Another orthorhombic crystal modification of n-hexatriacontane and its vibrational spectra

n-Hexatriacontane has been found to crystallize into a new type of orthorhombic form with the unit cell dimensions of a=7.40 Å, b=5.58 Å, and c=84.6 Å, quite different from the ordinary orthorhombic lattice. On the basis of the crystallographic as well as the spectroscopic evidence, it has been concluded that one repeat distance along the c direction contains two monomolecular layers, each assuming essentially the same structure as that of the ordinary (011) monoclinic modification. Contrary to the monoclinic form, the successive layers turn alternately through 180° about an axis normal to the ab plane. The possible space group has been found to be Pbcn-D¹⁴_2h or Pbca-D¹⁵_2h. The crystal structure presented here corresponds to an extreme case in polytypism found in crystal growth of the monoclinic lattice. The infrared absorptions due to the terminal methyl groups and the low-frequency Raman spectra of the present orthorhombic form differ from those of the monoclinic one, reflecting difference in the interfacial structure between these two modifications.