Conformational Changes of an N,N'-Dimethyl-Substituted Dithionoamido-18- Crown-16 Macrocycle
BRIGHAM YOUNG UNIV PROVO UT DEPT OF CHEMISTRY
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Dithionoamide ligand 8 exhibited a time-dependent optical rotation. The first measurement was taken after two minutes of dissolution of the crystals recrystallized from ethanol. The optical rotation of this solution increased gradually and after 30 min. it was 106.0 degrees, after 40 min. 110.4 degrees, after 60 min. 112.2 degrees and after 90 min. 112.3 degrees. The optical rotation of the solution was then checked daily for 2 weeks, but no additional changes were observed. When 8 was recovered from the chloroform solution and recrystallized from ethanol, the resulting crystalline 8 had the same optical rotation and mp as the original solid. As early as 2 min. after dissolving the crystals, new peaks appeared which can be attributed to a second, less symmetrical conformer. After 40 min about the time equilibrium was established the H NMR spectrum indicated the presence of a third conformer as well.
- Physical Chemistry