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In chemistry, an acyl group is a
moiety Moiety may refer to: Chemistry * Moiety (chemistry), a part or functional group of a molecule ** Moiety conservation, conservation of a subgroup in a chemical species Anthropology * Moiety (kinship), either of two groups into which a society is ...
derived by the removal of one or more
hydroxyl In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydro ...
groups from an
oxoacid An oxyacid, oxoacid, or ternary acid is an acid that contains oxygen. Specifically, it is a compound that contains hydrogen, oxygen, and at least one other element, with at least one hydrogen atom bonded to oxygen that can dissociate to produce ...
, including
inorganic acid A mineral acid (or inorganic acid) is an acid derived from one or more inorganic compounds, as opposed to organic acids which are acidic, organic compounds. All mineral acids form hydrogen ions and the conjugate base when dissolved in water. Char ...
s. It contains a double-bonded
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
atom Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons. Every solid, liquid, gas, ...
and an
alkyl group In organic chemistry, an alkyl group is an alkane missing one hydrogen. The term ''alkyl'' is intentionally unspecific to include many possible substitutions. An acyclic alkyl has the general formula of . A cycloalkyl is derived from a cycloalk ...
(). In
organic chemistry Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clayden, ...
, the acyl group (
IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...
name: alkanoyl) is usually derived from a carboxylic acid, in which case it has the formula , where R represents an
alkyl group In organic chemistry, an alkyl group is an alkane missing one hydrogen. The term ''alkyl'' is intentionally unspecific to include many possible substitutions. An acyclic alkyl has the general formula of . A cycloalkyl is derived from a cycloalk ...
that is linked to the
carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon mak ...
atom of the group by a single bond. Although the term is almost always applied to organic compounds, acyl groups can in principle be derived from other types of acids such as sulfonic acids and phosphonic acids. In the most common arrangement, acyl groups are attached to a larger molecular fragment, in which case the carbon and oxygen atoms are linked by a
double bond In chemistry, a double bond is a covalent bond between two atoms involving four bonding electrons as opposed to two in a single bond. Double bonds occur most commonly between two carbon atoms, for example in alkenes. Many double bonds exist betwee ...
.


Compounds

Well-known acyl compounds are the acyl chlorides, such as
acetyl chloride Acetyl chloride (CH3COCl) is an acyl chloride derived from acetic acid. It belongs to the class of organic compounds called acid halides. It is a colorless, corrosive, volatile liquid. Its formula is commonly abbreviated to AcCl. Synthesis On a ...
(CH3COCl) and
benzoyl chloride Benzoyl chloride, also known as benzenecarbonyl chloride, is an organochlorine compound with the formula . It is a colourless, fuming liquid with an irritating odour, and consists of a benzene ring () with an acyl chloride () substituent. It is ...
(C6H5COCl). These compounds, which are treated as sources of acylium cations, are good reagents for attaching acyl groups to various substrates.
Amide In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a compound with the general formula , where R, R', and R″ represent organic groups or hydrogen atoms. The amide group is called a peptide bond when it i ...
s (RC(O)NR2) and
ester In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides a ...
s (RC(O)OR′) are classes of acyl compounds, as are ketones (RC(O)R) and
aldehyde In organic chemistry, an aldehyde () is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl grou ...
s (RC(O)H).


