Showing papers on "Radical ion published in 1974"

The crystal structure of the 1:1 radical cation–radical anion salt of 2,2'-bis-l,3-dithiole (TTF) and 7,7,8,8-tetracyanoquinodimethane (TCNQ)

Abstract: The salt of the radical cation of 2,2'-bis-l,3-dithiole (TTF) and the radical anion of 7,7,8,8-tetracyanoquinodimethane (TCNQ), C18HaN4S4, crystallizes in the monoclinic system, space group P2~/c, with cell constants: a= 12.298 (6), b=3\"819 (2), c= 18\"468 (8) /~, fl= 104\"46 (4) °, Z=2, Dm= 1\"62 (1) and Dc=1\"615 g cm -3. Intensities for 1373 independent reflections were collected on an automated diffractometer. The structure was solved by standard heavy-atom methods and has been refined by fullmatrix least-squares calculations to an R value of 0\"044. The TTF radical cations and the TCNQ radical anions form homologous columnar stacks with interplanar spacings of 3.47 and 3.17 A, respectively. The dihedral angle between the least-squares planes of the cations and the anions is 58.5 ° and is approximately bisected by [010].

Electrochemically Generated Colored Films of Insoluble Viologen Radical Compounds

Abstract: Electrochemical reactions that produce a change of light absorption in the visible region can be used in display devices. The reduction of the 4,4'‐di‐pyridinium compounds or viologens to stable blue radicals is very promising in this respect. It was found that in aqueous solution the solubility of the radical is remarkably lower than that of the oxidized form. It turned out that the solubility depends on the kind of anion and the magnitude of the viologen radical ion.

Ubiquitous trisulphur radical ion S 3

Abstract: THE colour of blue ultramarine and the deep blue colour of alkali polysulphides in electron pair donor solvents have been attributed to the disulphur radical ion, S2−· (ref. 1). That assignment is erroneous and I here establish the correct identity of the species, emphasise the variety of situations in which it is encountered and point out its possible role as an intermediate, in transformations involving elemental sulphur, or sulphide ions.

Electrodeposition of tin, lead and tin-lead alloys

Abstract: A bath for the electrodeposition of bright tin-lead alloys which comprises an aqueous acidic bath containing at least one soluble tin compound and one soluble lead compound to which there has been added: A. a lower alkylene oxide condensation product, and B. an effective amount of at least one pyridine or quinoline compound having the structure ##STR1## wherein the substituents R1, R2, R3, R4 and R5 each is a hydrogen or halogen atom, a lower alkyl radical containing a hydroxyl group, an alkenyl radical, the radical (Cn H2n --CO2 H in which n has a value from 0 to 6 or a carbamide radical or R4 and R5 combined form a divalent radical to provide a compound having the structure ##STR2## in which R6 is nothing or a hydroxyl radical; Z is nothing, 0- or a quaternary ammonium forming hydrocarbon radical provided that when Z is nothing, at least one of the substituents R1, R2, R3, R4 and R5 is a halogen atom, a lower alkyl radical containing a hydroxyl group, an alkenyl radical, the radical (Cn H2n --CO2 H in which n has a value from 0 to 6 or a carbamide radical or R6 is a hydroxy radical; and X is nothing or when Z is a quaternary ammonium forming hydrocarbon radical X is an anion. The invention also includes the addition of an aromatic aldehyde in combination with pyridine or quinoline compounds and the alkylene oxide condensation product which results in the production of even brighter to brilliant deposits over a wide current density range.

pH Effects on the pulse radiolysis of deoxygenated aqueous solutions of sulphur dioxide

Abstract: Dilute deoxygenated aqueous solutions of sulphur dioxide and its related anions HSO–3 and SO2–3 in the pH-range 2–11 were pulse irradiated and the time dependence of the transient optical absorptions and electrical conductance recorded. Hydrogen atoms and OH radicals abstract hydrogen from HSO–3. Also OH radicals react with SO2 and SO2–3 to form the radical ion SO–3˙ with an absorption maximum at 255 nm. The SO–3˙ radical ions recombine to form sulphate (SO2–4) and dithionate (S2O2–6), the reaction rate and relative proportions of products being pH-dependent. In acid solutions the SO–2˙ radical ion with an absorption maximum at 360 nm is also formed, presumably by reaction of hydrogen atoms with sulphur dioxide. The SO–2˙ radical ions recombine to form dithionite (S2O2–4).

