Monoclinic and orthorhombic polymorphs of paracetamol-solid state linear dichroic infrared spectral analysis

Solid-state linear dichroic infrared (IR-LD) spectral analysis of both monoclinic (form I) and orthorhombic (form II) polymorphs of paracetamol was carried out using an orientation technique as a nematic liquid crystal suspension. The so-called reducing-difference procedure for polarized spectra interpretation was applied and the obtained supramolecular stereo structural data of both modifications were compared with known crystallographic ones. A detailed vibration assignment of characteristic frequencies of forms I and II was also applied. A quantitative FT-IR spectral approach for monoclinic form determination in mixtures by the intensity ratio of 1610 cm−1 peak (characteristic for both forms) to 1666 cm−1 one (attributed to orthorhombic modification) was presented, as well.