Variable temperature (100-360 K) single-crystal X-ray diffraction study of the orthorhombic polymorph of paracetamol (p-hydroxyacetanilide)

The crystal structure of the orthorhombic polymorph of paracetamol was refined in Pbca space group by single-crystal X-ray diffraction at 100, 200, 300, 360 K. Cell parameters were measured in the range between 100 and 360 K. The anisotropy of lattice strain on cooling was analysed and compared with that induced by increasing pressure. The data for the ortborhombic paracetamol were compared also with the results previously reported for the monochnic form of the same compound. The bulk thermal expansion coefficient of the orthorhombic polymorph is larger than that for the monoclinic form. Maximum compression on cooling was observed in the direction normal to the molecular layers. The structure expanded slightly on cooling in the crystallographic a-direction. Relative compressibility of (OHO)-O-... and (NHO)-O-... intermolecular hydrogen bonds on cooling, as well as the changes in the intramolecular geometry of paracetamol molecules and the atomic displacement parameters were measured and analysed.