Crystal structure of 1-(4-hydroxybenzoyl)-2,7-dimethoxynaphthalene: Contribution of classical and non-classical hydrogen bonding interactions to the molecular packing structure

Abstract

Crystal structure of 1-(4-hydroxybenzoyl)-2,7-dimethoxynaphthalene, C 19 O 4 H 16 , is reported from the viewpoint of characteristics in the helical alignments and difference compared to the crystal structure of a structural isomeric compound. The asymmetric unit of title compound contains two conformers A and B. Furthermore, the molecules in crystal exhibit atropisomerism brought about by molecular stereogenic axis of carbon-carbon bond between the carbonyl moiety and the naphthalene ring. Therefore, a pair of R - and S -enantiomeric molecules exists for each conformer. The two pairs of the enantiomeric molecules are related by two-fold helical axis in the asymmetric unit of P2 1 /c space group, exhibiting the number of molecules is eight, Z = 8. Single molecular structure of title compound shows non-coplanarly accumulated aromatic-rings structure. The molecular packing structure is mainly stabilized non-classical hydrogen bonds involving C-H…O hydrogen bonds and C-H…π ones, however O-H…O=C classical hydrogen bonds are solely formed between same configured conformers. Comparison with the spatial alignment of an isomeric homologue, 2-hydroxy-1-(4-methoxy benzoyl)-7-methoxynaphthalene, has clarified that substitution position of hydroxy group determines not only direction of classical hydrogen bonds but also total feature of molecular packing, i.e. , the homologous compound, which has hydroxy group at 2-position of naphthalene core forms intramolecular O-H…O=C classical hydrogen bond, and O-H…OMe classical hydrogen bonds between opposite enantiomeric isomers. The presence/absence and direction of the predominantly strong classical hydrogen bonds govern balance of interactions of other less effective classical and non-classical hydrogen bonds in molecular packing. In homologous compound, each of non-classical hydrogen bonds between same signed enantiomeric isomers and those between opposite enantiomeric isomers demonstrates almost same distances. In title compound, both types of non-classical hydrogen bonds formed by conformer A are imbalanced. The imbalanced non-classical hydrogen bonds are adjusted and reinforced by non-classical hydrogen bonds between conformers A and B.