4-Hexadecyloxyphenyl-4-substituted benzoates, Ia-d, and 4-substituted phenyl-4- hexadecyloxy benzoates, IIa-d, with the substituents CH3O, Cl, CN, and NO2, respectively, were prepared and characterized by infrared spectroscopy and the apparent solution dipole moment measured using cyclohexane as a solvent. Smectic A mesophase stability was investigated by differential scanning calorimetry and polarized light microscopy. The effects of structural changes on phase transitions in these two series of compounds are discussed in terms of dipole and mesomeric effects.