ESR study of free radicals in irradiated single crystals of potassium hydroxylamine disulfonate

Abstract: Two free radicals formed when single crystals of potassium hydroxylamine disulfonate are irradiated with gamma rays at 77°K were studied by ESR. The ESR spectra result from a predominant center (radical A) exhibiting large 14N and 1H hyperfine splittings and from lesser amounts of Fremy's radical [ȮN(SO3)22−]. The g and hyperfine tensors of these radicals have been evaluated and are discussed. Radical A, whose identity remains in doubt, may be regarded as the precursor to Fremy's radical; on warming its lines decay and those of Fremy's radical are formed. Lines from radical A decrease in strength and those of the hydroxyl radical (ȮH) grow in strength when irradiated crystals are photolyzed at 77°K. The reverse reaction occurs in the dark; the hydroxyl radical disappears and radical A is reformed.

Solute ion and radical formation in the pulse radiolysis of acetonitrile solutions

Abstract: Following microsecond pulse radiolysis of solutions of a variety of solutes in acetonitrile, absorptions assigned to solute cation radicals, anion radicals, excited states and neutral radicals are observed. Pulse radiolysis of solutions of tri-p-tolylamine or triphenylamine yields the amine radical cations, whose absorptions are observed to grow-in by a second-order process after the electron pulse. We report rate constants for this process, which is suggested to be electron transfer to acetonitrile radical cation or cation dimer. Yields of G∼0.2 are reported for the oxidizing species. Oxidation via a different route involving hydrogen atom transfer is suggested to occur following pulse radiolysis of solutions of phenol or phenothiazine. Pulse radiolysis of solutions of benzophenone or biphenyl yields the solute radical anions in agreement with previous studies on this system. The mechanism of acetonitrile radiolysis is discussed with a consideration of this and previous studies.

Radiation-induced crosslinking and cyclization in 1,2-polybutadiene

Abstract: In order to get information on the radiolytic changes in 1,2-polybutadiene (1,2-PB) the sol and gel fractions, the conversion of double bonds, the structure and concentration of radicals, the formation of dienes and the formation of gaseous products were measured. In addition, the dose rate dependence and temperature dependence for the conversion of double bonds were determined. G values for double bond conversion depend on molecular weight and range from 20 to 200. G values for crosslinking are about 10. A mechanism for the double bond conversion is proposed which involves initiation by a transformation of the primary radical ion in the vinyl group into a carbonium ion and a radical. This is supported by ESR measurement. Reaction of the carbonium ion with a vinyl group in the same chain gives rise to cyclization, whereas reaction with a vinyl group in a neighboring chain results in crosslinking. A comparison of the G values for conversion of double bonds with the G values for crosslinking shows that the formation of cyclic rings exceeds the formation of crosslinks by a factor of about 10. The corresponding values in 1,4-cis- and 1,4-trans-polybutadiene are much smaller [G(cl) ≃ 2; G(db) ≃ 7]. The pendent vinyl groups in 1,2-polybutadiene therefore are more reactive than the vinylidene groups in 1,4-polybutadienes.

Electron spin resonance identification of the dimer radical cation (CH3O)3P-P(OCH3)3/+ in γ-irradiated trimethyl phosphite from second-order hyperfine structure

Abstract: A dimer radical possessing two anisotropically equivalent phosphorus atoms has been conclusively identified in γ-irradiated trimethyl phosphite, its E.S.R. spectrum consisting basically of four lines due to the large second-order splitting of the central component. In the powder spectrum of the γ-irradiated glass the central features are obscured by overlapping signals from other radicals. However, the downfield (1, 0) feature was clearly revealed by suppressing the formation of the interfering P(OCH3)2 radical through the inclusion of methyl bromide in the sample. The E.S.R. spectrum of a γ-irradiated single crystal is very well resolved and three complete sets of lines can be assigned unequivocally to chemically non-equivalent dimers. The spectra of two of the dimers undergo site splitting such that the symmetry elements for each pair of magnetically distinguishable sites are related. In addition, each of the lines belonging to these two dimer spectra is flanked by a pair of ‘spin-flip’ satellites at hi...

