Isomerization of the Cubane Radical Cation to the Bridged 1,4-Bishomobenzene(Bicyclo3.3.0octa-2,6-diene-4,8-diyl) Radical Cation

摘要

The electronic structure and the interconversion of the radical cations of the(CH)8 group have recently attracted attention. Among the (CH)8 hydrocarbons, cubane has high symmetry and the highest strain energy. Its physicochemical properties continue to attract experimental and theoretical interest. The cubane radical cation (1) was first studied in neon matrices at 4K. The observed nonet EPR spectrum was explained by invoking a dynamic Jahn-Teller distortion of 1. Because of the narrow temperature range of neon matrices, further reactions of 1 were not observed. Here we report isomerization of 1 to the bridged 1,4-bishomobenzene radical cation (2), which was first demonstrated to be formed by the ring-opening of the semibullvalene radical cation. A mechanism of this novel thermal rearrangement is suggested. Another highly strained compound in the (CH)8 hydrocarbon family is cuneane. We show here that radiolytic oxidation of cuneane also yields. 1 was generated by the radiolytic oxidation of cubane in three Freon matrices (CFC3, CF3CC3, and CF2CiCFCl2). Similar spectra of 1 were obtained in all three matrices. The broader EPR line width observed is attributable to the weak interaction of the unpaired spin with chlorine or fluorine atoms of Freon molecules observed in many other systems.