and cisand trans-2-butene to abstract either a hydrogen atom to yield hydroxide ion or a proton to yield a carbanion. Rate constants are of the order of 7 X 10\" M-l sec-l and reaction probabilities range from 0.42 to 0.84. The reaction of oxide radical ion with ethylene is believed to proceed cia associative detachment. Hydroxide ion reacts efficiently with the simple olefins except ethylene only by proton abstraction to yield the conjugate base of the carbon acid. Rate constants and reaction probabilities range from 1.6 to 5.3 x 10\" M-1 sec-1 and 0.11 to 0.46, respectively. The following gas-phase acidity order has been observed : simple olefins > water > ethylene, saturated hydrocarbons. The carbanions C3H3-, C3H5-, and C W 7 react with molecular oxygen cia a variety of channels including electron transfer, hydride transfer, and rearrangement. The observed reaction kinetics has been used to estimate limits for the standard heats of formation of C2H3-, C3H3-, C3H5-, and C4H,and limits for the electron affinities of the corresponding free radicals. ecent gas-phase investigations of negative-ion orR ganic chemistry have illustrated the difficulties inherent in the determinat ion of the intrinsic kinetics a n d thermodynamics of organic reactions f rom solution measurements. For example, detailed examinations of Brgnsted acid-base reactions by ion cyclotron resonance spectroscopy3 a n d in t andem mass spectrome t e r ~ ~ have established tha t intrinsic acidities can differ markedly f rom solution acidities in which such perturbat ions as hydrogen bonding, specific solvation, a n d aggregation can have overriding influences. It is the purpose of this paper t o describe a generally useful technique for the study of thermal energy organic ion-molecule reactions in the gas phase a n d to report quantitative measurements of the intrinsic kinetics of the reactions of the oxide radical ion, 0-, and the hydroxide ion, OH-, with unsaturated hydrocarbon molecules, a n d of the reactions of carbanions with molecular oxygen. Rate constants a n d product channels for these reactions have been measured directly a n d intrinsic reactivities have been calculated. T h e results indicate tha t in most cases the reactions of 0a n d OHwith olefins proceed extremely rapidly a n d efficiently in the gas phase. T h e reactions of the carbanions with oxygen provide a measure of the intrinsic stability of these ions. I t is expected tha t such information will facilitate the understanding a n d possibly the prediction of modes of acid-base a n d carbanion reactions in solution. (1) National Research Council of U. S. Postdoctoral Research Associate, 1967-1969. Address correspondence to this author at the Department of Chemistry, York University, Toronto 12, Ontario, Canada. (2) National Institutes of Health (Fellowship No. 5F02GM31718-02, National Institute of General Medical Sciences) Postdoctoral Fellow, (3) J. I . Brauman and L. K. Blair, J . Amer. Chem. Soc., 90, 5636, 6561 (1968). (4) T. 0. Tiernan and B. M. Hughes, Proceedings of the 17th Annual Conference on Mass Spectrometry and Allied Topics, Dallas, Texas, May 1969, p 208. 1968-1970. Experimental Section Apparatus and Reagents. A flowing afterglow system has been utilized in this laboratory for several years principally for the investigation of thermal energy ion-molecule reactions of interest in the earth's ionosphere. The description and application of this technique with reference to these studies have been reported in detail previously.6 Since the present paper deals with the novel application of the technique to negative-ion organic chemistry in the gas phase, a brief outline with reference to these investigations is felt to be appropriate. A schematic diagram of the apparatus is shown in Figure 1. The flow system is a stainless steel tube about 100 cm long with an internal diameter of 8 cm. A fast gas flow with a velocity of about lo4 cm/sec is established in the tube by a Roots-type pump backed by a mechanical forepump. Helium is normally used as a carrier or buffer gas. With a helium flow of 180 atm cm3/sec and maximum pumping speed, the helium pressure in the tube is typically about 0.4 Torr. Negative ions are produced either directly in the excitation region by ionizing the parent gas of the ion with 100-eV electrons or indirectly by secondary reaction downstream from the excitation region. In the present experiments pure oxygen was introduced into the excitation region cia source gas inlet 1. The 0ion is then produced by the dissociative ionization reaction e + O2 + 0+ O+ + e (1) and, probably to a much lesser extent, the dissociative attachment reaction