Involvement of the superoxide free radical ion in photosynthetic oxygen reduction.

Abstract: Abstract Photosynthetic oxygen reduction by isolated chloroplast lamellar systems has been studied with the aid of superoxide dismutase. Two mechanisms of oxygen reduction by illuminated chloroplast lamellar systems can be differentiated: 1. In the presence of low potential electron acceptors like AQ or MV the superoxide free radical ion is the product of autooxidation of the reduced acceptor. Addition of superoxide dismutase has no influence on the initial rates of oxygen reduction. 2. Stimulation of photosynthetic oxygen reduction by o-diphenols is only observed in the absence of superoxide dismutase and ascorbate; apparently the superoxide free radical ions is involved in both initiation and propagation of a chain reaction. If the ferredoxin-stimulated photosynthetic oxygen reduction is measured, both ascorbate and superoxide dismutase are active as inhibitors. By heating suspensions of chloroplast lamellar systems, a substance is released into the supernatant which exhibits the activity of an oxygen reducing factor (ORF) with properties similar to o-diphenols: The stimulation of photosynthetic oxygen reduction is reversed by addition of either SDM or ascorbate. A reaction sequence for photosynthetic oxygen reduction in the presence of ferredoxin is considered, which is initiated by the superoxide free radical ion produced by autooxidation of reduced ferredoxin; the superoxide free radical ion \"activates\" an endogenous oxygen reducing factor, which in this \"active\" state can reduce oxygen to O2·-. The presence of either superoxide dismutase or ascorbate yields in chain termination by scavenging the superoxide free radical ion

Alkali N.M.R. experiments on the radical ion pairs of biphenyl and fluorenone

Abstract: Line widths in the 6Li, 7Li, 23Na, 39K, 85Rb, 87Rb and 133Cs N.M.R. spectra of solutions of the alkali salts of biphenyl and fluorenone are reported as a function of solvent and temperature. From a numerical analysis of the room temperature data the contribution of the various relaxation mechanisms to the line widths are established. It is shown that the results are consistent with the observed solvent and temperature dependence of the line widths. Values of the electron spin correlation time are obtained and a value of 1·6 ± 0·4 A is found for the ‘Van der Waals radius’ of the biphenyl anion. Line width expressions for the static and the dynamic ion pair model are presented. It is demonstrated that the static ion pair model applies to solutions of caesium biphenylide. Semi-empirical rules are presented concerning the importance of various relaxation mechanisms for the different alkali nuclei in the type of solution studied here.

Magnetic Property and Electronic Structure of Tris(2,2′-bipyridine) Complexes of Manganese in Low Oxidation States

Abstract: The magnetic susceptibilities of tris(2,2′-bipyridine)manganese complexes, [Mn(bpy)3]·2THF and Li[Mn(bpy)3]·4THF (THF: tetrahydrofuran), have been determined over a temperature range of 1.6–320 K. The susceptibility of Li[Mn(bpy)3]·4THF can be explained with a radical ion model, in which three 2,2′-bipyridine radical ions are coordinated to a manganese(II) ion. A similar model is applicable to [Mn(bpy)3]·2THF as well. The presence of antiferromagnetic interaction indicates the formation of a weak covalent bond between manganese and bipyridine. This can be elucidated consistently by the molecular orbital theory.

Free radicals in pyrimidines: ESR of x-irradiated 5-ethylbarbituric acid and its potassium salt

Abstract: Irradiation of 5‐ethylbarbituric acid yields a free radical formed by hydrogen abstraction from C(5) of the pyrimidine ring. The characteristics of this radical are similar to those of the same radical formed by abstraction of an ethyl group from 5, 5‐diethylbarbituric acid. There is no evidence of an ethyl abstraction radical in this compound, indicating that the abstraction of the hydrogen rather than the ethyl is highly preferred. Irradiation of the potassium salt of 5‐ethylbarbituric acid yields a free radical formed by hydrogen abstraction from the ethyl group. Principal values are as follows: g1=2.0032, g2=2.0031, g3=2.0025, A1H = 26.4 G, A2H = 16.5 G, A3H = 10.9 G, A1CH3 = 21.0 G, A2CH3 = 20.5 G, A3CH3 = 19.6 G. Only one molecule per unit cell was observed magnetically, although the crystal structure would indicate that two or three should be seen. The formation of this hydrogen abstraction radical is surprising because a simple ionization of the parent molecule would yield the very stable radical ...

