Mesomorphism dependence on ortho-substituted lateral groups in isomeric and nonisomeric homologous series

A novel monomeric homologous series of α,β-ethylene derivatives was synthesized and studied with a view to understanding and establishing the relation between molecular structure and liquid crystal properties. The series consists of 12 novel compounds. The methoxy to propyloxy derivatives are not liquid crystals, the butyloxy homologue is monotropic nematic, the pentyloxy homologue is monotropic smectic and enantiotropic nematic, and the rest of the homologues (C6–C16) are enantiotropically smectic in addition to nematic. Transition temperatures and texture were determined by an optical polarizing microscope equipped with a heating stage, and show an odd–even effect for nematic–isotropic and smectic–nematic transition curves. Analytical and spectral data confirm the molecular structures. The average smectic and nematic thermal stabilities are 84.9°C and 94.15°C, respectively. The liquid crystal properties of present series are compared with the structurally similar known series.