Cis/trans-isomerizations in 1,2-bis(2-thienyl)ethene derivatives: A joint experimental and computational approach

Article abstract of DOI:10.1016/S0022-2860(99)00180-5

Two substituted 1,2-bis(2-thienyl)ethenes were synthesized and their Z/E-isomerization was studied in solution. Despite their structural similarities, they behaved very differently concerning the position of the equilibrium and the rate with which it was established: 1,2-bis(3-methoxy-2- thienyl)ethene (BMTE) was found to exist completely in the E-form and the transformation from Z to E was extremely fast, while 1-cyano-1-(2-thienyl)-2- (3-methoxy-2-thienyl)ethene (CTMTE) displayed an equilibrium mixture composed of 97% Z- and 3% E-CTMTE, which was reached far slower. In an attempt to rationalize these differences ab initio calculations were performed which enabled us to correlate relative energy differences of starting and end conformations and of estimated intermediary states on the one hand with the experimentally observed isomerizational behaviour on the other. Furthermore, the data present insight into the effects of the methoxy and nitrile group on E/Z stability and conjugation length.