Hyposantonin and isohyposantonin do not undergo conversion such as that seen with desmotroposantonin by treatment with sulfuric acid, but yield dihydrosantinic acid. Those two compounds also undergo racemization by alkali fusion and yield optically inactive dihydrosantinic acid. It is assumed from the formation of dihydrosantinic acid that the steric difference between hypo- and isohypo-santonin is the difference in the position of the hydrogen atom attached to C₅. Crystallographic measurements were made of optically active and inactive dihydrosantinic acids.