Hydrogen bonding between aromatic H and F groups leading to a stripe structure with R- and S-columns: the crystal structure of (2,7-dimethoxynaphthalen-1-yl)(3-fluorophenyl)methanone and comparison with its 1-aroylnaphthalene analogues

In the molecule of (2,7-dimethoxynaphthalen-1-yl)(3-fluorophenyl)methanone, C19H15FO3, (I), the dihedral angle between the plane of the naphthalene ring system and that of the benzene ring is 85.90 (5)°. The molecules exhibit axial chirality, with either an R- or an S-stereogenic axis. In the crystal structure, each enantiomer is stacked into a columnar structure and the columns are arranged alternately to form a stripe structure. A pair of (methoxy)C-H...F hydrogen bonds and π-π interactions between the benzene rings of the aroyl groups link an R- and an S-isomer to form a dimeric pair. These dimeric pairs are piled up in a columnar fashion through (benzene)C-H...O=C and (benzene)C-H...OCH3 hydrogen bonds. The analogous 1-benzoylated compound, namely (2,7-dimethoxynaphthalen-1-yl)(phenyl)methanone [Kato et al. (2010). Acta Cryst. E66, o2659], (II), affords three independent molecules having slightly different dihedral angles between the benzene and naphthalene rings. The three independent molecules form separate columns and the three types of column are connected to each other via two C-H...OCH3 hydrogen bonds and one C-H...O=C hydrogen bond. Two of the three columns are formed by the same enantiomeric isomer, whereas the remaining column consists of the counterpart isomer. In the case of the fluorinated 1-benzoylated naphthalene analogue, namely (2,7-dimethoxynaphthalen-1-yl)(4-fluorophenyl)methanone [Watanabe et al. (2011). Acta Cryst. E67, o1466], (III), the molecular packing is similar to that of (I), i.e. it consists of stripes of R- and S-enantiomeric columns. A pair of C-H...F hydrogen bonds between R- and S-isomers, and C-H...O=C hydrogen bonds between R(or S)-isomers, are also observed. Consequently, the stripe structure is apparently induced by the formation of R...S dimeric pairs stacked in a columnar fashion. The pair of C-H...F hydrogen bonds effectively stabilizes the dimeric pair of R- and S-enantiomers. In addition, the co-existence of C-H...F and C-H...O=C hydrogen bonds makes possible the formation of a structure with just one independent molecule.