This paper describes the thermotropic polymorphic behavior of a set of new compounds carrying a variety of Y endgroups : [GRAPHICS] with Y = HOOC-, CH3OCO-, CH3CH2CO-, and CH3NHCO-. Of these compounds only the ester derivative proved capable of producing liquid crystals in the pure state. The absence of mesomorphic behavior in the other derivatives is due to the high thermal stability of the crystalline phases, as shown by a systematic study of their binary mixtures with the previously reported Y=NC-compound.