CIS-trans isomerization of nitrostilbenes in the presence of aromatic amines

Voltammetric studies of the reduction of cis- and trans-α-nitrostilbene

“…This, of course, is much lower than the barrier for isomerization of the neutral olefin. The lowering of the isomerization barrier on going from the neutral compound to the radical anion can be explained qualitatively by the reduction of the double-bond character of the olefinic bond, thus lowering the activation energy for isomerization [16]. The lowering of the doublebond character is indicated in the calculations (DFT) by a lengthening of the bond from 1.349 A in neutral cis-1 to 1.401 A in its radical anion.…”

“…The trans-to-cis isomerization can be effected by electron transfer [14] or formation of charge-transfer complexes with aromatic amines [16]. Electron transfer to the a-nitrostilbenes leads to rapid dimerization so isomerization could not be detected [5]; but, in the charge-transfer complex with aniline, more than half of cis-1 was converted to trans-1 implying that the two isomers have almost exactly the same Gibbs energy, at least within the charge-transfer complex [16].…”