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In
organic chemistry Organic chemistry is a branch of chemistry that studies the structure, properties and reactions of organic compounds, which contain carbon in covalent bonding.Clayden, J.; Greeves, N. and Warren, S. (2012) ''Organic Chemistry''. Oxford University ...
, a carbonyl group is a
functional group In organic chemistry, a functional group is a substituent or moiety (chemistry), moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions reg ...
composed of a
carbon Carbon (from la, carbo "coal") is a chemical element with the Symbol (chemistry), symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—making four electrons available to form covalent bond, covalent chemical bonds. ...

carbon
atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of atom ...

atom
double-bonded
double-bonded
to an
oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group (periodic table), group in the periodic table, a highly Chemical reaction, reactive nonmetal, and an oxidizing a ...

oxygen
atom: C=O. It is common to several classes of organic compounds, as part of many larger functional groups. A compound containing a carbonyl group is often referred to as a carbonyl compound. The term carbonyl can also refer to
carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom. It is the simplest molecule of the oxocarbon family. In ...

carbon monoxide
as a
ligand In coordination chemistry A coordination complex consists of a central atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by havi ...
in an
inorganic In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they under ...
or
organometallic Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkaline, alkaline earth, and transition metals, and so ...
complex (a
metal carbonyl Metal carbonyls are coordination complexes of transition metals with carbon monoxide 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. Th ...
, e.g.
nickel carbonyl Nickel carbonyl (IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering OrganizationsNational Adhering Organizations in chemistry are the organizations that work as the authorita ...

nickel carbonyl
). The remainder of this article concerns itself with the organic chemistry definition of carbonyl, where carbon and oxygen share a double bond.


Carbonyl compounds

A carbonyl group characterizes the following types of compounds: Other organic carbonyls are
urea Urea, also known as carbamide, is an organic compound with chemical formula CO(NH2)2. This amide has two amidogen, –NH2 groups joined by a carbonyl (C=O) functional group. Urea serves an important role in the metabolism of nitrogen-containing ...

urea
and the
carbamate A carbamate is a category of organic compounds that is formally derived from carbamic acid (NH2COOH). The term includes organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical c ...

carbamate
s, the derivatives of
acyl chloride In organic chemistry, an acyl chloride (or acid chloride) is an organic compound with the functional group -Carbonyl, COChlorine, Cl. Their formula is usually written RCOCl, where R is a side chain. They are reactive derivatives of carboxylic ac ...
s
chloroformate
chloroformate
s and
phosgene Phosgene is the organic chemical compound with the formula In science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific method, builds and Taxonomy (general), organizes knowledge ...

phosgene
,
carbonate ester A carbonate ester (organic carbonate or organocarbonate) is an ester An ester is a chemical compound derived from an acid (organic or inorganic) in which at least one –OH hydroxyl group is replaced by an –O– alkyl (alkoxy) group, as in the s ...

carbonate ester
s,
thioester In chemistry thioesters are compounds with the functional group In organic chemistry, a functional group is a substituent or moiety in a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecul ...

thioester
s,
lactoneLactones are cyclic carboxylic esters, containing a 1-oxacycloalkan-2-one structure (), or analogues having unsaturation or heteroatoms replacing one or more carbon atoms of the ring. Lactones are formed by intramolecular esterification of the co ...

lactone
s,
lactam A lactam is a cyclic amide. The term is a portmanteau of the words '' lactone'' + '' amide''. Nomenclature Greek prefixes in alphabetical order indicate ring size: * α-Lactam (3-atom rings) * β-Lactam (4-atom rings) * γ-Lactam (5-atom ring ...

lactam
s,
hydroxamates
hydroxamates
, and
isocyanate Isocyanate is the functional group with the formula R−N=C=O. Organic compounds that contain an isocyanate group are referred to as isocyanates. An organic compound with two isocyanate groups is known as a diisocyanate. Diisocyanates are manufa ...
s. Examples of inorganic carbonyl compounds are
carbon dioxide Carbon dioxide (chemical formula ) is a colorless gas with a density about 53% higher than that of dry air. Carbon dioxide molecules consist of a carbon atom covalent bond, covalently double bonded to two oxygen atoms. It occurs naturally in At ...

carbon dioxide
and
carbonyl sulfide Carbonyl sulfide is the chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together by ...

carbonyl sulfide
. A special group of carbonyl compounds are 1,3-dicarbonyl compounds that have acidic protons in the central methylene unit. Examples are
Meldrum's acid
Meldrum's acid
,
diethyl malonate Diethyl malonate, also known as DEM, is the diethyl ester An ester is a chemical compound derived from an acid (organic or inorganic) in which at least one –OH hydroxyl group is replaced by an –O– alkyl (alkoxy) group, as in the substitutio ...
and
acetylacetone Acetylacetone is an organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenation, ...

acetylacetone
.


