Electron spin resonance spectrum of tetrakis(p-methoxyphenyl)ethylene cation radical

Valenzuela, Jorge; Bard, Allen J.

doi:10.1021/j100847a054

Cited by 15 publications

(3 citation statements)

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“…Tetraphenylethylene and its ring-substituted analogues are bifunctional electron donors (or acceptors) by virtue of both aromatic and olefinic centers present as either electron-rich (or electron-poor) reservoirs. As such, various tetraarylethylenes have enjoyed widespread application to reaction types as diverse as reduction, oxidation, photocyclization, halogenation, oxygenation, etc. , Especially noteworthy are the highly hindered electron-rich analogues, which are known to result in intensely colored solutions upon treatment with various electrophiles (Cl 2 , Br 2 , I 2 , and ICl) as well as Brønsted and Lewis acids. , …”

Section: Introductionmentioning

confidence: 99%

Disproportionation and Structural Changes of Tetraarylethylene Donors upon Successive Oxidation to Cation Radicals and to Dications

et al. 1998

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The stepwise (one-electron) chemical oxidation of the tetraphenylethylene donor and its substituted analogues (D) can be carried out by electron exchange with aromatic cations or antimony(V) oxidants to selectively afford the cation radical (D +•) initially and then the dication (D 2+). The ready interchange of the latter establishes the facile disproportionation (i.e., 2D +• ⇌ D 2+ + D) that was originally examined by only transient electrochemical techniques. The successful isolations of the crystalline salts of the tetraanisylethylene cation radical (1 +•) as well as the tetraanisylethylene dication (1 2+) allow X-ray diffraction analysis (for the first time) to quantify the serial changes in the molecular structure upon successive oxidations. Five structural parameters (d, l, θ, φ, and q) are identified as quantitative measures of changes in bond (Cα Cβ, Cα anisyl) lengths, dihedral (Cα Cβ)/torsional (anisyl) angles, and quinoidal (anisyl) distortion attendant upon the removal of first one-electron and then another electron from the tetraanisylethylene framework. The linear variation of all five parameters in Chart 3 point to a strongly coupled relaxation of tetraanisylethylene (involving simultaneous changes of d, l, θ, φ, and q) to a severely twisted dication. Most noteworthy is the structure of the cation radical 1 +• with d, l, θ, φ, and q values that are exactly one-half those of the dication. The complex molecular changes accompanying the transformation: D → D +• → D 2+ bear directly on the donor properties and the disproportionation processes of various tetraarylethylenes.

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Section: Introductionmentioning

confidence: 99%

Disproportionation and Structural Changes of Tetraarylethylene Donors upon Successive Oxidation to Cation Radicals and to Dications

et al. 1998

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“…Then it was distilled under nitrogen and stored in the vacuum line. 26 Potassium metal was obtained from Matheson Coleman and Bell. It was stored under mineral oil and was carefully washed with purified solvent at the time of the experiment.…”

Section: Methodsmentioning

confidence: 99%

“…The field sweep was calibrated by using Fremy salt in one side of a V-4532 dual sample cavity. The high-and low-field coupling constants for the Fremy salt were taken as 13.160 ± 0.008 and 13.101 ± 0.004 G. 26 A Moseley 7100 dual channel recorder was used to record the spectra. A Varían V-4540 variable temperature unit was used for low-temperature studies.…”

Section: Methodsmentioning

confidence: 99%

Electron spin resonance studies of hyperconjugation in 2,3-, 2,6-, and 2,7-dimethylanthracene cation and anion radicals

Valenzuela¹,

Bard²

1969

J. Phys. Chem.

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Electron spin resonance spectrum of the diphenylcyclobutene anion radical

Goldberg

1973

Org. Magn. Reson.

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Abstract-The anion radical of 1,2-diphenyIcyclobutene was studied by electron spin resonance. The hyperfine splittings were found to be 0.47 and 0.74G for the metu-positions, 2.23 and 2.69 G for the ortho-positions and 4.21 G for the para-positions of the phenyl rings. The methylene proton splittings were 4.27 G , which would imply that the value of QCOII, is 27 G, much lower than that of other cyclobutene anions. It was also estimated that the angle between the axis of the p-orbitals of the ethylene group and that of the phenyl group is about 30°, in agreement with that found for the tetraphenylethylene anion.THE ANION radical of 1,2-diphenyIcyclobutene (DPCB) is of interest, due to the fact that it is essentially a cisstilbene radical as well as a cyclobutene derivative. cis-Stilbene has been found to convert immediately to the trans-configuration upon reduction to the anion radica1;l however, in this case the anion is locked in the cis-configuration. Studies of naphtho-,2a naphthol , 4 -q~i n o n e~~ and b e n~o -~~?~ cyclobutene anions indicate that the value of QCCHa which relates the hyperfine splittings of the methylene group to the spin density on the trigonial carbon(1) of the cyclobutene [Eqn. (l)], is about 50 Gauss. In the DPCB anion this value appears to be about 27 Gauss.The hyperfine splittings of DPCB are presented in Table 1. There was no significant change in the linewidths or splittings between -70°C and -20°C. Broadening occurred at lower temperatures, which was assumed to be due to viscosity effects and at higher temperatures, which was assumed to be due to exchange effects resulting from the relatively high concentrations needed to obtain a reasonably good signal to noise. The g-factor corrected for second order shifts was 2.00268 & 0.00001.It is found that the ratio of the splittings of the orthopositions for stilbenel"Jb is greater than that of DPCBT, but the same trend is exhibited by the anions of styrene and or-methyl ~tyrene.~ Two molecular orbital models have been used to simulate the inequivalence of the ortlzo-positions of the phenyl rings in Huckel Molecular Orbital (HMO) calculations. The 'P-effe~t'~.~ invokes a resonance between the ortho-position and the carbon atom of the ethylene which is not directly bonded to that phenyl group. The 'or-effe~t'~.~ represents a repulsion between the ethylene and the ortho-position closest to the ethylene, designated by o in the labeling scheme by a change in the coulomb integral of the orfhoposition. In studies of substituted ethylenes, the aeffect has been used most frequently and has been found to give the best agreement with experimental parameters when used in the HMO model. The best values of 6 in the coulomb integral, a = oreo + 6pCCo for the orfho-position that have been used, range between 0.1 5 and 0.20.1b,4,7 In this case a value for 6 of about -0.08* gave the best agreement with spin densities of the phenyl ring calculated from the Colpa-Bolton relationship,s (2) where a, is the proton splitting, Q C H ( 0 ) and K,, are -27 Gauss an...

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Electron spin resonance spectrum of tetrakis(p-methoxyphenyl)ethylene cation radical

Cited by 15 publications

References 2 publications

Disproportionation and Structural Changes of Tetraarylethylene Donors upon Successive Oxidation to Cation Radicals and to Dications

Disproportionation and Structural Changes of Tetraarylethylene Donors upon Successive Oxidation to Cation Radicals and to Dications

Electron spin resonance studies of hyperconjugation in 2,3-, 2,6-, and 2,7-dimethylanthracene cation and anion radicals

Electron spin resonance spectrum of the diphenylcyclobutene anion radical

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