Abstract In this work we show that the two known polymorphs of 4′-hydroxyacetophenone (form I, monoclinic, P21/c, Z′/Z=1/4; form II, orthorhombic, P212121, Z′/Z=2/8) can be clearly distinguished by diffuse reflectance infrared Fourier-transform infrared (DRIFT) spectroscopy. The experimental studies were complemented by density functional theory calculations (DFT) carried out at the B3LYP/cc-pVTZ level of theory on the E and Z molecular conformers present in the solid forms I and II, respectively. Comparison between the calculated and experimental spectra allowed understanding the influence of polymorphism on the main intermolecular interactions. It was concluded that the differences in the hydrogen bond (H-bond) patterns of the two forms previously highlighted by X-ray diffraction were also captured by the vibrational spectra. Finally, attenuated total reflectance (ATR) spectra suggested that there is a direct connection between the predominant solvent-induced molecular conformation of 4′-hydroxyacetophenone (E or Z) and the selective nucleation of form I from water and form II from ethanol.