Crystal structure of p-n-decyloxybenzoic acid

Abstract

The crystal structure of the mesogenic title compound has been determined by single-crystal X-ray diffraction studies from 5 994 reflections. Crystals are triclinic with cell dimensions a= 8.115(1), b= 21.618(2), c= 4.820(1)Å, α= 94.07(1), β= 102.91(2), γ= 80.95(1)°, space group P, and Z= 2. The structure was determined by a direct method and refined by a least-squares procedure to R 0.0584.

The molecules are paired by hydrogen bonding between the carboxy-groups, the two halves of the dimer being related by a centre of symmetry. The two benzene rings and the two carboxy-groups of each dimer form a near-planar assembly and the alkyl chains are in the fully extended conformation.

In the crystal the aliphatic chains and the aromatic rings are segregated into alternating sheets. In the aliphatic regions the chains are interleaved and lie at an angle of ca. 12° to the sheet normal.

A statistical randomisation of the two possible hydrogen-bonding schemes between the carboxy-groups was found. The bond lengths in the groups were found to be perfectly normal and we suggest that anomalous values reported for the butoxy-compound by previous workers may result from an incomplete structure refinement.

This crystal structure is compared with those of lower homologues and the implications concerning the structure of the higher-temperature crystalline form and of the smetic C phase are discussed.