4-{(E)-2-[4-(But-3-en-1-yl­oxy)phen­yl]diazen-1-yl}benzoic acid

The title compound, C17H16N2O3, has an E conformation about the azobenzene (–N=N–) linkage. The benzene rings are twisted slightly with respect to each other [6.79 (9)°], while the dihedral angle between the plane through the carb­oxy group and the attached benzene ring is 3.2 (2)°. In the crystal, mol­ecules are oriented with the carb­oxy groups head-to-head, forming O—H⋯O hydrogen-bonded inversion dimers. These dimers are connected by C—H⋯O hydrogen-bonds into layers lying parallel to the (013) plane.