The structure of phenoxyl radicals as studied by 2 mm band ESR

Bresgunov, A. Yu.; Dubinsky, A. A.; Poluektov, Oleg G.; Lebedev, Ya. S.; Prokof’ev, A. I.

doi:10.1080/00268979200100861

Cited by 20 publications

(14 citation statements)

References 8 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…A high-field ESR spectrum of a galvinoxyl radical had been already reported, showing no hyperfine structures. 21 The observed W-band spectrum and the obtained g-tensors are similar to those of other phenoxyl radicals, 15,16 showing that the unpaired electron is delocalized over the ³-conjugated framework. At this point, it can be assumed that the oxygen which is a paramagnetic center in the molecular structures of the generated radicals might form a hydrogen bond with the para-OH or the phenolic OH of the host diamagnetic matrix, primary phenol in the condensed phase and a large part of the unpaired electron spin might be distributed over the OH, resulting in the large doublet 1 H-hyperfine splitting.…”

Section: Resultssupporting

confidence: 64%

Intermolecular Hydrogen Bonds between a Radical and a Diamagnetic Matrix: CW-ESR Investigations of 2,6-Di-tert-butyl-4-hydroxymethylphenol

Yamaji¹,

Saiful²,

Baba³

et al. 2009

Bulletin of the Chemical Society of Japan

View full text Add to dashboard Cite

We propose a novel formation model of an intermolecular hydrogen bond between radicals and a diamagnetic matrix in the condensed phase. W-band and multi-frequency ESR studies revealed that the polycrystalline radical sample generated from PbO 2 oxidation of 2,6-di-tert-butyl-4-hydroxymethylphenol in toluene solution in vacuum at room temperature has an anomalously large 1 H-hyperfine interaction. It was concluded that this interaction is attributed to hydrogen bonding between the O• which is a paramagnetic center in the molecular structure of the radicals and the para-OH or the phenolic OH of the primary phenol. Although the phenol shows interesting radical chemical reactions unlike other 2,6-di-tert-butylphenol derivatives, the generated radical species were successfully defined by the solution ESR investigations. This may be the first ESR observation of an anomalously large hyperfine doublet structure coming from a proton on an intermolecular hydrogen bond between a radical and a diamagnetic phenol.

show abstract

Section: Resultssupporting

confidence: 64%

Intermolecular Hydrogen Bonds between a Radical and a Diamagnetic Matrix: CW-ESR Investigations of 2,6-Di-tert-butyl-4-hydroxymethylphenol

Yamaji¹,

Saiful²,

Baba³

et al. 2009

Bulletin of the Chemical Society of Japan

View full text Add to dashboard Cite

show abstract

“…As seen from Fig. 1b, it is difficult to determine the ESR linewidth due to the inhomogeneously broadened lineshape, which is dominated by g-anisotropy arising mainly from the spin-orbit interaction with the oxygen atom [23]. In this light, we define the linewidth D in this work as the distance from base to base of the ESR spectrum.…”

Section: Resultsmentioning

confidence: 99%

Dissolution DNP-NMR spectroscopy using galvinoxyl as a polarizing agent

Lumata

Merritt

Malloy

et al. 2013

Journal of Magnetic Resonance

View full text Add to dashboard Cite

The goal of this work was to test feasibility of using galvinoxyl (2,6-di-tert-butyl-α-(3,5- di-tert-butyl-4-oxo-2,5-cyclohexadien-1-ylidene)-p-tolyloxy) as a polarizing agent for dissolution dynamic nuclear polarization (DNP) NMR spectroscopy. We have found that galvinoxyl is reasonably soluble in ethyl acetate, chloroform, or acetone and the solutions formed good glasses when mixed together or with other solvents such as dimethyl sulfoxide. W-band electron spin resonance (ESR) measurements revealed that galvinoxyl has an ESR linewidth D intermediate between that of carbon-centered free radical trityl OX063 and the nitroxide-based 4-oxo-TEMPO, thus the DNP with galvinoxyl for nuclei with low gyromagnetic ratio γ such as 13C and 15N is expected to proceed predominantly via the thermal mixing process. The optimum radical concentration that would afford the highest 13C nuclear polarization (approximately 6% for [1-13C]ethyl acetate) at 3.35 T and 1.4 K was found to be around 40 mM. After dissolution, large liquid-state NMR enhancements were achieved for a number of 13C and 15N compounds with long spin-lattice relaxation time T1. In addition, the hydrophobic galvinoxyl free radical can be easily filtered out from the dissolution liquid when water is used as the solvent. These results indicate that galvinoxyl can be considered as an easily available free radical polarizing agent for routine dissolution DNP-NMR spectroscopy.

show abstract

“…Since the ESR intensity of the singlet increased with increasing the concentration of phenol, the singlet is assigned to the phenoxy free radicals, whose isotropic g-value reported (g iso = 2.00463) [16] is very close to that of the singlet. The sextet is most probably butyl free radicals, because the spectral pattern of the sextet is similar to that of the n-butyl free radical produced in c-ray irradiated n-butylchloride [17,18].…”

Section: Free Radicals Assisting Dnp-enhancementmentioning

confidence: 94%