ESR Studies of the Cation Radicals Produced by SbCl<SUB>5</SUB> Oxidation of Some Biphenyls with <I>ortho</I>- and <I>para</I>-Dialkyl Substituents

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概要

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• The cation radicals of some alkylbiphenyls such as 4,4′-bitolyl, 4,4′-di-<I>t</I>-butylbiphenyl, and 2,2′, 4,4′, 6,6′-bimesityl, were generated by SbCl<SUB>5</SUB> oxidation in CH<SUB>2</SUB>Cl<SUB>2</SUB>. The ESR observation was carried out, and the <I>Q</I>, values of the methyl and <I>t</I>-butyl were estimated based on either the theoretical spin density or the experimentally-determined spin density from the <SUP>13</SUP>C-hyperfine splitting. The <I>Q</I>, value of the methyl in the cation radical was found to be 1.5 times that for the anion radical. The <I>t</I>-butyl groups of the cation radical also showed a much larger <I>Q</I> value than that for the anion radical. The perturbation of the spin density due to the steric hindrance was investigated with reference to the prediction of the McLachlan's MO calculations carried out for the hindered biphenyl. The experimentally-determined spin density derived from the <I>Q</I> value established for the <I>para</I>-derivative can be adequately interpreted on the assumption that the planar character of the biphenyl would be much reduced, contrary to the tendency found for the anion radicals. This effect suggests that a different delocalization of the unpaired electron may be expected between the cation and the anion radical: that is, the unpaired electron brings about a fair bonding on the central 1–1′ bond in the anion radical, but an antibonding for the cation radical, because the odd π-orbital of the cation has its node between the central 1–1′ bond.

• 公益社団法人 日本化学会の論文

著者

• Suga Masao

  Department of Chemistry, Faculty of Science, Ehime University

• Ishizu Kazuhiko

  Department Of Chemistry Faculty Of Science Ehime University

• Ohuchi Muneki

  Department of Chemistry, Faculty of Science, Ehime University

• Nemoto Fujito

  Department of Chemistry, Faculty of Science, Ehime University

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