Detection of the triple ion (durosemiquinone-Na<sub>2</sub>)<sup>+</sup> by electron spin resonance spectroscopy

Gough, T. E.; Hindle, P. R.

doi:10.1139/v69-280

Cited by 31 publications

(7 citation statements)

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“…Kabanov assigned the enhancement of polymerization rate of fully ionized acrylic acid upon further increasing cation concentration to the formation of triple ions with a counter cation being located between the carboxylate groups of the monomer and of a moiety sitting next to the radical functionality of the growing chain . The hypothesis of triple ion formation has been supported by EPR studies . The formation of ion pairs, as proposed in the preceding text, may however also account for the observed effects on polymerization rate of different types and amounts of alkali cations and would reduce the molecularity of the propagation step from a termolecular to a bimolecular reaction.…”

Section: Influence Of the Type Of Counter Cation On Rpmentioning

confidence: 82%

Radical Polymerization of Alkali Acrylates in Aqueous Solution

Drawe

Buback

Lacı́k

2015

Macro Chemistry & Physics

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Monomer conversion versus time profi les for the radical polymerization of ionized acrylic acid (AA), 0.6 to 0.8 mol L −1 in aqueous solution, are measured at 50 °C via inline near-infrared spectroscopy mostly on fully ionized AA, i.e., of alkali acrylates. Ionization reduces polymerization rate with the size of this effect being dependent on the type and on the concentration of the alkali counter cation, which is varied from lithium to rubidium. Polymerization rate becomes very small upon shielding the cation by complexation, whereas an enhancement of cation concentration, by addition of alkali chloride, may enhance polymerization rate such as to even reach the high rates observed with the radical polymerization of nonionized AA. by approximately one order of magnitude in passing from nonionized to fully ionized AA. Here and in the following sections, the notifi cation "fully ionized" refers to an equimolar ratio of hydroxide and acid (for the titration curve see the Supporting Information). Further addition of sodium hydroxide results in an increase of r p . These early data were derived from rotating sector investigations into the individual rate coeffi cients of propagation, k p , and termination, k t . The increase of r p with pH and with cation concentration was assigned primarily to k p , whereas k t stays constant according to a so-called ion-pair concept, which actually is an anion-cation-anion complex. [ 4,5 ] The changes of AA k p were confi rmed by Lacík et al. [ 7 ] via pulsed laser polymerization (PLP) experiments carried out in conjunction with size-exclusion chromatography (SEC) to provide k p values as a function of α for polymerizations of 0.69 mol L −1 AA in aqueous solution at 6 °C. Investigations into AA polymerization at different temperatures and degrees of ionization via 1 H-NMR and SEC by Cutié et al. [ 6 ] showed that the number-average molar mass, M n , and the propagation rate, r p , follow similar trends: M n decreases with increasing α and increases again upon further addition of alkali hydroxide. Measurements at an initial monomer content as high as 37 wt% revealed that increasing monomer concentration

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Section: Influence Of the Type Of Counter Cation On Rpmentioning

confidence: 82%

Radical Polymerization of Alkali Acrylates in Aqueous Solution

Drawe

Buback

Lacı́k

2015

Macro Chemistry & Physics

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“…1 broadening of the septets. Identical correlations were found for triple ions formed between sodium and a series of semiquinones (2), though for these semiquinone systems the amount of broadening is much larger.…”

Section: Discussionmentioning

confidence: 97%

Electron spin resonance spectra of the triple ions [Na₂-pyrazine]⁺ and [Na₂-tetramethylpyrazine]⁺

Al-Baldawi¹,

Gough²

1970

Can. J. Chem.

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Reduction of pyrazine (P) and tetramethylpyrazine (TMP) by sodium in the presence of sodium tetraphenylboride produces Na2P+ and Na2TMP+, respectively. The electron spin resonance spectra of these species are presented and compared with those of the corresponding ion pairs. From linebroadening effects within the sodium hyperfine multiplets of the triple ion spectra, it is deduced that the sodium ions occupy positions close to the N-N axes of the ring systems. IntroductionThe detection, by electron spin resonance spectroscopy, of triple ions of the formula Na,Q+ has been reported (1, 2) for Q equals p-benzoquinone, 2,3-, 2,5-, 2,6-dimethyl-p-benzoquinone, and duroquinone. The proton hyperfine splitting constants of the triple ion indicate that one sodium associates with each oxygen of the semiquinone. Molecular tumbling does not completely average the anisotropies within the hyperfine and g tensors of the triple ion with the result that asymmetric broadening of the sodium hyperfine septets was observable. From this broadening it was deduced (2) that the sodium ions occupy positions close to the 0-0 axis of the semiquinone. It is of interest to determine whether these effects are limited to semiquinones, or whether the experiment has more general application to the structure of other ionic associates.A number of papers (3-10) have concerned themselves with the structure of ion pairs formed between pyrazine anions and alkali metal cations. The observation of line-width alternation for sodium-pyrazine in tetrahydrofuran (4) and 1,2-dimethoxyethane and of two non-equivalent nitrogen nuclei for lithium-pyrazine in tetrahydrofuran (5) makes it clear that these cations associate with one of the nitrogens of pyrazine, rendering the anion asymmetric. Calculations on the structure of these ion pairs (5,8,10) indicate that at realistic interionic distances the most stable position for the cation is above the center of the pyrazine ring, which obviously does not agree with the experimental results. Calculations on the structure of the protonated pyrazine anion (9) predict an asymmetric structure with the proton

