Electron transfer reactions and associated conformational changes: Electrochemical reduction of trans- 1,2-diiodocyclohexane

Abstract

The preparation of trans-1,2-diiodocyclohexane by reaction of cyclohexene and iodine has been characterized. Equilibrium favors the diiodide in chloroform or cyclohexene but dissociation occurs in dimethylformamide (DMF). Solutions in cyclohexene were introduced into cold DMF for study in the latter solvent. 1H and 13C NMR were used to confirm that the trans isomer is formed and to obtain relative populations of the conformers with axial iodines (aa) and equatorial iodines (ee). The ratio of concentrations of aa to ee is 4.0 in DMF at −55° C. Platinum microdisc electrodes were used to investigate the electrochemical reduction by cyclic voltammetry. At low temperatures and high scan rates in DMF solvent, the reduction peak for trans-1,2-diiodocyclohexane splits into two peaks. The peak appearing at less negative potential was assigned to the reduction of aa and the second peak to ee. Digital simulations were fit to the background-corrected voltammograms to obtain the conformational equilibrium and rate constants for temperatures in the range of 0 to −40° C.