Multi-Frequency ESR Study of the Polycrystalline Phenoxyl Radical of α-(3,5-Di-tert-butyl-4-hydroxyphenyl)-N-tert-butylnitrone in the Diamagnetic Matrix

Abstract

Multifrequency (X-, Q-, and W-band) electron spin resonance (ESR) spectroscopy has been used to characterize the phenoxyl radical produced from alpha-(3,5-di-tert-butyl-4-hydroxyphenyl)-N-tert-butylnitrone, which is a new spin-trapping reagent. The X-band measurement did not resolve the powder-pattern ESR spectrum. Because of its higher resolution with g value, the Q-band ESR study revealed that the g factor has an axial-like symmetry and that the observed hyperfine structure in the Z-direction is caused by the nitrogen nucleus at the para-position. Furthermore, the results of the W-band ESR experiment more clearly distinguished the perpendicular components from the parallel component, resolving the perpendicular components into x and y components. The X-band powder spectrum was similar to the X-band ESR spectrum of the radical in a frozen solution of toluene. The computer simulation spectra performed using the obtained parameters fitted the experimental spectra well. A comparison of the amplitude of g( perpendicular)(gx, gy) with that of gz showed that the unpaired electron is delocalized over the pi-conjugated framework. Considering the hyperfine coupling constant, it was concluded that about 16% of the unpaired electron distributed over the nitrogen nucleus at the para-position. This study thus showed the significant potential of a multifrequency ESR approach to a powder sample radical in terms of its high resolution with g value.

Formation of Phenoxy and Cyclopentadienyl Radicals from the Gas-Phase Pyrolysis of Phenol

“…31 The single characteristic parameter in our case is the high g-value (2.00482-2.00500 at high microwave power, >2 mW) which is in the range of the g-values for phenoxy radicals in liquid solution (∼2.00461) and substituted phenoxy radicals (non-halogenated) in various media of ∼2.00530 (Table 1). This shift of the g-value depends significantly on the spin density of Step-by-step annihilation of initial spectrum A (g ) 2.00745) to the final phenoxy radical spectrum C (g ) 2.00582).…”

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

“…As seen in Figure 3, the simulated results successfully reproduce the experimental on the all-band of the phenoxyl radicals. 15,16 The ESR parameters obtained from the assignment of the W-band spectrum are summarized in Table 1. The orientation of the g-tensor in the radical can be defined as illustrated in a previous paper.…”

“…16 The polycrystalline samples of phenoxyl radical derivatives diluted in the corresponding phenol matrix can be prepared either by method 1; UV-irradiation of corresponding phenol matrix, 16 or by method 2; mixing corresponding primary phenol matrix with phenoxyl radical derivative generated from chemical oxidation (PbO 2 oxidation) of corresponding phenol (shown in Figure 1). 15,16 However, in these studies, the X-band ESR spectrum of a polycrystalline radical sample derived from a PbO 2 oxidation of 2,6-di-tert-butyl-4-hydroxymethylphenol in toluene solution in vacuum at room temperature showed a singular pattern, that is to say, anomalously large doublet structure. The generated compound was not evidently the corresponding radical, that is 2,6-di-tert-butyl-4-hydroxymethylphenoxyl radical, from the splitting in the X-band spectrum.…”

“…In The Journal of Physical Chemistry A, we recently reported a multi-frequency ESR study of the polycrystalline phenoxyl radical of ¡-(3,5-di-tert-butyl-4-hydroxyphenyl)-Ntert-butylnitrone in a diamagnetic matrix, 15 which is very useful as a spin-trapping technique. As reported, we successfully interpreted the powder-pattern ESR spectra and determined the ESR parameters (g-tensor and hyperfine tensor) using high-frequency ESR (Q-and W-band ESR) techniques in addition to the conventional X-band ESR.…”

“…We previously reported "Pulsed ESR study of electron spin relaxation times of polycrystalline phenoxyl radical derivative in a diamagnetic crystal" in the journal, Solid State Ionics. 17 In that study, the analysis of a temperature dependence of the electron spin relaxation times from the viewpoint of the molecular motions is correct, however, we regarded a radical generated by PbO 2 oxidation as the corresponding radical, since in the case of the other phenols, 15,16 the corresponding phenoxyl radicals can be derived by a similar way. Thus, the present paper also corresponds to the errata of the previous report.…”