Reactivity


Carbonyl resonance chemistry

Because
oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group (periodic table), group in the periodic table, a highly Chemical reaction, reactive nonmetal, and an oxidizing a ...

oxygen
is more
electronegative Electronegativity, symbolized as ''Chi (letter), χ'', is the tendency of an atom to attract shared electrons (or electron density) to itself. An atom's electronegativity is affected by both its atomic number and the distance at which its valence ...

electronegative
than carbon, carbonyl compounds often have
resonance structures In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they und ...
which affect their reactivity. This relative electronegativity draws electron density away from carbon, increasing the bond's
polarity Polarity may refer to: Science *Polarity (mutual inductance), the relationship between components such as transformer windings *Polarity (projective geometry), in mathematics, a duality of order two *Polarity in embryogenesis, the animal and vegeta ...
, therefore making carbon an
electrophileIn chemistry, an electrophile is a chemical species that forms bonds with Nucleophile, nucleophiles by accepting an electron pair. Because electrophiles accept electrons, they are Lewis acids. Most electrophiles are positively Electric charge, charg ...
(i.e. slightly positive). Carbon can then be attacked by
nucleophiles In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they underg ...
(e.g. negatively charged
ions An ion () is an atom or molecule with a net electric charge, electrical charge. The charge of an electron is considered negative by convention and this charge is equal and opposite to charge of a proton, which is considered positive by convent ...

ions
, like the cyanide ion) or a negatively charged part of another molecule (e.g. the
lone pair In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds composed of atoms, mo ...
electrons of nitrogen in the
ammonia Ammonia is a chemical compound, compound of nitrogen and hydrogen with the chemical formula, formula NH3. A Binary compounds of hydrogen, stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct p ...

ammonia
molecule). During the reaction, the carbon-oxygen
double bond In chemistry, a double bond is a covalent bond between two atoms involving four Electron pair bond, 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 ...
is broken, and the carbonyl group may experience
addition reactionImage:Chlorine addition to ethene.svg, Addition of chlorine to ethylene An addition reaction, in organic chemistry, is in its simplest terms an organic reaction where two or more molecules combine to form a larger one (the adduct).. Addition reacti ...

addition reaction
s. This reaction is known as addition-elimination (because a water molecule is often lost) or
condensation Condensation is the change of the state of matter In physics, a state of matter is one of the distinct forms in which matter can exist. Four states of matter are observable in everyday life: solid, liquid, gas, and Plasma (physics), plasma. ...
. The electronegative oxygen also can react with an electrophile; for example a proton in an acidic solution or with
Lewis acid A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair In chemistry Chemistry is the scientific discipline involved with Ch ...
s to form an
oxocarbenium An oxocarbenium ion (or oxacarbenium ion) is a chemical species characterized by a central sp2-hybridized carbon, an oxygen substituent, and an overall positive charge that is delocalized between the central carbon and oxygen atoms. A oxocarbenium i ...

oxocarbenium
ion. The polarity of oxygen also makes the
alpha hydrogenImage:Alpha and beta positions of benzylacetone-structure.svg, Alpha and beta carbons in the skeletal formula of benzylacetone. The carbonyl has two β-hydrogens and five γ-hydrogens. The alpha carbon (Cα) in organic molecules refers to the first c ...
s of carbonyl compounds ''much'' more acidic (roughly 1030 times more acidic) than typical sp3 C-H bonds, such as those in
methane Methane (, ) is a chemical compound with the chemical formula A chemical formula is a way of presenting information about the chemical proportions of atom An atom is the smallest unit of ordinary matter In classical physics an ...
. For example, the pKa values of
acetaldehyde Ethanal (common name acetaldehyde) is an organic chemical compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds ...
and
acetone Acetone, or propanone, is an organic compound with the chemical formula, formula (methyl group, CH3)2carbonyl, CO. It is the simplest and smallest ketone. It is a colourless, highly volatile and flammable liquid with a characteristic pungent odo ...

acetone
are 16.7 and 19 respectively, while the pKa value of methane is extrapolated to be approximately 50. This is because a carbonyl is in tautomeric
resonance Resonance describes the phenomenon of increased amplitude The amplitude of a Periodic function, periodic Variable (mathematics), variable is a measure of its change in a single Period (mathematics), period (such as frequency, time or Wavelen ...
with an
enol Enols, or more formally, alkenols, are a type of reactive structure or chemical intermediate, intermediate in organic chemistry that is represented as an alkene (olefin) with a hydroxyl group attached to one end of the alkene double bond. The term ...

enol
. The deprotonation of the enol with a strong base produces an
enolate Enolates are organic anions derived from the deprotonation of carbonyl compounds. Rarely isolated, they are widely used as reagents in the synthesis of organic compounds. Bonding and structure Image:Enolate-pi-MOs.png, center, 300px, Molecular or ...

enolate
, which is a powerful nucleophile and can alkylate electrophiles such as other carbonyls. Amides are the most stable of the carbonyl couplings due to their high resonance stabilization between the nitrogen-carbon and carbon-oxygen bonds.


