The rhodanine derivatives are a group of com­pounds known for their pharmacological action. Four new crystal structures of 3-[5-(chloro­benzyl­idene)rhodanine]propionic acid isomers, characterized by X-ray diffraction analysis and theoretical calculations, are reported. 3-[5-(2-Chloro­benzyl­idene)-4-oxo-2-sulfanyl­idene-1,3-thia­zoliden-3-yl]propanoic acid, , 1, crystallizes in the space group , with one mol­ecule in the asymmetric unit. The other com­pounds, namely, 3-[5-(3-chloro­benzyl­idene)-4-oxo-2-sulfanyl­idene-1,3-thia­zoliden-3-yl]propanoic acid, , 2 and its polymorph 2p, and 3-[5-(4-chloro­benzyl­idene)-4-oxo-2-sulfanyl­idene-1,3-thia­zoliden-3-yl]pro­pan­oic acid, C13H10ClNO3S2, 3, crystallize in the triclinic centrosymmetric space group, with one mol­ecule in the asymmetric unit. The geometry of the created polymorphs indicates differences in the conformation of the carb­oxy­ethyl moiety and the position of the chlorine substituent on the aromatic ring. The crystal packing in all four presented crystal structures is dominated by inter­molecular O—H⋯O hy­dro­gen bonds. The calculated energies of the presented com­pounds show that the most biologically active, i.e. 1, has the lowest stability, while the least active, i.e. 3, is the most stable. Several theoretical descriptors were used to correlate the structural features of the studied com­pounds with their biological activity.