The radical anion of [24](1,2,4,5)cyclophane

Abstract

The radical anion of [2₄](1,2,4,5)cyclophane (I) has been investigated by e.s.r. and e.n.d.o.r. spectroscopy under a variety of conditions. In dimethylformamide (counterion Et₄N⁺) and in 1,2-dimethoxyethane–hexamethylphosphoric triamide (3 : 1)(counterion K⁺) a ‘free’ or loosely associated radical anion (If^–˙) is formed (effective symmetry D_2h), whereas in tetrahydrofuran and 2-methyltetrahydrofuran (counterion K⁺ or Cs⁺) a tightly ion paired species (Ip^–˙) is present (symmetry C_2v; a_Kca. 0.1 or a_Csca. 0.6–0.8 mT). In 1,2-dimethoxyethane (counterion K⁺), at low temperatures, (If^–˙) and (Ip^–˙) give rise concurrently to distinct e.s.r. and e.n.d.o.r. spectra; the inter-conversion (If˙⁺)+ K⁺⇌(Ip˙^–)K⁺ must thus be slow on the hyperfine time-scale. The concentration ratio [(Ip^–˙)]/[(If^–˙)] in 1,2-dimethoxyethane is ca. 5 at 178 K and increases upon raising the temperature.