Thiophene is a heterocyclic compound with the formula C₄H₄S. Consisting of a planar five-membered ring, it is aromatic as indicated by its extensive substitution reactions. It is a colorless liquid with a benzene-like odor. In most of its reactions, it resembles benzene. Compounds analogous to thiophene include furan (C₄H₄O), selenophene (C₄H₄Se) and pyrrole (C₄H₄NH), which each vary by the heteroatom in the ring.