Toward an Understanding of the Ambiguous Electron Paramagnetic Resonance Spectra of the Iminoxy Radical from o-Fluorobenzaldehyde Oxime: Density Functional Theory and ab Initio Studies

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• 作者：Maciej Witwicki ; Julia Jezierska
• 刊名：Journal of Physical Chemistry A
• 出版年：2015
• 出版时间：August 27, 2015
• 年：2015
• 卷：119
• 期：34
• 页码：9109-9120
• 全文大小：515K
• ISSN：1520-5215

文摘

Iminoxy radicals (R₁R₂C鈺怤鈥擮^{鈥?/sup>) possess an inherent ability to exist as E and Z isomers. Although isotropic hyperfine couplings for the species with R₁ = H allow one to distinguish between E and Z, unequivocal assignment of the parameters observed in the EPR spectra of the radicals without the hydrogen atom at the azomethine carbon to the right isomer is not a simple task. The iminoxyl derived from o-fluoroacetophenone oxime (R₁ = CH₃ and R₂ = o-FC₆H₅) appears to be a case in point. Moreover, for its two isomers the rotation of the o-FC₆H₅ group brings into existence the syn and anti conformers, depending on the mutual orientation of the F atom and C鈺怤鈥擮鈥?/sup> group, making a description of hyperfine couplings to structure even more challenging. To accomplish this, a vast array of theoretical methods (DFT, OO-SCS-MP2, QCISD) was used to calculate the isotropic hyperfine couplings. The comparison between experimental and theoretical values revealed that the E isomer is the dominant radical form, for which a fast interconversion between anti and syn conformers is expected. In addition, the origin of the significant A_F increase with solvent polarity was analyzed.}