Rotating Ring‐Disk Electrodes: V . Isomerization and Reductive Coupling of Dialkyl Maleates

Abstract

The rates of isomerization and coupling of the radical anions produced on electroreduction of several dialkyl maleates [methyl (DMM), ethyl (DEM), n‐butyl (DBM)] in N,N‐dimethylformamide solutions were investigated at the rotating ring‐disk electrode (RRDE). Digital simulation methods were employed to obtain appropriate working curves and techniques were established to obtain both the first order isomerization constant and the second order dimerization constant from collection efficiency measurements. The measured values; DMM, 2.2; DEM, 6.0; and DBM, 6.7 (sec−1) show an increasing isomerization rate with increasing size of alkyl substituent (R). The coupling rates decrease with increasing ; the values are: . Comparison of these results to previous measurements of the coupling rates of the corresponding trans‐species (i.e., fumarates) indicate that the cis‐radical anions couple about two thousand times faster than do the trans.