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[R,S]-Ethambutol dihydrochloride: variable-temperature studies of a dimorphic system with very similar packing
Janice M Rubin-Preminger1, Joel Bernstein, Robin K Harris
1Department of Chemistry, Ben-Gurion University of the Negev, P.O. Box 635, Be'er Sheva, Israel, 84105.
Abstract:
The two polymorphs (Forms I and II) of [R,S]-ethambutol dihydrochloride transform enantiotropically and reversibly in a single-crystal-to-single-crystal phase transformation mode. These structurally very similar forms have been characterized and their thermodynamic relationship has been investigated by variable-temperature solid-state carbon-13 nuclear magnetic resonance, variable-temperature powder X-ray diffraction, differential scanning calorimetry, and optical microscopy. The nuclear magnetic resonance results are compared with those for the two polymorphs of the [S,S] diastereomer with known structures.
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