Magnetoelectrochemistry of 4,4′-bis(dimethylamino)biphenyl and 4,4′-dinitrobiphenyl azacrown macrocyclic lactams

The voltammetric behaviour at carbon fibre microelectrodes under the application of static magnetic fields of two series of macrolactams containing in their structure 4,4′-bis(dimethylamino)biphenyl or 4,4′-dinitrobiphenyl groups in MeCN solution is described. The response of 4,4′-dinitrobiphenyl receptors is dominated by two successive one-electron reduction processes at −0.9 and −1.6 V versus AgCl/Ag. 4,4′-bis(dimethylamino)biphenyl-containing receptors display two one-electron oxidations above +0.8 and +1.0 V. In both cases, a dihedral/planar interconversion precedes the second electron transfer step. Upon application of moderate (0.05–0.2 T) static magnetic fields to the electrochemical cell, the rate of such dihedral/planar interconversion is lowered for both the reduction of 4,4′-dinitrobiphenyl receptors and the oxidation of 4,4′-bis(dimethylamino)biphenyl lactams. The electrochemical response of N-methylated receptors, for which different cisoid–cisoid, cisoid–transoid, and transoid–transoid forms exist, exhibits a significant peak splitting that can be associated to the presence of such conformational isomers. Application of magnetic fields produces a relative enhancement of some peaks that can be interpreted in terms of differential magnetoconvection involving such conformational isomers.