Phenylenyl

Phenylenyl is a chemical term used to describe an aryl fragment derived from benzene by removal of two hydrogen atoms, resulting in a C6H4 core with two available valences. It is distinguished from the phenyl group (C6H5–), which has a single valence. The phenylenyl fragment may act as a divalent linker in a range of compounds, or as the core of a radical species in certain contexts.

There are three principal isomers of phenylenyl corresponding to which two hydrogens on the benzene ring are removed: 1,2-phenylenyl (ortho), 1,3-phenylenyl (meta), and 1,4-phenylenyl (para). In many discussions, the related term phenylenediyl is used when the fragment serves as a bridging unit between two partners, such as in polymers or coordination assemblies.

In practical chemistry, phenylenyl and phenylenediyl fragments appear in polymer science, organometallic chemistry, and the study of biradicaloid systems. For example, para-oriented phenylenyl linkers are encountered in poly(p-phenylene) materials and in various diaryl linkage motifs. The phenylenyl radical, a related species with an unpaired electron on the ring, is also described in radical chemistry and can participate in coupling or electron-transfer processes.

Nomenclature can vary, and the term phenylenyl is less common in everyday organic synthesis than phenyl or phenylene. It is typically encountered in discussions of aryl diradicals, bridging units in polymers, or when specifying ring positions for divalent aryl fragments.

See also: phenyl, phenylene, phenylenediamine, polyphenylene.