Ethyl 4 '-n-undecyloxybiphenyl-4-carboxylate, 2(11)OBC, and 4 '-n-undecyloxybiphenyl-4-carboxylic acid, (11)OBC, are smectic liquid crystals precursors of low molecular weight premesogens, and of potential liquid crystal macromolecules. The single-crystal X-ray study of 2(11)OBC showed that it crystallizes in a non-centrosymmetric space group with molecules stacked along the short axis [010] and [001] without significant pi center dot center dot center dot pi or CH center dot center dot center dot pi interactions. Such an arrangement may explain its strong tendency to form smectic mesophases. Both biphenyl derivatives have a rich polymesomorphism whose phase sequences were determined by DSC, optical microscopy and diffraction profiles using synchrotron radiation. These profiles indicated quite similar phase transitions in the two samples, although very different transition temperatures. Thus, the phase transitions (on cooling) of 2(11)OBC are: Isotropic -> SmA (101 degrees C)-> SmB (88 degrees C)-> SE (79 degrees C)-> crystal phase (43 degrees C), while those (on cooling) of (11)OBC are the following: Isotropic -> SmA (246 degrees C)-> SmB (192 degrees C)-> SX (162 degrees C)-> SE (148 degrees C)-> crystal phase (62 degrees C). The much higher transition temperatures for the acid derivative are explained by considering that this molecule forms dimers through classical O-H center dot center dot center dot O hydrogen bonds involving the carboxylic groups.