The Interaction of Photo-Excited Chlorophyll a with Duroquinone, α -Tocopherylquinone and Vitamin K 1

Abstract: The reversible electron transfer between photoexcited chlorophyll a and duroquinone has been studied in neutral, acid and alkaline ethanolic solutions. Rates for the reaction of chlorophyll a singlet and triplet states with duroquinone have been determined, and the kinetics for the decay of the radicals so formed have been investigated. In neutral and alkaline solution, evidence has been found for the recombination of the chlorophyll radical cation with the semiquinone radical anion of duroquinone at a rate close to that for a diffusion controlled reaction. In acidic solutions, the chlorophyll radical cation decays by two pro­cesses: 60% reacts by second-order process within milliseconds, and the residual 40% decays by the first-order process having a lifetime of approximately 1 s. The decay rate of these oxidized chlorophyll a species is greatly increased by durohydroquinone. Analogous reactions have been found for triplet chlorophyll a with α -tocopherylquinone and with vitamin K 1 .

Mass spectra of benzotriazoles. Correlation with thermolytic and photolytic fragmentations

Abstract: The mass spectra of some alkyl, aryl and acyl benzotriazoles are reported and discussed on the basis of their thermolytic and photolytic fragmentation products. All benzotriazoles so far studied lose a molecule of nitrogen to give the intermediate radical cations upon electron-impact. Subsequently cyclization and a hydrogen migration lead them to the molecular ions of thermolytic and photolytic fragmentation products. A general rule for predicting the possibility of 1-3 hydrogen migration, based on a knowledge of the electronic state of the radical cation is proposed.

Pulse radiolysis of selenium-containing radioprotectors. I. Selenourea.

Abstract: SummaryThe reactivity of the protective agent, selenourea, towards the primary radicals of water radiolysis, OH, H and the hydrated electron, has been measured by the pulse-radiolysis technique. The radical reactivity of the selenium-, sulphur- and oxygen-containing areas is compared with the radioprotective efficiencies of these compounds: the most efficient radical scavenger, selenourea, is the most efficient protective agent.Both the OH radical and the hydrogen atom give rise to the same radical species when reacting with selenourea. The radical formed by this reaction has a strong absorption band at 410 nm, and it is shown to be a charged complex involving two selenourea molecules. The formation and decay kinetics of this radical ion have been measured together with the association/dissociation constant of the complex. On a radical-scavenging mechanism, the ability of a secondary radical to form a complex may have some bearing on the protective efficiency of the parent compound.The selenourea system h...

Electronic Spectra of Radical Ions

Abstract: Organic molecules may accept an extra electron to form radical anions, R+, or give up an electron by ionization to form radical cations, R+. Some of the radical ions are relatively stable in their ground states in solution phase and can be readily characterized by spectroscopic methods. Electron spin resonance spectroscopy provides an ideal tool for the study of the unshared electron in these radical ions. Most radical ions are intensely colored and give characteristic absorption bands in the electronic spectra. Further, electronic spectroscopy is one of the few tools available for the study of the dianions, which are generally diamagnetic. Electronic spectroscopy is used not merely for the characterization of the ionic species in solution but also for the study of the chemical equilibria involving various kinds of ionic species.

Electron-impact studies—LIV: The formation of [C13H9]+ in the mass spectra of benzyl phenyl ketoxime and 2,3-diphenyl-2-H-azirine†

Abstract: The formation of m/e 165 in the spectrum of benzyl phenyl ketoxime involves the intermediacy of a rearranged 2,3-diphenyl-2-H-azirine radical ion. 2H and 13C labelling of the ketoxime together with 2H labelling of the azirine has allowed certain proposals to be made concerning the complex processes producing m/e 165 in both spectra. The mode of formation of m/e 167 in the spectrum of benzyl phenyl ketoxime has also been studied.

