Wöhler and Liebig Revisited: 176 Years of Polymorphism in Benzamide - and the Story Still Continues!

In 1832, Friedrich Wöhler and Justus von Liebig described the existence of polymorphism in molecular crystals for the first time in the case of benzamide. 175 years later, the crystal structure of this historical polymorph could be finally solved. Surprising similarities regarding the packing motifs between all three known forms can be found. According to Ostwald’s rule, high supersaturations are needed to crystallize the most unstable Form II from solution. Herein we present a way in which all three known forms for benzamide can be concomitantly crystallized out of solution. With this trimorphic mixture at hand, a more detailed stability test could be performed and further characterization applying solid-state NMR-, Raman, and IR-spectroscopy was possible.