Acyl group

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Acyl radical ( blue ) as part of a molecule (top left), acylium ion, acyl radical ( top right) and as a structural element in an aldehyde (bottom left), ester and carboxamide (bottom right). (R 1 , R 2 , R 3 = organyl radical or hydrogen atom).

In chemistry, an acyl group , acyl , acyl or alkanoyl is a functional group with the general structure R- (C = O) -, where R is an organyl radical ( alkyl , aryl or heteroaromatic group, etc.) or a Is hydrogen atom. The acyl group is formally derived from carboxylic acids , aldehydes or carboxylic acid chlorides in which an OH group , a hydrogen atom or a chloride has been substituted by a radical . The introduction of an acyl group into a molecule is called acylation . The functional group without reference to a radical R , i.e. - (C = O) -, is called the carbonyl group .

The acyl group with the undefined radical R is the generic term for the acetyl group ("Ac"), the formyl group , the benzoyl group and similar radicals. The acyl group should not match the acyloxy group - e.g. B. Acetyloxygruppe ("OAc") or Benzoyloxygruppe - be confused.

Acylium ion

Mesomeric boundary structures of an acylium ion.

An acylium ion is created when the unpaired electron is released, leaving a single positively charged cation (usually R – C + = O) behind. It is easily attackable by nucleophiles and therefore plays an important role as an intermediate in organic reactions , e.g. B. Friedel-Crafts acylation .

Among other things, it is also used for the esterification of organic acids substituted in the α-position in order to circumvent the steric hindrance .

It can be produced, for example, by dissolving carboxylic acids in concentrated sulfuric acid and then reacting this solution with alcohols .

Acyl radical

The general structural formula of the acyl radical, which only occurs as a (mostly) unstable intermediate state in a reaction mechanism, is given in the figure.


formal trunk connection Remainder (R 1 ) Remainder (R 2 ) Acyl group
Formic acid -H -OH Formyl group
acetic acid -CH 3 -OH Acetyl group
Propionic acid -CH 2 CH 3 -OH Propionyl group
Butyric acid -CH 2 CH 2 CH 3 -OH Butyryl group
Valeric acid -CH 2 CH 2 CH 2 CH 3 -OH Valeryl group
Benzoic acid -C 6 H 5 -OH Benzoyl group
amino acid -OH Acylamino group
Formyl chloride -H - Cl Formyl group
Acetyl chloride -CH 3 -Cl Acetyl group
Propionyl chloride -CH 2 CH 3 -Cl Propionyl group
Butyryl chloride -CH 2 CH 2 CH 3 -Cl Butyryl group
Valeryl chloride -CH 2 CH 2 CH 2 CH 3 -Cl Valeryl group
Benzoyl chloride -C 6 H 5 -Cl Benzoyl group

See also

Wiktionary: Acyl  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. ^ Brockhaus ABC chemistry. VEB FA Brockhaus Verlag, Leipzig 1965, p. 152.
  2. Otto-Albrecht Neumüller (Ed.): Römpps Chemie-Lexikon. Volume 1: A-Cl. 8th revised and expanded edition. Franckh'sche Verlagshandlung, Stuttgart 1979, ISBN 3-440-04511-0 , p. 61.
  3. Joachim Buddrus, Bernd Schmidt: Fundamentals of Organic Chemistry , 5th edition, de Gruyter Verlag, Berlin, 2015, p. 391, ISBN 978-3-11-030559-3 .