| Abstract: | The X-ray structure of 15-apoviolaxanth-15-al ( = (1′S,2′R,4′S,2E,4E,6E,8E)-9-(1′,2′-epoxy-4′-hydroxy-2′,6′,6′-trimethylcyclohexyl)-3,7-dimethylnona-2,4,6,8-tetraenal) is reported. The four symmetry-independent molecules in the asymmetric unit are linked into X-shaped spirals by intermolecular H-bonds. Additional H-bonds interconnect the spirals, forming wave-like chains. The geometry of the polyene side chain possesses the same in-plane bending observed for related retinal and carotenoid compounds. The polyene side chain deviates from planarity by twists of up to 10° about each bond; some of the largest twists are about C?C bonds. The epoxycyclohexane ring possesses a distorted ‘C(3)-sofa’ conformation. The torsion angles about the bond connecting the polyene chain to the cyclohexane ring are compared with equivalent torsion angles in molecules containing epoxide rings substituted with a π-system in order to examine possible interactions between the epoxide group and the π-system, either through pseudoconjugation, or through an interaction of the nonbonding orbitals of the epoxy O-atom with the π-orbitals of the polyene chain. The latter is considered to be more likely. |
