# Acetyl group

In organic chemistry, an acetyl group is a functional group denoted by the chemical formula −COCH$_3$ and the structure −C(=O)−CH$_3$. It is sometimes represented by the symbol Ac (not to be confused with the element actinium). In IUPAC nomenclature, an acetyl group is called an ethanoyl group.
An acetyl group contains a methyl group (−CH$_3$) that is single-bonded to a carbonyl (C=O), making it an acyl group. The carbonyl center of an acyl radical has one non-bonded electron with which it forms a chemical bond to the remainder (denoted with the letter R) of the molecule.
The acetyl moiety is a component of many organic compounds, including acetic acid, the neurotransmitter acetylcholine, acetyl-CoA, acetylcysteine, acetaminophen (also known as paracetamol), and acetylsalicylic acid (also known as aspirin).

## Acetylation

The process of adding an acetyl group into a molecule is called acetylation. An example of an acetylation reaction is the conversion of glycine to N-acetylglycine:
    H$_2$NCH$_2$CO$_2$H + (CH$_3$CO)$_2$O → CH$_3$C(O)NHCH$_2$CO$_2$H + CH$_3$CO$_2$H

### In biology

Enzymes which perform acetylation on proteins or other biomolecules are known as acetyltransferases. In biological organisms, acetyl groups are commonly transferred from acetyl-CoA to other organic molecules. Acetyl-CoA is an intermediate in the biological synthesis and in the breakdown of many organic molecules. Acetyl-CoA is also created during the second stage of cellular respiration (pyruvate decarboxylation) by the action of pyruvate dehydrogenase on pyruvic acid.
Proteins are often modified via acetylation, for various purposes. For example, acetylation of histones by histone acetyltransferases (HATs) results in an expansion of local chromatin structure, allowing transcription to occur by enabling RNA polymerase to access DNA. However, removal of the acetyl group by histone deacetylases (HDACs) condenses the local chromatin structure, thereby preventing transcription.

### In synthetic organic and pharmaceutical chemistry

Acetylation can be achieved by chemists using a variety of methods, most commonly with the use of acetic anhydride or acetyl chloride, often in the presence of a tertiary or aromatic amine base.

## Pharmacology

Acetylated organic molecules exhibit increased ability to cross the selectively permeable blood–brain barrier. Acetylation helps a given drug reach the brain more quickly, making the drug's effects more intense and increasing the effectiveness of a given dose. The acetyl group in acetylsalicylic acid (aspirin) enhances its effectiveness relative to the natural anti-inflammatant salicylic acid. In similar manner, acetylation converts the natural painkiller morphine into the far more potent heroin (diacetylmorphine).
There is some evidence that acetyl-L-carnitine may be more effective for some applications than L-carnitine. Acetylation of resveratrol holds promise as one of the first anti-radiation medicines for human populations.

## Etymology

The term "acetyl" was coined by the German chemist Justus von Liebig in 1839 to describe what he incorrectly believed to be the radical of acetic acid (the main component of vinegar, aside from water), which is now known as the vinyl group (coined in 1851); "acetyl" is derived from the Latin acētum, meaning "vinegar." When it was shown that Liebig's theory was wrong and acetic acid had a different radical, his name was carried over to the correct one, but the name of acetylene (coined in 1860) was retained.