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DuP 747, a selective kappa agonist analgesic, was found to have at least two polymorphic forms, and this was confirmed by X-ray powder diffraction. DSC and thermomicroscopic studies indicated the polymorphic pair to be monotropic. Solubility studies suggested the relative stability of the two forms to be similar. The infrared (IR) and Raman spectra of the two crystal forms were significantly different, and their complementary nature was shown from the differences in peak intensities. Solid-state 13C-NMR data of the polymorphs showed only minor differences between the two forms. When viewed on the molecular level through the use of vibrational and NMR spectroscopies, the conformation of the molecule in the two polymorphs appears to be roughly equivalent. The magnitude of the spectral differences of the two polymorphs is, however, consistent with those that can be expected for two crystal forms that have resulted from different modes of packing, as caused by the solvent environment.

Losartan, an antihypertensive agent in clinical development, was found to exist in two enantiotropic polymorphic forms, a low-temperature stable form (Form I) and a high-temperature stable form (Form II), the temperatures at which they are stable being related to the transition temperature. X-ray powder diffraction patterns indicated differences in the crystal packing of the two forms. The vibrational data from infrared and Raman spectroscopy suggested a subtle change in molecular conformation and crystal packing in the two forms. Solid-state 13C NMR data of the polymorphs concurred with the vibrational data and indicated that, while the observed line widths reflect no major changes in crystallinity, signal multiplicities and chemical shifts do reflect differences in molecular packing in the respective unit cells. Thus, in the absence of crystallographic data, useful structural information could be derived from spectroscopic results to identify each of the crystalline forms.

C(60) and liquid bromine react to form C(60)Br(24), a crystalline compound isolated as a bromine solvate, C(60)Br(24)(Br(2))(x), The x-ray crystal structure defines a new pattern of addition to the carbon skeleton that imparts a rare high symmetry. The parent C(60) framework is recognizable in C(60)Br(24), but sp(3) carbons at sites of bromination distort the surface, affecting conformations of all of the hexagonal and pentagonal rings. Twenty-four bromine atoms envelop the carbon core, shielding the 18 remaining double bonds from addition. At 150 degrees to 200 degrees C there is effectively quantitative reversion of C(60)Br(24) to C(60) and Br(2).