trans-2-Undecenoic acid ((E)-2-Undecenoic acid) is an α,β-unsaturated carboxylic acid and is characterized by acid dimers. The corresponding dimers are connected via intermolecular hydrogen bonds of the carboxylic groups C=O···H-O^[1]. In Vitro: The crystal packing of trans-2-Undecenoic acid (E)-undec-2-enoic acid) is described by layers of acid dimers parallel to the (0 4 1) plane which are featured by layers of polar headgroups and hydrophobic hydrocarbon chains. The carboxylic group and the following three carbon atoms (C2, C3, C4) of the trans-2-Undecenoic acid (E)-undec-2-enoic acid) molecule lie in one plane, whereas the atoms of the hydrocarbon chain starting from C4 until C11 adopt a nearly fully staggered conformation^[1].