Spectroscopic study of phase polymorphism and vibrational assignments for 2,2-dinitropropane

The infrared spectra between 3800 and 15 cm−1 of (CH3)2C(NO2)2 and (CD3)2C(NO2)2 as a function of temperature are recorded. All the phases known from the calorimetric study are obtained. The Raman spectra of both the compounds are also recorded for the liquid and plastic phases and for the crystalline phase in the lattice vibration region. The assignments of the observed bands are proposed on the basis of the isotopic shifts and the Raman polarization data. The changes in the spectra observed in the phase transitions are compatible with the phase transition mechanism proposed on the basis of the calorimetric study and additionally indicate that the phase III → → phase II transition is connected with the change of the NO2 group configuration in the molecule.