NMR spectroscopic determination of preferred conformations of quinidine and hydroquinidine.

NMR spectra of quinidine (I), hydroquinidine (II), and their respective acetyl derivatives (III and IV) were compared. The chemical shifts of some protons in I differed from those of their counterparts in II. These values were concentration dependent in I and II; they were similar in III and IV but not concentration dependent. The implications of these findings and the correlation of the NMR data with the preferred conformations are discussed.