Phenyl

In organic chemistry, the phenyl group or phenyl ring is a cyclic group of atoms with the formula C₆H₅. Phenyl groups are closely related to benzene and can be viewed as a benzene ring, minus a hydrogen, serving as a functional group. Phenyl groups have six carbon atoms bonded together in a hexagonal planar ring, five of which are bonded to individual hydrogen atoms, with the remaining carbon bonded to a substituent. Phenyl groups are commonplace in organic chemistry. Although often depicted with alternating double and single bonds, phenyl groups are chemically aromatic and show nearly equal bond lengths between carbon atoms in the ring.

Usually, a "phenyl group" is synonymous to C₆H₅– and is represented by the symbol Ph or, archaically, Φ. Benzene is sometimes denoted as PhH. Phenyl groups are generally attached to other atoms or groups. For example, triphenylmethane (Ph₃CH) has three phenyl groups attached to the same carbon center. Many or even most phenyl compounds are not described with the term "phenyl". For example, the chloro derivative C₆H₅Cl is normally called chlorobenzene, although it could be called phenyl chloride. In special (and rare) cases, isolated phenyl groups are detected: the phenyl anion (C₆H₅⁻), the phenyl cation (C₆H₅⁺), and the phenyl radical (C₆H₅^·).π

Although Ph and phenyl uniquely denote C₆H₅, substituted derivatives also are described using the phenyl terminology. For example, O₂NC₆H₄ is nitrophenyl and F₅C₆ is pentafluorophenyl. Monosubstituted phenyl groups (that is, disubstituted benzenes) are associated with electrophilic aromatic substitution reactions and the products follow the arene substitution pattern. So, a given substituted phenyl compound has three isomers, ortho (1,2-disubstitution), meta (1,3-disubstitution) and para (1,4-disubstitution). A disubstituted phenyl compound (trisubstituted benzene) may be, for example, 1,3,5-trisubstituted, or 1,2,3-trisubstituted. Higher degrees of substitution, of which the pentafluorophenyl group is an example, exist, and are named according to IUPAC nomenclature.

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