Acylium cations, radicals, and anions

Acylium ions are cations of the formula . The carbon–oxygen
bond length In molecular geometry, bond length or bond distance is defined as the average distance between nuclei of two bonded atoms in a molecule. It is a transferable property of a bond between atoms of fixed types, relatively independent of the rest of ...
in these cations is near 1.1  Å (110-112 pm), which is shorter than the 112.8 pm of
carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
and indicates
triple-bond A triple bond in chemistry is a chemical bond between two atoms involving six bonding electrons instead of the usual two in a covalent single bond. Triple bonds are stronger than the equivalent single bonds or double bonds, with a bond order ...
character. The carbon centres of acylium ions generally have a linear geometry and sp atomic hybridization, and are best represented by a
resonance structure In chemistry, resonance, also called mesomerism, is a way of describing bonding in certain molecules or polyatomic ions by the combination of several contributing structures (or ''forms'', also variously known as ''resonance structures'' or '' ...
bearing a formal positive charge on the oxygen (rather than carbon): . They are characteristic fragments observed in EI-
mass spectra A mass spectrum is a histogram plot of intensity vs. ''mass-to-charge ratio'' (''m/z'') in a chemical sample, usually acquired using an instrument called a ''mass spectrometer''. Not all mass spectra of a given substance are the same; for example ...
of ketones. Acylium ions are common reactive intermediates, for example in the Friedel–Crafts acylation and many other organic reactions such as the
Hayashi rearrangement The Hayashi rearrangement is the chemical reaction of ''ortho''-benzoylbenzoic acids catalysis, catalyzed by sulfuric acid or phosphorus pentoxide. This reaction proceeds through electrophilic acylium ion attack with a Spiro compound, spiro inter ...
. Salts containing acylium ions can be generated by removal of the halide from
acyl halide In organic chemistry, an acyl halide (also known as an acid halide) is a chemical compound derived from an oxoacid by replacing a hydroxyl group () with a halide group (, where X is a halogen). If the acid is a carboxylic acid (), the compoun ...
s: :RC(O)Cl + SbCl5 -> CO bCl6 Acyl radicals are readily generated from aldehydes by hydrogen-atom abstraction. However, they undergo rapid
decarbonylation Decarbonylation is a type of organic reaction that involves loss of CO. It is often an undesirable reaction since it represents a degradation. In the chemistry of metal carbonyls, decarbonylation describes a substitution process, whereby a CO lig ...
to afford the alkyl radical: :\ce^\bullet \ce^\bullet + \ce Acyl
anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...
s are almost always unstable—usually too unstable to be exploited synthetically. They readily react with the neutral aldehyde to form an
acyloin Acyloins or α-hydroxy ketones are a class of organic compounds which all possess a hydroxy group adjacent to a ketone group. The name acyloin is derived from the fact that they are formally derived from reductive coupling of carboxylic acyl grou ...
dimer. Hence, synthetic chemists have developed various acyl anion synthetic equivalents, such as
dithiane A dithiane is a heterocyclic compound composed of a cyclohexane core structure wherein two methylene bridges (-- units) are replaced by sulfur centres. The three isomeric parent heterocycles are 1,2-dithiane, 1,3-dithiane and 1,4-dithiane. 1,3 ...
s, as surrogates. However, as a partial exception, hindered dialkylformamides (e.g., diisopropylformamide, HCON''i''Pr2) can undergo deprotonation at low temperature (−78 °C) with
lithium diisopropylamide Lithium diisopropylamide (commonly abbreviated LDA) is a chemical compound with the molecular formula . It is used as a strong base and has been widely utilized due to its good solubility in non-polar organic solvents and non-nucleophilic nature ...
as the base to form a
carbamoyl Carbamic acid, which might also be called aminoformic acid or aminocarboxylic acid, is the chemical compound with the formula . It can be obtained by the reaction of ammonia and carbon dioxide at very low temperatures, which also yields an equ ...
anion stable at these temperatures.


In biochemistry

In
biochemistry Biochemistry or biological chemistry is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology and ...
there are many instances of acyl groups, in all major categories of biochemical molecules. Acyl-CoAs are acyl derivatives formed via
fatty acid In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, ...
metabolism. Acetyl-CoA, the most common derivative, serves as an acyl donor in many biosynthetic transformations. Such acyl compounds are
thioester In organic chemistry, thioesters are organosulfur compounds with the functional group . They are analogous to carboxylate esters () with the sulfur in the thioester playing the role of the linking oxygen in the carboxylate ester, as implied by t ...
s. Names of acyl groups of
amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha a ...
s are formed by replacing the ''-ine'' suffix with ''-yl''. For example, the acyl group of
glycine Glycine (symbol Gly or G; ) is an amino acid that has a single hydrogen atom as its side chain. It is the simplest stable amino acid ( carbamic acid is unstable), with the chemical formula NH2‐ CH2‐ COOH. Glycine is one of the proteinog ...
is
glycyl Glycine (symbol Gly or G; ) is an amino acid that has a single hydrogen atom as its side chain. It is the simplest stable amino acid (carbamic acid is unstable), with the chemical formula In chemistry, a chemical formula is a way of pres ...
, and of lysine is
lysyl Lysine (symbol Lys or K) is an α-amino acid that is a biosynthesis, precursor to many proteins. It contains an α-amino group (which is in the protonation, protonated form under biological conditions), an α-carboxylic acid group (which is in ...
. Names of acyl groups of
ribonucleoside monophosphate In biochemistry, a ribonucleotide is a nucleotide containing ribose as its pentose component. It is considered a molecular precursor of nucleic acids. Nucleotides are the basic building blocks of DNA and RNA. Ribonucleotides themselves are basic ...
s such as
AMP #REDIRECT Amp {{Redirect category shell, {{R from other capitalisation{{R from ambiguous page ...
(5′-adenylic acid),
GMP GMP may refer to: Finance and economics * Gross metropolitan product * Guaranteed maximum price * Guaranteed Minimum Pension Science and technology * GNU Multiple Precision Arithmetic Library, a software library * Granulocyte-macrophage progenito ...
(5′-guanylic acid), CMP (5′-cytidylic acid), and UMP (5′-uridylic acid) are adenylyl, guanylyl, cytidylyl, and uridylyl respectively. In phospholipids, the acyl group of
phosphatidic acid Phosphatidic acids are anionic phospholipids important to cell signaling and direct activation of lipid-gated ion channels. Hydrolysis of phosphatidic acid gives rise to one molecule each of glycerol and phosphoric acid and two molecules of fatty ac ...
is called phosphatidyl-. Finally, many
saccharide In organic chemistry, a carbohydrate () is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula (where ''m'' may or ma ...
s are acylated.


