Phase Transitions In Bicyclic Compounds

Abstract

Abstract The study of a wide variety of organic structures by differential scanning calorimetry reveals that bicyclic caged compounds frequently possess a pre-melting phase transition. These compounds are characterized by low entropies of fusion (less than 21 j/K, mole) and relatively large entropies of transition. Derivative structures have been investigated and it has been found that substituents such as the anhydride, nitrile, and carbonyl groups retain the polymorphic phase properties of the parent ring systems while groups such as the imide, methylimide, and carboxylic acid exclude the appearance of a disordered solid phase. The phase properties of chloro and hydroxyl derivatives investigated are more varied and depend on the position of these groups on the ring. The variety of compounds studied shows that hysteresis is a common occurrence in all of these ring systems.