Electron spin resonance study of radicals photolytically generated from aromatic carbonyl compounds. Part III. Reduction of fluorenone and benzophenone in amines

Abstract: E.s.r. spectra of the 9-hydroxyfluorenyl radical, which is produced by the u.v. photolysis of fluorenone in tertiary amines, are presented and discussed. Tertiary amines appear to have a vital and unique role in the reduction process as the 9-hydroxyfluorenyl radical was not observed in photolysed solutions of fluorenone in other amines or in many non-amine solvents. Reduction probably occurs by electron transfer from the nitrogen atom to the excited carbonyl group to form the fluorenone radical anion which then rapidly abstracts a proton from the amine radical cation.Amines can effect markedly the e.s.r. spectra of hydroxy-substituted radicals. Results on the Ph2ĊOH radical in various amine solvents are presented and compared with results for the same radical in solvents in which the effects of solvation are likely to be minimal. Such solvents are cyclohexane and toluene. In the latter, the spectrum of the benzyl radical, PhĊH2, is clearly resolved in addition to that for the Ph2ĊOH radical. The observations can be explained in terms of solvation via hydrogen bonding between the hydroxy-group protons and the nitrogen atom of some amines. Triethylamine appears to be a particularly potent solvator and affects the coupling constants to the hydroxy-protons and, in the case of the 9-hydroxyfluorenyl radical, the ring proton coupling constants quite drastically.

Unstable intermediates. Part LXXIV. An electron spin resonance study of the optical and radiation damage of poly-(2,6-dimethylphenylene oxide)

Abstract: The e.s.r. spectra of u.v.- and γ-irradiated poly-(2,6-dimethylphenylene oxide) in solution and in the solid state have been interpreted in terms of the formation of a dimethylphenoxyl radical (I) as the only major radical. In benzene at room temperature the magnetic parameters for this radical are gav= 2·0047, aMe(I)= 6·2 G, aMe(II)= 5·1 G, and aH(ring)= 1·1 G. In the solid polymer the same radical has effectively isotropic coupling of 5·7 G to the two nearly equivalent methyl groups and g⊥= 2·0024, g∥= 2·0063. At 77 K, after radiolysis in air, the characteristic spectrum of peroxyl-radicals (RO2·) was observed, but irradiation of polymer under vacuum yielded radical (I) together with at least two other radicals. Dipolar interaction between radical pairs has been inferred from the presence of a signal, at g= 4. Radical (I) was present in low concentration even before exposure to radiation, which may mean that it is an intermediate in the synthesis of the polymer.

ESR Studies of Deuterated dl‐Tartaric Acid X Irradiated at 195°K

Abstract: Using electron spin resonance techniques, the free radical produced when single crystals of deuterated dl‐tartaric acid are irradiated at 195°K with either 50 kV x rays or 3 meV x rays was shown to be ·CHODCHODCOOD·D2O. The C–C bond to the carboxyl group is broken and the unpaired electron is primarily in a 2pπ orbital on the carbon atom with the p orbital close to the normal to the carbon plane. This results in a hyperfine coupling to two H atoms with eigenvalues of − 33.4, − 23.0, − 10.7 G for the α‐H hydrogen, and 37.2, 35.8, 30.5 G for the β − H. This radical is the same radical that is observed if deuterated dl‐tartaric acid is irradiated at 77°K and allowed to warm to 195°K. This radical follows the decay of the cation radical produced at 77°K and subsequently decays to the stable room temperature radical. The anion radical which was observed at 77°K is still present at 195°K.

