ArO

ArO is a shorthand notation used in chemistry to denote an aryl-oxy fragment or a related aryl-oxy radical. In general, Ar stands for an aryl group (often a phenyl ring), and O denotes oxygen. The term can refer to both a neutral aryloxy substituent Ar-O- and to radical species such as the aryloxy radical ArO•, depending on context. The meaning is defined by the surrounding chemical notation and reaction conditions.

In organic chemistry, Ar-O- describes the aryloxy linkage found in many compounds, including phenols (ArOH) and aryloxy ethers (Ar-O-R). The aryloxy group is a common building block in synthesis, serving as a leaving group, a protecting group, or part of esters and ethers. The aryloxide anion ArO− can form by deprotonation of phenols and participates in nucleophilic substitutions and metal-catalyzed coupling reactions.

In radical chemistry, ArO• refers to aryloxy radicals arising from one-electron oxidation of phenols or hydrogen abstraction from phenolic precursors. These radicals are resonance-stabilized, with the unpaired electron delocalized over the oxygen and aromatic ring. They readily react with O2 to form peroxy-aryloxyl species (ArOO•) and can engage in various propagation or termination steps that influence oxidation processes in atmospheric chemistry, combustion, and polymerization.

Detection and study of ArO species employ techniques such as electron paramagnetic resonance (EPR) spectroscopy and UV-visible spectroscopy, alongside kinetic measurements and computational modeling to understand their formation, stability, and reactivity. See also aryloxy, phenoxy radical, and aryl ether.

---