OAc

OAc is a common shorthand in chemistry for the acetate group and related acetyl-derived substituents. Depending on context, it can denote the acetate anion, OAc− (CH3COO−), as found in salts such as sodium acetate, or the acetoxy substituent, −O−COCH3, when an oxygen atom bears an acetyl group in esters and acetylated compounds.

In synthetic chemistry, OAc marks an acetyl group transferred to an oxygen atom to form acetyl esters (R-OAc). Acetylation is typically accomplished with acetyl donors such as acetic anhydride (Ac2O) or acetyl chloride (AcCl). The acetyl group can protect alcohols as acetate esters or otherwise modify alcohol reactivity, and it can be removed by hydrolysis under acidic or basic conditions.

OAc is also used in carbohydrate and polymer chemistry to denote acetylated oxygen substituents, such as acetylated sugars where multiple hydroxyl groups are masked as acetates (often written as OAc in structural descriptions). In salts, OAc refers to the acetate counterion, as in NaOAc or KOAc.

Chemically related species include methyl acetate and other acetates, which are esters formed from acetic acid and an alcohol. Hydrolysis or saponification of acetates yields alcohols and acetic acid; under basic conditions, the reaction forms acetate salts. The term OAc thus has dual usage: it can describe the acetate anion in salts or the acetoxy substituent in esters and acetylated compounds, with context determining interpretation.