C6H5O

C6H5O is commonly used to denote the phenoxy radical, a neutral aryl-oxy radical derived from phenol (C6H5OH) by removal of a hydrogen atom. The formula represents a reactive species with six carbons, five hydrogens, and one oxygen, existing as a radical rather than a stable closed-shell molecule.

Structure and properties: The unpaired electron resides on the oxygen and is delocalized into the adjacent benzene ring, giving several resonance forms. The geometry is broadly planar around the aromatic framework, and the spin density is distributed over the oxygen and neighboring ring carbons. As a radical, C6H5O is highly reactive and participates readily in radical–radical and radical–molecule reactions.

Generation and occurrence: In practice, the phenoxy radical is not isolated as a stable solid or liquid at ambient conditions. It is typically generated in situ by hydrogen abstraction from phenol, photolytic or thermal cleavage of phenolic precursors, or during combustion and atmospheric oxidation of phenolic compounds. It can be detected and studied by spectroscopic methods such as electron paramagnetic resonance (EPR).

Reactivity and role: The phenoxy radical is an important intermediate in the oxidation of phenols, atmospheric chemistry, and combustion processes. It can react with molecular oxygen to form peroxy-type intermediates, dimerize under suitable conditions, or participate in polymerization and degradation pathways.

See also: phenol, phenoxy radical, radical chemistry.