Molecular and crystal structures of mesomorphic aromatic esters: I. Structure of two isomers, p-butoxyphenyl p′-hexyloxybenzoate and p-hexyloxyphenyl p′-butoxybenzoate

Two isomers, p-butoxyphenyl p′-hexyloxybenzoate (1) and p-hexyloxyphenyl p′-butoxybenzoate (2), are studied by X-ray diffraction. Crystals 1 contain two crystallographically independent molecules, which differ in the conformation of one of their side chains. In both compounds, bond lengths and angles have standard values. The geometry of the central fragment Ph-Est-Ph is essentially the same in both isomers. One of the benzene rings is coplanar with the Est group, and the other ring, which is linked with this group through the oxygen atom, is almost perpendicular to the Est plane. In crystal 1, molecules are packed in such a fashion that, in any pair of neighboring molecules, the most closely spaced benzene rings are nearly perpendicular to each other, which corresponds to a weak C-H⋯π interaction. In the crystal packing of 2, neither perpendicular nor stacking motifs are observed. The supramolecular architecture of this compound is determined by directional specific interactions of the hydrogen bond type between the C-H benzene fragment and the ester oxygen atom of the neighboring molecule.