Thiophene

Thiophene is a five-membered aromatic ring containing four carbon atoms and one sulfur atom. Its aromatic π system includes one sulfur lone pair.

Aromaticity: A stabilizing electronic condition in which a cyclic, conjugated molecule has delocalized π electrons. Thiophene’s delocalized six-electron π system makes it aromatic.
Electrophilic aromatic substitution: A reaction in which an electrophile replaces a hydrogen on an aromatic ring. Thiophene commonly undergoes substitution rather than addition, retaining aromaticity.
Polythiophene: A family of conjugated polymers made from linked thiophene units. Oxidized polythiophenes conduct electricity and are used in electronic materials.
Victor Meyer: A German chemist known for work on organic chemistry and the development of vapor-density methods. Meyer discovered thiophene in benzene fractions from coal tar in 1882.
Heterocyclic compound: A cyclic compound whose ring contains at least one atom other than carbon. Sulfur replaces one carbon in thiophene’s five-membered ring.
2-Substitution: Replacement of a substituent or hydrogen at position 2 of a five-membered heteroaromatic ring. Electrophilic attack on thiophene usually favors its 2-position.
Poly(3-hexylthiophene): A semiconducting polymer built from 3-hexylthiophene units. It is a widely studied thiophene-based material for organic electronics.
Coal tar: A complex liquid mixture produced during the destructive distillation of coal. Thiophene was first isolated from coal-tar-derived benzene.
Hückel's rule: A rule predicting aromaticity in planar, cyclic, conjugated systems with 4n+2 π electrons. Thiophene has six π electrons, satisfying the rule for aromaticity.
3-Substitution: Replacement of a substituent or hydrogen at position 3 of a five-membered heteroaromatic ring. Substitution here is less favored than at thiophene’s 2-position.

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