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    An electron paramagnetic resonance and density-functional theory study on the methyl isotropic hyperfine coupling constants in gamma-irradiated 2,6-di-tert-butyl-4-methylphenol
    (TAYLOR & FRANCIS LTD, 2013) Turkkan, Ercan; Dereli, Omer; Sayin, Ulku; Tapramaz, Recep
    Single crystal of gammairradiated 2,6-di-tert-butyl-4-methylphenol (BHT) was investigated using an electron paramagnetic resonance (EPR) technique at different orientations in the magnetic field at room temperatures. Taking into consideration the chemical structure and the experimental spectra of the irradiated single crystal of BHT, we assumed that one phenoxyltype paramagnetic species was produced having an unpaired electron localized at the methyl fragment side of the phenyl ring. Depending on this assumption, one possible radical was modeled using the B3LYP/6-311+G(d) level of density-functional theory. EPR parameters were calculated for these modeled radical using the B3LYP/TZVP and B3LYP/EPR-III level. The averaged value of isotropic hydrogen hyperfine coupling constants of rotating methyl functional group of phenoxyl radical is calculated for the first time. Theoretically calculated values of the modeled radical are in reasonably good agreement with the experimental data determined from the spectra (differences in averaged coupling constant values smaller than 5%, and differences in isotropic g values fall into 1ppt).
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    Experimental and Theoretical Electron Paramagnetic Resonance (EPR) Study on the Temperature-Dependent Structural Changes of Methylsulfanylmethane
    (MDPI, 2011) Tapramaz, Recep; Turkkan, Ercan; Dereli, Omer
    Methylsulfonylmethane (or dimethyl sulfone), a naturally produced and vitally important organosulfur compound in living organisms, was irradiated with gamma rays, and the produced radicals were investigated using electron paramagnetic resonance spectroscopy at different temperatures. The structure and behavior of the radical changed when the temperatures varied. The hyperfine splitting of the CH3 group was small, and the S-33 splitting was relatively high between 80 and -50 degrees C. When the temperature was between -50 and -160 degrees C, the S-33 splitting became small and the CH3 splitting was higher. However, the group kept rotating; therefore, only the isotropic splitting values were measured, and the g-values were anisotropic. When the temperature decreased below -180 degrees C, the CH3 group stopped rotating, and the hydrogen splitting values became nonequivalent due to an inhomogeneous electron distribution. The observed structures can be explained by referring to both the experimental and theoretically calculated values reported.
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    İzonitrosoasetofenon ve Fenilglioksim Tek Kristallerinde Tuzaklanmış İminoksi Radikallerinin Elektron Spin Rezonansı
    (Selçuk Üniversitesi Fen Edebiyat Fakültesi, 2000) Özmen, Ayhan; Tapramaz, Recep; Köksal, Fevzi; Yüksel, Hüseyin
    The Electron Spin Resonance(ESR) of iminoxy radicals trapped in gamma-irradiated isonitroseacetophenone and phenylglioxime single crystals have been studied. It has been understood that iminoxy radicals trapped in these crystals is isomeric iminoxy radicals. In addition site splitings have been observed for both of crystals for every radicals, principal components of the g and hyperfine tensors of 14N and proton; distribution spin density of unpaired electron in radicals; s and p charecters of spin density on the nitrogen, and CNO bond angle have been calculated.