The radical ions of 4,5,7,8-tetramethyl[2.2]paracyclophane

Abstract

By the use of strong oxidising and reducing agents, 4,5,7,8-tetramethyl[2.2]paracyclophane (II) has been converted to its radical cation (II⁺˙) and to its radical anion (II^–˙). These radical ions, as well as those generated from the 12,13,15,16-tetradeuterio ([²H₄]II) and the 1,1,10,10,12,13,15,16-octadeuterio-derivative ([²H₈]II), have been studied by e.s.r. and, in part, by e.n.d.o.r. spectroscopy. In (II⁺˙), the bulk of the spin population is located on the methyl-substituted benzene ring, whereas, in (II^–˙), it is found on the ring bare of methyl groups. This result corresponds to the effect of the alkyl substitution which enhances the donor and weakens the acceptor character of a π-system. Comparison of the hyperfine data for (II˙⁺) with those of the dimeric radical cation (II₂⁺˙) reveals considerable deviations from the ratio of ca. 0.5, expected for the coupling constants of the protons in such two species. In the e.s.r. spectra of (II^–˙) the large splittings from the nuclei of the counterions (³⁹K 0.102 and ¹³³Cs 0.596 mT) are notable; they exceed by one order of magnitude the corresponding values for the radical anion of [2.2]paracyclophane (I).