Two recently synthesised diepoxy compounds based on the same rigid central segment with carbon chains of different lengths were compared. Microscopic observations, differential scanning calorimetry (DSC) and dielectric measurements confirmed the existence of a mesophase in both compounds and enabled determination of the temperatures of phase transitions. Wide-angle X-ray scattering (WAXS) measurements and optical observations enabled identification of mesophase types. Nematic phase appeared in both compounds; in the material with longer chains smectic A phase was also detected. Lengths of the molecules and average nearest neighbor distances were estimated using the wide-angle X-ray scattering results. Lengths of the molecules were also computed by quantum mechanical methods resulting in very good agreement with the experimental data.