Abstract
Crystalline (−)-scopolamine hydrohalide (bromide and chloride) salts exist in two conformational families for the tropate ester moiety: the compact conformation (hydrates, phenyl ring underneath the scopine moiety), and the extended conformation (anhydrates, phenyl ring ca. antiperiplanar to oxiranyl O-atom). CPMAS 13C NMR solid-state spectra of anhydrates and hydrates are different. In both tertiary and quaternary scopolammonium salts, phenyl rings are immobile in compact conformation crystals having ca. 2.5 A close lateral neighbors on both faces of the planar moiety. Phenyl rings undergo a π-flip in extended conformation crystals having ca. 3.0 A close lateral neighbors on either face of the aromatic plane. Due to different OC−Cα−CH2OH dihedral angles [synperiplanar (eclipsed, in compact) and (+)-synclinal (gauche, in extended)], the methylol carbon chemical shifts of crystalline tertiary and quaternary scopolammonium salts and analogues are diagnostic markers for the tropate ester solid-state conform...
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