CH3COOO

CH3COOO is the condensed formula often used for the peroxyacetyl radical CH3COOO•, an important reactive intermediate in combustion and atmospheric chemistry. In written form without the radical dot, CH3COOO can be seen as the neutral fragment, but in most chemical contexts the species is a radical and highly reactive.

The radical has a peroxyacyl structure, with an acetyl group (CH3CO–) bound to a peroxide moiety (–OO•). The unpaired electron is localized on the terminal oxygen, giving it typical RO2-like reactivity. Peroxyacetyl radicals are short-lived and participate in rapid chain-branching and propagation steps that drive oxidation processes.

Formation of CH3COOO• occurs in situ from smaller radicals. A common route is the reaction of an acetyl radical CH3CO• with molecular oxygen: CH3CO• + O2 → CH3COOO•. It can also arise from the oxidation of acetaldehyde or other acetyl-containing species in the presence of oxygen and atmospheric radicals.

In atmospheric chemistry, CH3COOO• plays a central role in the formation of secondary pollutants. It readily reacts with NO to yield the acetoxy radical CH3COO• and NO2: CH3COOO• + NO → CH3COO• + NO2. It can also react with NO2 to form peroxynitrate species such as PAN (peroxyacetyl nitrate), CH3COONO2, a key component of photochemical smog and indoor/outdoor air chemistry.

Because CH3COOO• is a transient radical, it is typically studied and referenced in mechanistic schemes and kinetic models rather than isolated as a stable compound. Safety considerations focus on the reactive, oxidizing nature of peroxy radicals and their participation in exothermic chain reactions.