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“…When the reduction is performed in the presence of an equimolar quantity of sodium tetraphenylboride, the e.s.r. spectra indicate the presence of Na,D', provided that the polarity of the solvent is sufficiently low (4). At higher polarities, e.g.…”

Section: Introductionmentioning

confidence: 98%

Electron spin resonance spectra of triple ions: anisotropic effects in the hyperfine splitting patterns of ²³Na counter-ions

Gough¹,

Hindle²

1969

Can. J. Chem.

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The formation, in tetrahydrofi~ran, of triple ions of the formula NalQ+ (Q = p-benzosemiquinone, 2,3-, 2,5-, 2,6-dimethyl-p-benzosemiquinone, durosemiquinoi~e) has been detected by electron spin resonance spectroscopy. The spectra show asymmetric broadening within the Z3Na hyperfine multiplets. From the direction of this broadening, it is deduced that the sodium ions lie in the plane of the semiquinone anion, one sodium ion associating with each oxygen.Canadian Journal of Chemistry, 47. 3393 (1969) IntroductionThe one-electron alkali metal reduction of duroquinone (D) in ethereal solution forms durosemiquinone (D-); the electron spin resonance (e.s.r.) spectra of the reaction products indicate extensive ionic association in such media (1-3) though, especially at low temperatures, an equilibrium exists between M' D -and its constituent ions. The reactions which constitute the equilibrium are sufficiently slow that well resolved spectra for M' D-and for D -are obtained. When the reduction is performed in the presence of an equimolar quantity of sodium tetraphenylboride, the e.s.r. spectra indicate the presence of Na,D', provided that the polarity of the solvent is sufficiently low (4). At higher polarities, e.g. in 1,2-dimethoxyethane, the spectra indicate the presence of intermolecular cation exchange reactions, though a complete interpretation of these spectra has not been achieved.The polarity of the solvent is not the only factor controlling the formation of triple ions. Listed below are several systems in which strong ionic association occurs, yet triple ions are not observable. All of the following systems contain a semiquinone anion and excess sodium cations dissolved in a solvent of low polarity : 9,lO-anthrasemiquinone and sodium iodide in 1,2-dimethoxyethane (5), 9,lO-anthrasemiquinone and sodium tetraphenylboride in tetrahydrof~~ran (6), 2,5-dit-butyl-p-benzosemiquinone and sodium iodide in tetrahydrof~lran (5), duroserniquinone (7) and 2,6-dimethyl-p-benzosemiquinone (8), and sodium t-pentoxide in t-pentanol.As part of an experimental survey on the

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Detection of the triple ion (durosemiquinone-Na₂)⁺ by electron spin resonance spectroscopy

Cited by 31 publications

References 5 publications

Radical Polymerization of Alkali Acrylates in Aqueous Solution

Radical Polymerization of Alkali Acrylates in Aqueous Solution

Electron spin resonance spectra of the triple ions [Na₂-pyrazine]⁺ and [Na₂-tetramethylpyrazine]⁺

Electron spin resonance spectra of triple ions: anisotropic effects in the hyperfine splitting patterns of ²³Na counter-ions

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Detection of the triple ion (durosemiquinone-Na2)+ by electron spin resonance spectroscopy

Cited by 31 publications

References 5 publications

Radical Polymerization of Alkali Acrylates in Aqueous Solution

Radical Polymerization of Alkali Acrylates in Aqueous Solution

Electron spin resonance spectra of the triple ions [Na2-pyrazine]+ and [Na2-tetramethylpyrazine]+

Electron spin resonance spectra of triple ions: anisotropic effects in the hyperfine splitting patterns of 23Na counter-ions

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Detection of the triple ion (durosemiquinone-Na₂)⁺ by electron spin resonance spectroscopy

Electron spin resonance spectra of the triple ions [Na₂-pyrazine]⁺ and [Na₂-tetramethylpyrazine]⁺

Electron spin resonance spectra of triple ions: anisotropic effects in the hyperfine splitting patterns of ²³Na counter-ions