Spectroscopic studies of conformational polymorphism in 4-methylphenol

In this work, conformational polymorphism in 4-methylphenol has been studied using a Fourier-transform infrared (FTIR) spectroscopy. The first time we have received the FTIR spectra of the stable and two metastable phases of 4-methylphenol and their temperature dependencies at temperatures from 300 to 12 K in the spectral region of the methyl group (CH3) deformation vibrations. Analysis of the FTIR spectra showed that there are significant differences in the position and shape of the bands related to the deformation bending β(CH3) and rocking ω(CH3) vibrations when passing from one polymorph to another. A particular feature of the methyl group in the 4-methylphenol molecule is that it does not take part in hydrogen bonding interaction. This made it possible to relate the observed changes in the FTIR spectra with changes in the geometrical parameters of the 4-methylphenol molecule. This in turn allowed us to conclude that the polymorphs under study consist of different conformers of 4-methylphenol molecule.