Electron-Transfer Reactions and Associated Conformational Changes. Electrochemical Reduction of Some Vicinal Dibromides

Article abstract of DOI:10.1021/ja00344a010

The effect of molecular conformation on the electrochemical reduction of derivatives of trans-1,2-dibromocyclohexane (1-4) and substituted 1,2-dibromoethanes (5-8) has been investigated by low-temperature cyclic voltammetry.Reduction via conformations with antiperiplanar bromine atoms is preffered and conformational interconversion prior to electron transfer was observed in trans-1,2-dibromocyclohexane (1), 1,1-dimethyl-trans-3,4-dibromocyclohexane (2), meso- and dl-1,2-dibromo-1,2-diphenylethane (meso-5 and dl-5), and 2,3-dibromo-2,3-dimethylbutane (8).Digital simulation of the low-temperature voltammetric data has provided thermodynamic and kinetic information on the conformational interconversion in 1, 2, 5, and 8.The energy barriers to conformational interconversion in meso- and dl-2,3-dibromobutane (meso-6 and dl-6) are quite small, and conformational effects in the electrochemical reduction of 6 could not be detected at temperatures as low as -135 deg C. 1-Methyl-cis-3,trans-4-dibromocyclohexane (3), 1-methyl-trans-3,cis-4-dibromocyclohexane (4), and meso- and dl-3,4-dibromo-2,5-dimethylhexane (meso-7 and dl-7) exist almost entirely in a single conformation.Voltammetric peak potentials of 3,4,meso-7, and dl-7 reflect the geometry of their principal conformation.