Iodine-Catalyzed Thermal cis-trans Isomerization of Stilbene

The iodine-catalyzed thermal cis → trans conversion of stilbene has been studied kinetically in n-hexane in temperature range 62.0∼68.8°C. The reaction rate obtained spectrophotometrically has been found to be proportional to the concentration of cis-stilbene and to the square root of iodine concentration. The overall activation energy has been found to be 25 kcal./mol. The results have been interpreted in terms of the thermal dissociation of iodine molecules followed by the formation of a transient complex between cis-stilbene and atomic iodine.