Acetic anhydride, or ethanoic anhydride, is the chemical compound

Chemical compound

A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

 with the formula

Chemical formula

A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....

 (CH₃CO)₂O. Commonly abbreviated Ac

Acetyl

In organic chemistry, acetyl is a functional group, the acyl with chemical formula COCH3. It is sometimes represented by the symbol Ac . The acetyl group contains a methyl group single-bonded to a carbonyl...

₂O, it is the simplest isolatable acid anhydride and is a widely used reagent

Reagent

A reagent is a "substance or compound that is added to a system in order to bring about a chemical reaction, or added to see if a reaction occurs." Although the terms reactant and reagent are often used interchangeably, a reactant is less specifically a "substance that is consumed in the course of...

 in organic synthesis

Organic synthesis

Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...

. It is a colorless liquid that smells strongly of acetic acid

Acetic acid

Acetic acid is an organic compound with the chemical formula CH3CO2H . It is a colourless liquid that when undiluted is also called glacial acetic acid. Acetic acid is the main component of vinegar , and has a distinctive sour taste and pungent smell...

, formed by its reaction with the moisture in the air.

Formic anhydride

Formic anhydride

Formic anhydride, also called methanoic anhydride, is a chemical compound with formula or 2O. It can be viewed as the anhydride of formic acid ....

 is an even simpler acid anhydride, but it spontaneously decomposes, especially once removed from solution.
Contrary to what its Lewis structure

Lewis structure

Lewis structures are diagrams that show the bonding between atoms of a molecule and the lone pairs of electrons that may exist in the molecule. A Lewis structure can be drawn for any covalently bonded molecule, as well as coordination compounds...

 seems to predict, acetic anhydride, like many other acid anhydrides that are free to rotate, has experimentally been found to be aplanar.