The thermal behavior of 3-benzoylpropionic acid (BPA) was investigated using single-crystal and synchrotron powder X-diffraction, as well as differential scanning calorimetry analysis. The study revealed the existence of two subtly distinct structures of BPA, with different numbers of molecules in the asymmetric unit. A detailed analysis of conformational changes in the molecules, supported by quantum mechanical calculations, allowed for an explanation of the origins of the two phases. The continuous transition upon cooling is linked to the emergence of pseudosymmetry. The transition mechanism was revealed by thermal expansion analysis. Furthermore, the research provided evidence to refute the previously reported premise of BPA's colossal thermal expansivity.

3-Benzoylpropionic acid undergoes continuous transition associated with pseudosymmetry melting upon heating. The transition stems from a directional steric crowding, which refutes the recent premise of its colossal thermal expansion.