Arene substitution pattern

An arene substitution pattern describes the positions of substituents on an aromatic ring relative to one another. In benzene derivatives, the common patterns are ortho, meta, and para.

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Arene: An aromatic hydrocarbon containing one or more rings with delocalized π electrons. Arene substitution patterns describe how groups occupy positions on these aromatic rings.
Electrophilic aromatic substitution: A reaction in which an electrophile replaces a hydrogen atom on an aromatic ring while aromaticity is restored. Existing substituents direct incoming groups toward characteristic positions on the ring.
Ortho, meta, and para: Terms describing 1,2-, 1,3-, and 1,4-substitution relationships on a benzene ring. These names are the most familiar shorthand for benzene substitution patterns.
Numbering of fused aromatic rings: The system for assigning positions in aromatic compounds made from fused rings, such as naphthalene. Fused-ring numbering cannot be reduced to benzene’s ortho, meta, and para shorthand.
Benzene: A six-carbon aromatic hydrocarbon with a planar ring and delocalized π electrons. Its six equivalent ring positions make the standard ortho, meta, and para patterns easy to define.
Ortho–para director: A substituent that generally favors electrophilic substitution at the ortho and para positions of an aromatic ring. These groups shape the substitution patterns formed in sequential aromatic reactions.
Disubstituted benzene: A benzene derivative in which two ring hydrogens have been replaced by substituents. Its three positional isomers show how a pattern can change molecular identity.
Aryl group: A group derived from an aromatic ring by removing one hydrogen atom. Aryl names describe a substituent attached elsewhere, not the arrangement of groups on its ring.
Aromaticity: The unusual stability of certain cyclic, conjugated molecules with delocalized electrons. Aromaticity defines the ring framework whose positions substitution patterns describe.
Meta director: A substituent that generally favors electrophilic substitution at the meta position of an aromatic ring. Meta-directing groups produce a distinct positional outcome in further ring substitution.