Extensive hydrogen and halogen bonding, and absence of intramolecular hydrogen bonding between alcohol and nitro groups in a series of endo-nitronorbornanol compounds

The influence of the substituent at the C2 position on the hydrogen-bonding patterns is compared for a series of five related compounds, namely (±)-3-exo,6-exo-dibromo-5-endo-hydroxy-3-endo-nitrobicyclo[2.2.1] heptane-2-exo-carbonitrile, C ₈H ₈Br ₂N ₂O ₃, (II), (±)-3-exo,6-exo-dibromo-6-endo-nitro-5- exo-phenylbicyclo-[2.2.1]heptan-2-endo-ol, C ₁₃H ₁₃Br ₂NO ₃, (III), (±)-methyl 3-exo,6-exo-dibromo-5-endo- hydroxy-3-endo-nitrobicyclo[2.2.1]heptane-2-exo-carboxylate.0, C ₉H ₁₁Br ₂NO ₅, (IV), (±)-methyl 3-exo,6-exo-dibromo-7-diphenylmethylidene-5-endo-hydroxy-3-endo-nitrobicyclo[2. 2.1]heptane-2-exo-carboxylate, C ₂₂H ₁₉Br ₂NO ₅, (V), and (±)-methyl 3-exo,6-exo-dibromo-5-endo-hydroxy-3- endo-nitro-7-oxabicyclo[2.2.1]hep-tane-2-exo-carboxylate, C ₈H ₉Br ₂NO ₆, (VI). The hydrogen-bonding motif in all five compounds is a chain, formed by O - H⋯O hydrogen bonds in (III), (IV), (V) and (VI), and by O - H⋯N hydrogen bonds in (II). All compounds except (III) contain a number of Br⋯Br and Br⋯O halogen bonds that connect the chains to each other to form two-dimensional sheets or three-dimensional networks. None of the compounds features intramolecular hydrogen bonding between the alcohol and nitro functional groups, as was found in the related compound (±)-methyl 3-exo,6-exo-dichloro-5-endo-hydroxy-3- endo-nitrobicyclo[2.2.1]heptane-2-exo-carboxylate, (I) [Boeyens, Denner & Michael (1984b). J. Chem. Soc. Perkin Trans. 2, pp. 767-770]. The crystal structure of (V) exhibits whole-molecule disorder.