In organometallic chemistry and catalysis

Acyl
ligand In coordination chemistry, a ligand is an ion or molecule ( functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's elec ...
s are intermediates in many
carbonylation Carbonylation refers to reactions that introduce carbon monoxide into organic and inorganic substrates. Carbon monoxide is abundantly available and conveniently reactive, so it is widely used as a reactant in industrial chemistry. The term carbony ...
reactions, which are important in some catalytic reactions. Metal acyls arise usually via insertion of
carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
into metal–
alkyl In organic chemistry, an alkyl group is an alkane missing one hydrogen. The term ''alkyl'' is intentionally unspecific to include many possible substitutions. An acyclic alkyl has the general formula of . A cycloalkyl is derived from a cycloa ...
bonds. Metal acyls also arise from reactions involving acyl chlorides with low-valence metal complexes or by the reaction of organolithium compounds with metal carbonyls. Metal acyls are often described by two resonance structures, one of which emphasizes the
basicity In chemistry, there are three definitions in common use of the word base, known as Arrhenius bases, Brønsted bases, and Lewis bases. All definitions agree that bases are substances that react with acids, as originally proposed by G.-F. ...
of the oxygen center. ''O''-alkylation of metal acyls gives
Fischer carbene A Fischer carbene is a divalent organic ligand in an organometallic compound. In a Fischer carbene, the carbene ligand is a σ-donor π-acceptor ligand. Because π-backdonation from the metal centre is generally weak, the carbene carbon is electr ...
complexes.


Nomenclature

The common names of acyl groups are derived typically by replacing the -ic acid suffix of the corresponding carboxylic acid's common name with -yl (or -oyl), as shown in the table below. In the
IUPAC nomenclature of organic chemistry In chemical nomenclature, the IUPAC nomenclature of organic chemistry is a method of naming organic chemical compounds as recommended by the International Union of Pure and Applied Chemistry (IUPAC). It is published in the '' Nomenclature of O ...
, the
systematic name A systematic name is a name given in a systematic way to one unique group, organism, object or chemical substance, out of a specific population or collection. Systematic names are usually part of a nomenclature. A semisystematic name or semitrivial ...
s of acyl groups are derived exactly by replacing the -yl suffix of the corresponding
hydrocarbyl In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ex ...
group's systemic name (or the -oic acid suffix of the corresponding carboxylic acid's systemic name) with -oyl, as shown in the table below. The acyls are between the hydrocarbyls and the carboxylic acids. The
hydrocarbyl In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ex ...
group names that end in -yl are not acyl groups, but
alkyl In organic chemistry, an alkyl group is an alkane missing one hydrogen. The term ''alkyl'' is intentionally unspecific to include many possible substitutions. An acyclic alkyl has the general formula of . A cycloalkyl is derived from a cycloa ...
groups derived from alkanes ( methyl, ethyl,
propyl In organic chemistry, propyl is a three-carbon alkyl substituent with chemical formula for the linear form. This substituent form is obtained by removing one hydrogen atom attached to the terminal carbon of propane. A propyl substituent is often ...
,
butyl In organic chemistry, butyl is a four- carbon alkyl radical or substituent group with general chemical formula , derived from either of the two isomers (''n''-butane and isobutane) of butane. The isomer ''n''-butane can connect in two ways, gi ...
), alkenyl groups derived from
alkene In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond. Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, an ...
s (
propenyl In organic chemistry, 1-propenyl (or simply propenyl) has the formula CH=CHCH3 and 2-propenyl (isopropenyl) has the formula CH2=C-CH3. These groups are found in many compounds. Propenyl compounds are isomeric with allyl compounds, which have the ...
, butenyl), or
aryl In organic chemistry, an aryl is any functional group or substituent derived from an aromaticity, aromatic ring, usually an aromatic hydrocarbon, such as phenyl and naphthyl. "Aryl" is used for the sake of abbreviation or generalization, and "Ar ...
groups (
benzyl In organic chemistry, benzyl is the substituent or molecular fragment possessing the structure . Benzyl features a benzene ring () attached to a methylene group () group. Nomenclature In IUPAC nomenclature, the prefix benzyl refers to a substi ...
).


Acyl species

In acyloxy groups the acyl group is bonded to oxygen: R−C(=O)−O−R′ where R−C(=O) is the acyl group. Acylium ions are cations of the type R−C+=O ↔ R−C≡O+ and play an important role as intermediates in organic reactions for example the
Hayashi rearrangement The Hayashi rearrangement is the chemical reaction of ''ortho''-benzoylbenzoic acids catalysis, catalyzed by sulfuric acid or phosphorus pentoxide. This reaction proceeds through electrophilic acylium ion attack with a Spiro compound, spiro inter ...
.


See also

*
Acylation In chemistry, acylation (or alkanoylation) is the chemical reaction in which an acyl group () is added to a compound. The compound providing the acyl group is called the acylating agent. Because they form a strong electrophile when treated with ...
*
Functional group In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the re ...


References


External links

* {{Functional groups Functional groups