Geometrical inversion in light

Abstract

One of the most interesting types of photochemical change is exhibited by the class of organic compounds known as geometrical isomers. Under the influence of ultra-violet radiation these substances change from the cis-form to the trans-form and vice versa . Although many compounds of this class are known, no quantitative investigation has been made of the relation between the light energy absorbed and the amount of change produced except in the case of maleic and fumaric acids. This pair of geometrical isomers was investigated by Warburg, who found a very low quantum efficiency for the change in both directions. Yolmar, however, stated that maleic-fumaric acids and citraconic-mesaconic acids underwent a decomposition of the same nature as oxalic and malonic acids, where carbon dioxide is one of the products of decomposition.