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

The title compound, C(17)H(16)N(2)O(3), 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 carb-oxy group and the attached benzene ring is 3.2 (2)°. In the crystal, mol-ecules are oriented with the carb-oxy 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.