A RAMAN-SPECTROSCOPIC AND DIFFERENTIAL SCANNING CALORIMETRIC STUDY OF THE DIFFERENT CRYSTALLINE PHASES OF GUAIACOL

Low-frequency (10-200 cm-1) Raman spectra of two crystalline phases of guaiacol and its deuterated analogues were recorded. The spectra of the two phases α and β are completely different in the lattice region, the lattice bands of the low-temperature α phase being shifted to higher wavenumbers. A factor-group analysis was performed, assuming that the compound crystallizes in the monoclinic space group P21/c with four molecules in the unit cell. The phase transition was studied with differential scanning calorimetry. For slowly cooled samples, two distinct endotherms were detected upon heating, a crystal-crystal transition in the temperature range 250-260 K, and a melting peak at around 303 K. Rapid cooling of liquid samples caused vitrification, and upon heating a second-order phase transition from a glassy to an amorphous state was observed at 205 K. Crystallization was found to begin at 230 K and occurred in two stages. On the basis of the lattice region spectral analysis and the DSC measurements, it seems probable that the phase transition involves both methoxyl group conformational motion and changes in hydrogen-bonding patterns. © 1990.