Paracetamol and phenacetin (commercial samples, Kursk Drug Plant) were purified by recrystallization from an
ethanol solution. The orthorhombic modification of paracetamol was obtained from a melt according to the procedure
described in [15].
IR spectra were recorded on a Bomem MB-102 Fourier spectrometer (resolution 4 cm–1) for KBr pellets (2 mg
sample with 500 mg KBr) and solutions (at first, the spectrum of the solvent was recorded and then the spectrum of the
solution was measured in the same cell with subsequent subtraction of the spectrum of the solvent). The solvents used include
chloroform, deuterochloroform, and dimethylsulfoxide. Saturated solutions of paracetamol and phenacetin were prepared,
then their IR spectra were recorded and processed, and the solutions were successively diluted until the spectrum of the solute
completely vanished. Attempts were made to monitor the intermolecular interactions in solutions according to changes in the
spectra. As paracetamol has much lower solubility in chloroform and deuterochloroform compared to phenacetin, for
spectrum measurements in solution we used a NaCl cell 1.0 mm thick for paracetamol and a KBr cell 0.3 mm thick for
phenacetin. In each case, the spectrum of the solvent in a cell of appropriate thickness was subtracted.
For spectrum measurements in the near IR range (4000 cm–1 -10000 cm–1), an Interspec 2010 Fourier spectrometer
was used. Diffuse scattering spectra of paracetamol and phenacetin powders were recorded, which were subsequently
converted into absorption spectra.
Ab initio calculation of equilibrium geometry and normal vibration frequencies for paracetamol and phenacetin
molecules was carried out using the Gaussian-94/DFT program.