Phase transitions and crystal structures of substituted alkoxyaryls

The thermal properties of a series of substituted alkoxyaryls 1–5 and N-(n-butyloxybenzylidene)-p-propiophenone (6) were studied by differential scanning calorimetry. The phase transition temperatures and heats were determined. Compounds 1–5 do not form a mesophase during the melting process, unlike compound 6, which sbows several liquid-crystalline transitions. To explain the thermal properties, crystals of compound 4, containing sulfonyl fluoride and amino groups, and compound 6 were studied by X-ray diffraction at different temperatures. The crystal packing of 4 consists of dimers connected by weak hydrogen bonds and is composed of alternating aliphatic and aromatic regions. The absence of mesomorphism in compounds 1–5 can be attributed to the dominant role of a long (C₁₄—C₁₈) alkyl substituent in the formation of the packing. In the crystal packing of 6, there are clearly distinguished loose aliphatic and dense aromatic regions. Along with the stabilizing C—H⋯π and C—O⋯H interactions, this packing allows the existence of several liquid-crystalline phases on heating.