Studies on vitamin D and related compounds III. Short communication on the cis‐trans isomerization of calciferol and the properties of “trans”‐vitamin D2

Isomerization of vitamin D2 in apolar solvents at room temperature under the influence of small amounts of iodine in diffuse daylight yields a compound that could be isolated in the form of the crystalline phenylazobenzoate. Spectra of solutions of the free vitamin D isomer obtained upon saponification of the ester are presented. They support the view that the isomer should be considered as trans‐vitamin D2 having structure A (fig. 3).