Carbonyl reduction

Carbonyl groups can be reduced by reaction with
hydride In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds composed of atoms, mo ...

hydride
reagents such as
NaBH4
NaBH<sub>4</sub>
and
LiAlH4
LiAlH<sub>4</sub>
, with
baker's yeast '', the yeast commonly used as baker's yeast. Gradation marks are 1 µm apart Baker's yeast is the common name for the strains of yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom (biol ...

baker's yeast
, or by catalytic
hydrogenation Hydrogenation is a chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical A chemical substance is a form of matter having constant ...

hydrogenation
. Ketones give
secondary Secondary is an adjective meaning "second" or "second hand". It may refer to: * Secondary (chemistry), term used in organic chemistry to classify various types of compounds * The group of (usually at least four) defensive backs in gridiron football ...
alcohols while aldehydes, esters and carboxylic acids give
primary Primary or primaries may refer to: Arts, entertainment, and media Music Groups and labels * Primary (band), from Australia * Primary (musician), hip hop musician and record producer from South Korea * Primary Music, Israeli record label Works * ...
alcohols.


Carbonyl alkylation

Carbonyls can be
alkylated Alkylation is the transfer of an alkyl group from one molecule to another. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion or a carbene (or their equivalents). An alkyl group is a piece of a molecule with the ...

alkylated
in
nucleophilic additionIn organic chemistry, a nucleophilic addition reaction is an addition reaction where a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atom ...
reactions using
organometallic Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkaline, alkaline earth, and transition metals, and so ...
compounds such as
organolithiumOrganolithium reagents are organometallic Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkaline, alka ...
reagents,
Grignard reagent A Grignard reagent or Grignard compound is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, ele ...
s, or
acetylideAcetylide refers to chemical compounds with the chemical formulas MC≡CH and MC≡CM, where M is a metal. The term is used loosely and can refer to Substitution reaction#Substituted compounds, substituted acetylides having the general structure RC ...

acetylide
s. Carbonyls also may be alkylated by
enolate Enolates are organic anions derived from the deprotonation of carbonyl compounds. Rarely isolated, they are widely used as reagents in the synthesis of organic compounds. Bonding and structure Image:Enolate-pi-MOs.png, center, 300px, Molecular or ...

enolate
s as in
aldol reaction The aldol reaction is a means of forming carbon–carbon bonds in organic chemistry. Discovered independently by the Russian chemist Alexander Borodin in 1869 and by the French chemist Charles-Adolphe Wurtz in 1872, the reaction combines two carbon ...

aldol reaction
s. Carbonyls are also the prototypical groups with
vinylogousVinylogy is the transmission of electronic effects through a conjugated organic bonding system. The concept was introduced in 1926 by Ludwig Claisen to explain the acidic properties of formylacetone and related ketoaldehydes. Its adjectival form, ...

vinylogous
reactivity (e.g. the
Michael reaction The Michael reaction or Michael addition is the nucleophilic addition of a carbanion or another nucleophile to an α,β-unsaturated carbonyl compound containing an electron withdrawing group. It belongs to the larger class of conjugate additions. Th ...

Michael reaction
where an unsaturated carbon in
conjugation Conjugation or conjugate may refer to: Linguistics * Grammatical conjugation, the modification of a verb from its basic form * Emotive conjugation or Russell's conjugation, the use of loaded language Mathematics * Complex conjugation, the change ...
with the carbonyl is alkylated instead of the carbonyl itself).


Carbonyl chemoselectivity

In case of multiple carbonyl types in one molecule, one can expect the most electrophilic carbonyl carbon to react first.
Acyl chloride In organic chemistry, an acyl chloride (or acid chloride) is an organic compound with the functional group -Carbonyl, COChlorine, Cl. Their formula is usually written RCOCl, where R is a side chain. They are reactive derivatives of carboxylic ac ...
s and
carboxylic anhydride An organic acid anhydride is an acid anhydride that is an organic compound. An acid anhydride is a compound that has two acyl groups chemical bond, bonded to the same oxygen atom. A common type of organic acid anhydride is a carboxylic anhydride, ...
s react fastest, followed by
aldehyde Chemically, an aldehyde is a compound containing a functional group In organic chemistry, a functional group is a substituent or moiety (chemistry), moiety in a molecule that causes the molecule's characteristic chemical reactions. The same fu ...

aldehyde
s and
ketone In chemistry, a ketone is a functional group with the structure R2C=O, where R can be a variety of carbon-containing substituents. Ketones contain a carbonyl group (a carbon-oxygen double bond). The simplest ketone is acetone (R = R' = methyl) ...
s.
Ester An ester is a chemical compound derived from an acid (organic or inorganic) in which at least one –OH hydroxyl group is replaced by an –O– alkyl (alkoxy) group, as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ...