Mass Spectral Characteristics of Pivalolactone and Polypivalolactone

Abstract: The mass spectral characteristics of pivalolactone and its polymer have been determined. The monomeric lactone (MW 100) shows no molecular ion peak but does show peaks at 70 and 42 m/e associated with the loss of formaldehyde and then carbon monoxide and at 56 and 41 associated with the loss of isobutene and carbon dioxide. Only weak peaks, corresponding to the presence of traces of oligomers, are observed above m/e 71. The polymer, at volatilization temperatures of 250-350°C, gives fragments of up to 1242 m/e with a pattern recurring over intervals of 100 m/e units. The principal peaks occur at X42, X70, X83, and X01 m/e. Above 301, the X42 and X70 peaks are observable up to X = 12. The X70 fragment is assigned an acylium isobutyrate radical ion structure and the X42 fragment is assigned an isobutyl radical ion structure. The degradation products are accounted for as being formed from volatilized cyclic oligomers.

Radical Anions Derived from Alkyl-substituted 1,2,4,5=Tetrazines

Abstract: A new series of dialkyl-tetrazine radical anions has been prepared by a disproportionation reaction in basic Me2SO, the mechanism apparently involving formation of two radical anion species, which have been detected in one case

Matrix isolation of thymine radicals in γ-irradiated alkaline ice matrices

Abstract: E.s.r. techniques have been used to study the reactions of thymine, thymidine and dihydrothymine with electrons and O– radical ions which are produced in the γ-irradiation of frozen aqueous solutions of sodium hydroxide. Electrons can attack thymine at the 5,6 double bond when after proton transfer the thymine radical is produced and an eight-line e.s.r. spectrum is observed. After annealing at temperatures above 77 K the O– radical ion can react with the methyl group at the 5 position. In thymidine the eight-line e.s.r. spectrum is observed already at 77 K and this increases further in intensity on annealing. The O– presumably reacts with the methyl group of dihydrothymine.

Decomposition photosensibilisee de solvants organiques a 77°k par une amine aromatique, la diphenylparaphenylenediamine*

Abstract: — –By esr we have studied the photoexcitation of an aromatic amine to its triplet state at 77°K, its photoionization to a radical cation and the simultaneous formation of solvent radicals proceeding from the photosensitization of the organic glassy matrix In the case of methanol and ethanol matrix we observe approximately one solvent radical per solute radical cation In the case of isopropanol and methyltetrahydrofuran we find respectively three and two solvent radicals per solute radical cation The results suggest two possible processes of photosensitization By successive absorption of two photons, the amine reaches an excited triplet state which is able either to dissociate giving one electron and one cation radical or to transfer its energy to the solvent, this last being decomposed It is assumed that in the case of methanol and ethanol, the radicals from the solvent are only formed by reaction on the matrix by the released electron, whereas in the case of isopropanol and methyltetrahydrofuran, the second process is prevalent or exclusive

Kinetics of oxidation of dimethyl sulphoxide by tervalent manganese

Abstract: Kinetic evidence is presented for the reversible formation of a radical ion from Me2SO on oxidation by Mn3+, which initiates polymerisation of acrylonitrile that is terminated by the oxidant.

Catalytic Activity and Reactivity of Aromatic Nitrile and Alkali Metal Ion Radical Salt. I. Homogeneous and Heterogeneous Catalysis of Benzonitrile-Cesium Ion Radical Salt

Abstract: Homogeneous and heterogeneous mechanisms of parahydrogen conversion and hydrogen-deuterium exchange reactions were investigated in the presence of benzonitrile–cesium ion radical salt. Studies of their activation energies and rate constants showed that the heterogeneous reaction on the solid-ion radical salt occurs mainly through the “chemisorption mechanism” and the “exchange mechanism”, but the homogeneous reaction over the salt solution in benzonitrile takes place only through the “physical mechanism.” According to these results, it was concluded that the catalytic activity and reactivity of the ion-radical salt must be due to the nature of its solid phase, not to that of its aromatic anion or free-ion radical pair.