Polymorphism in 4-Methoxy-3-nitrobenzaldehyde

Two of the three earlier reported polymorphic forms of 4-methoxy-3-nitrobenzaldehyde have been reinvestigated and fully characterized by a variety of methods including variable temperature powder X-ray diffraction, vibrational spectroscopy (infrared and Raman), calorimetry (differential scanning calorimetry, DSC), and optical microscopy. Differences of DSC thermograms, which were carried out with different cooling rates, suggest a thermodynamic/kinetic competition in the crystallization from the melt. The crystal structures of these two forms have been solved, one by single-crystal methods and the second from synchrotron powder diffraction.