A new form of resorcinol. II. Thermodynamic properties in relation to structure

Abstract

As is discussed below, resorcinol is one of a limited number of substances for which the denser polymorph is stable at higher temperatures. It is also one of the limited number of substances for which the detailed structure has been worked out for both forms. The correlation of thermodynamic properties wit structure is thus of particular interest, and is discussed in the first part of this paper. This discussion is followed by a description of experiments on the heat of transition between the two polymorphs, on the specific volume of liquid resorcinol, and on the relative stabilities of α- and β -resorcinol in the compounds C 6 H 4 (OH) 2 and C 6 H 4 (OD) 2 . Brief reference is also made to experiments on the polymorphism of penta-erythritol. The relation between enantiotropy and structure in resorcinol When two polymorphs can exist in thermodynamic equilibrium, it becomes possible to correlate the statistical and metrical factors which determine crystal structure. The most compact formulation of the statistical factors is obtained by using the thermodynamic function of the solid. By definition, the free energy G 1 of a solid may be written G 1 = H 1 – TS 1 , where H 1 is the heat content and S 1 the entropy of the solid