Photochemical and thermal isomerizations of cis- and trans-cinnamic acids, and their photostationary state

Abstract

Cis-Cinnamic acid was prepared photochemically from the trans isomer according to a published method, but was isolated by vacuum distillation. The photostationary state of these acids has been determined for moderately concentrated solutions of each isomer exposed to unfiltered ultraviolet. The position of the cis–trans thermal equilibrium approached from all cis- and from all trans-isomers has been tested without solvent and found to lie at, or very close to, 100% trans. Kinetic examination of the rates of these isomerizations shows that they fit a kinetic expression of the form −d[cis]/dt = k[cis] [H⁺].