Electron-impact fragmentation of triaryl-s-trithianes: a novel skeletal rearrangement involving sulphur-sulphur bond formation

Abstract: The mass spectral fragmentation of seven substituted 2,4,6-triaryl-s-trithianes has been studied and the fragmentation modes confirmed by deuterium labelling. Triphenyl-s-trithiane shows some interesting features in its mode of cleavage and does not eliminate S, S 2 , SH ⋅ , H 2 S or S 2 H ⋅ from its molecular ion. The prominent radical ions in the mass spectrum are at m/e 180 (52.3%) and m/e 186 (45.2%), corresponding to stilbene and PhCHS 3 . Their compositions have been established by deuterium labelling and accurate mass measurements. The formation of stilbene indicates a relationship between pyrolytic and electron-impact studies. The origin of [PhCHS 3 ] +⋅ suggests that one of the sulphur atoms attaches itself to the other two sulphur atoms in the molecular ion, eliminating a stilbene radical ion. The other important fragmentation corresponds to the monomer radical ion (thiobenzaldehyde) and the thiobenzoyl cation. Among the other substituted triaryl-s-trithianes with substituents such as chloro, methoxy, methylenedioxy and hydroxy groups on the phenyl ring (IV to IX), only the tris-(p-chlorophenyl)-s trithiane shows an insignificant molecular ion. Unlike the triphenyl derivative, the chloro, methoxy and methylenedioxy derivatives show the loss of HS ⋅ and/or H 2 S from the molecular ion. The spectrum of tris-(p-hydroxyphenyl)-s-trithiane corresponds to the spectrum of p-hydroxythiobenzaldehyde.

Optical and esr studies in n-acetyl dl-methionine single crystals γ-Irradiated at low temperature

Abstract: N-acetyl DL-methionine single crystals are irradiated with 60Co γ-rays or x-rays at LNT and LHeT in the dark The radical cations produced by irradiation are investigated using optical absorption spectrum and esr On irradiation, the observable product is the β radical, the radical cation with a hole in a nonbonding orbital of the sulfur atom, which has three bands, ie, b1 (730 nm), b2 (350 nm) and c (450 nm) bands By annealing and photoillumination experiments, the p radical is transformed to the other isomers β* and β**, slightlr different in the electronic structure and conformation, which have b* 1 (630 nm), b* 2 (330 nm) and b** 1 (570 nm), b** 2 (300 nm), respectively In addition, photo induced hole transfer β to β' (the hole in a π-orbital of carboxyl group) and the reverse process by thermal annealing were observed using optical absorption as well as esr It is also observed that the β radical decays when photo illuminated in the b1 or b2 band and that the reaction proceeds in first o

Magnetic susceptibility of tris(2,2′-dipyridyl)manganese complexes having an anomalous valency of manganese

Abstract: The magnetic susceptibility of tris(2,2′-dipyridyl)manganese complexes, [Mn(dipy)3] · 2THF and Li[Mn(dipy)3] · 4THF (THF: tetrahydrofuran), has been determined over a temperature range of 1.5–300 K. The susceptibility of Li[Mn(dipy)3] · 4THF can be explained with a radical ion model, in which three 2,2′-dipyridyl radical ions are coordinated to a manganese(II) ion, suggesting the formula [Mn2+(dipy−)3]− rather than [Mn−(dipy0)3]−. A similar model is applicable to [Mn(dipy)3] · 2THF as well.

Radical-ion formation in aromatic amine–tetracyanoethylene systems

Abstract: The kinetics of the formation and decay of the tetracyanoethylene radical anion from aromatic amine–tetracyanoethylene systems in dichloromethane have been studied. A mechanistic scheme to account for the observed reaction products and kinetic order is proposed and reaction with an excess of donor is suggested to be the major pathway within this mechanism.