Ester
s react much more slowly and
amide In organic chemistry Organic chemistry is a branch of chemistry that studies the structure, properties and reactions of organic compounds, which contain carbon in covalent bonding.Clayden, J.; Greeves, N. and Warren, S. (2012) ''Organic Chem ...

amide
s are almost completely unreactive due to resonance of the amide nitrogen towards the carbonyl group. This reactivity difference allows
chemoselectivityChemoselectivity is the preferential outcome of a chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical A chemical substance is a form ...

chemoselectivity
when a reactant contains multiple carbonyl groups. An instructive example is found in the last part of the
total synthesis Total synthesis is the complete chemical synthesis As a topic of chemistry, chemical synthesis (or combination) is the artificial execution of chemical reactions to obtain one or several product (chemistry), products. This occurs by physics, phy ...
of
monensin Monensin is a polyether Ethers are a class of organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbo ...

monensin
by Kishi in 1979: The left-hand reactant possesses two potential electrophilic sites: an aldehyde (indicated in blue) and an ester (indicated in green). Only the aldehyde, which is more electrophilic, will react with the enolate of the methyl ketone in the other part of the molecule. The methyl ester remains untouched. Of course, other effects can play a role in this selectivity process, including electronic effects, steric effects, and
thermodynamic versus kinetic reaction control Thermodynamic reaction control or kinetic reaction control in a chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical A chemical subs ...
.


Carbonyl specialty reactions

Other important reactions include: * Carbonyl alpha-substitution reactions *
Wittig Reaction The Wittig reaction or Wittig olefination is a chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical A chemical substance is a form ...

Wittig Reaction
a phosphonium ylid is used to create an alkene *
Wolff-Kishner reduction
Wolff-Kishner reduction
into a
hydrazone Hydrazones are a class of organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenati ...
and further into a saturated alkane *
Clemmensen reduction Clemmensen reduction is a chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical A chemical substance is a form of matter having const ...
into a saturated alkane * Mozingo reduction into a saturated alkane * Conversion into thioacetals * Hydration reaction, Hydration to hemiacetals and hemiketals, and then to acetals and ketals * Reaction with
ammonia Ammonia is a chemical compound, compound of nitrogen and hydrogen with the chemical formula, formula NH3. A Binary compounds of hydrogen, stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct p ...

ammonia
and primary amines to form imines * Reaction with hydroxylamines to form oximes * Reaction with cyanide anion to form cyanohydrins * Oxidation with oxaziridines to Acyloin#Enolate oxidation by sulfonyloxazirines, acyloins * Reaction with Tebbe's reagent and phosphonium ylides to alkenes. * Perkin reaction, an
aldol reaction The aldol reaction is a means of forming carbon–carbon bonds in organic chemistry. Discovered independently by the Russian chemist Alexander Borodin in 1869 and by the French chemist Charles-Adolphe Wurtz in 1872, the reaction combines two carbon ...

aldol reaction
variant * Aldol condensation, a reaction between an enolate and a carbonyl * Cannizzaro reaction, a disproportionation of aldehydes into alcohols and acids * Tishchenko reaction, another disproportionation of aldehydes that gives a dimeric ester * Nucleophilic abstraction is used to produce carbon dioxide


Spectroscopy

* Infrared spectroscopy: the C=O double bond absorbs infrared light at wavenumbers between approximately 1600–1900 cm−1(5263 nm to 6250 nm). The exact location of the absorption is well understood with respect to the geometry of the molecule. This absorption is known as the "carbonyl stretch" when displayed on an infrared absorption spectrum. In addition, the ultraviolet-visible spectra of propanone in water gives an absorption of carbonyl at 257 nm. * Nuclear magnetic resonance: the C=O double-bond exhibits different resonances depending on surrounding atoms, generally a downfield shift. The 13C NMR of a carbonyl carbon is in the range of 160–220 ppm.


See also

* Organic chemistry * Functional group * Bridging carbonyl * Electrophilic addition


References


Further reading

* L.G. Wade, Jr. ''Organic Chemistry, 5th ed.'' Prentice Hall, 2002. * The Frostburg State University Chemistry Department
Organic Chemistry Help
(2000). * Advanced Chemistry Development, Inc
IUPAC Nomenclature of Organic Chemistry
(1997). * William Reusch. tar

(2004). * Purdue Chemistry Departmen

(retrieved Sep 2006). Includes water solubility data. * William Reusch. (2004

Retrieved 23 May 2005. * ILPI. (2005

{{Authority control Carbonyl compounds, Functional groups