Relative configuration, absolute configuration and absolute structure of three isomeric 8-benzyl-2-[(4-bromo­phenyl)(hy­droxy)methyl]-8-aza­bicyclo­[3.2.1]octan-3-ones

The title compounds, C₂₁H₂₂BrNO₂, are isomeric 8-benzyl-2-[(4-bromo­phenyl)(hy­droxy)methyl]-8-aza­bicyclo­[3.2.1]octan-3-ones. Compound (I), the (±)-exo,syn-(1RS,2SR,5SR,9SR) isomer, crystallizes in the hexa­gonal space group R, while compounds (II) [the (+)-exo,anti-(1R,2S,5S,9R) isomer] and (III) [the (±)-exo,anti-(1RS,2SR,5SR,9RS) isomer] crystallize in the ortho­rhom­bic space groups P2₁2₁2₁ and Pna2₁, respectively. The absolute configuration was determined for enantio­merically pure (II). For the noncentrosymmetric crystal of (III), its absolute structure was established. In the crystal structures of (I) and (II), an intra­molecular hydrogen bond is formed between the hy­droxy group and the heterocyclic N atom. In the crystal structure of racemic (III), hydrogen-bonded chains of mol­ecules are formed via inter­molecular O—H...O inter­actions. Additionally, face-to-edge π–π inter­actions are present in the crystal structures of (I) and (II). In all three structures, the piperidinone rings adopt chair conformations and the N-benzyl substituents occupy the equatorial positions.