Thiophene is a heterocyclic compound with the formula C₄H₄S. Consisting of a flat five-membered ring, it is aromatic

Aromaticity

In organic chemistry, Aromaticity is a chemical property in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibit a stabilization stronger than would be expected by the stabilization of conjugation alone. The earliest use of the term was in an article by August...

 as indicated by its extensive substitution reactions. Related to thiophene are benzothiophene

Benzothiophene

Benzothiophene is an aromatic organic compound with a molecular formula C8H6S and an odor similar to naphthalene . It occurs naturally as a constituent of petroleum-related deposits such as lignite tar. Benzothiophene has no household use...

 and dibenzothiophene

Dibenzothiophene

Dibenzothiophene is the organosulfur compound consisting of two benzene rings fused to a central thiophene ring. It is a colourless solid that is chemically somewhat similar to anthracene...

, containing the thiophene ring fused with one and two benzene rings, respectively. Compounds analogous to thiophene include furan

Furan

Furan is a heterocyclic organic compound, consisting of a five-membered aromatic ring with four carbon atoms and one oxygen. The class of compounds containing such rings are also referred to as furans....

 (C₄H₄O) and pyrrole

Pyrrole

Pyrrole is a heterocyclic aromatic organic compound, a five-membered ring with the formula C4H4NH. It is a colourless volatile liquid that darkens readily upon exposure to air. Substituted derivatives are also called pyrroles, e.g., N-methylpyrrole, C4H4NCH3...

 (C₄H₄NH).
Thiophene was discovered as a contaminant in benzene.