The Radical Anions of Some Substituted [2.2]Paracyclophanes

The radical anions of the following substituted [2.2]paracyclophanes have been characterized by ESR. and ENDOR. spectroscopy: 4, 16-dicyano- ( o - 2 ), 4, 12-dicyano- ( p - 2 ), 4,5,12,13-tetracyano- ( 3 ) and 4,5,12,13-tetrakis (alkoxycarbonyl)- [2.2]paracyclophanes ( 4-R , where R = Me, Et, iPr or tBu is the ester alkyl group); 4,5-bis(methoxycarbonyl)[2.2]paracyclophane-12, 13-dicarboxylic anhydride ( 5 ); [2.2]paracyclophane-4,5:12, 13-tetracarboxylic bisanhydride ( 6 ) and bisimides ( 7-R , where R = H, D, Me or Ph is the substituent at the imide N-atom). Comparison of the hyperfine data for these radical anions with those for analogously substituted derivatives of benzene indicates that the most prominent coupling constants are approximately halved on passing from the latter to the former. Lowering of the symmetry, as a consequence of ion pairing, has been observed for the radical anions 4- i Pr documentclass{article}pagestyle{empty}begin{document}$^{ominus atop dot{}}$end{document} and 4- t Bu documentclass{article}pagestyle{empty}begin{document}$^{ominus atop dot{}}$end{document} associated with the counterion K ⊕ in 1,2-dimethoxyethane at 183 K, but not for 4-Me documentclass{article}pagestyle{empty}begin{document}$^{ominus atop dot{}}$end{document} and 4-Et documentclass{article}pagestyle{empty}begin{document}$^{ominus atop dot{}}$end{document} under the same conditions. This result suggests that the migration of K ⊕ between the preferred sited in two equivalent ion pairs is slowed down by the steric hindrance arising from the bulky iPr and tBu ester groups.