C6H5

C6H5 denotes the phenyl group, a hydrocarbon substituent that consists of a benzene ring minus one hydrogen. In common chemical notation the phenyl group is written as C6H5- or Ph- when attached to another atom or molecule. The same formula can refer to the phenyl radical, C6H5•, a reactive species formed by removing one hydrogen from benzene.

Structure and properties: The phenyl group is based on a six-carbon ring with aromatic character. The carbons are sp2-hybridized, the ring is planar, and electrons are delocalized across the ring, giving stability. Typical bond lengths are around 1.39 Å for carbon–carbon bonds and about 1.08 Å for carbon–hydrogen bonds. The ring imparts characteristic chemical behavior, including susceptibility to electrophilic substitution at various positions on the ring.

Reactivity and role: As a substituent, the phenyl group influences the physical and chemical properties of larger molecules, contributing hydrophobicity and a site for reactions on the ring. The phenyl radical form is highly reactive and short-lived under normal conditions. In organic synthesis, the phenyl group is often denoted Ph- in reaction schemes and is a common building block in a wide range of compounds.

Examples and applications: The phenyl group appears in many substances, such as phenyl chloride (C6H5Cl), acetophenone (C6H5COCH3), and aniline (C6H5NH2). It is prevalent in pharmaceuticals, dyes, plastics, and polymers, where it influences color, stability, and interactions.

Distinctions: C6H5 is distinct from benzene (C6H6) and from the benzyl group (C6H5CH2–), which includes a methylene linker to additional atoms.