The wordketone is derived fromAketon, an old German word foracetone.[2][3]
According to the rules ofIUPAC nomenclature, ketone names are derived by changing thesuffix-ane of the parentalkane to-anone. Typically, the position of the carbonyl group is denoted by a number, but traditional nonsystematic names are still generally used for the most important ketones, for exampleacetone andbenzophenone. These nonsystematic names are considered retained IUPAC names,[4] although some introductory chemistry textbooks use systematic names such as "2-propanone" or "propan-2-one" for the simplest ketone (CH3−C(=O)−CH3) instead of "acetone".
The derived names of ketones are obtained by writing separately the names of the twoalkyl groups attached to the carbonyl group, followed by "ketone" as a separate word. Traditionally the names of the alkyl groups were written in order of increasing complexity, for example methyl ethyl ketone. However, according to the rules ofIUPAC nomenclature, the alkyl groups are written alphabetically, for example ethyl methyl ketone. When the two alkyl groups are the same, the prefix "di-" is added before the name of alkyl group. The positions of other groups are indicated byGreek letters, the α-carbon being the atom adjacent to carbonyl group.
Although used infrequently,oxo is theIUPAC nomenclature for the oxo group (=O) and used as prefix when the ketone does not have the highest priority. Other prefixes, however, are also used. For some common chemicals (mainly in biochemistry),keto refer to the ketonefunctional group.
The ketone carbon is often described assp2 hybridized, a description that includes both their electronic and molecular structure. Ketones aretrigonal planar around the ketonic carbon, with C–C–O and C–C–C bond angles of approximately 120°. Ketones differ fromaldehydes in that the carbonyl group (C=O) is bonded to two carbons within acarbon skeleton. In aldehydes, the carbonyl is bonded to one carbon and one hydrogen and are located at the ends of carbon chains. Ketones are also distinct from other carbonyl-containingfunctional groups, such ascarboxylic acids,esters andamides.[5]
The carbonyl group ispolar because the electronegativity of the oxygen is greater than that for carbon. Thus, ketones arenucleophilic at oxygen andelectrophilic at carbon. Because the carbonyl group interacts with water byhydrogen bonding, ketones are typically more soluble in water than the related methylene compounds. Ketones are hydrogen-bond acceptors. Ketones are not usually hydrogen-bond donors and cannot hydrogen-bond to themselves. Because of their inability to serve both as hydrogen-bond donors and acceptors, ketones tend not to "self-associate" and are more volatile than alcohols andcarboxylic acids of comparablemolecular weights. These factors relate to the pervasiveness of ketones in perfumery and as solvents.
Ketones are classified on the basis of their substituents. One broad classification subdivides ketones into symmetrical and unsymmetrical derivatives, depending on the equivalency of the two organic substituents attached to the carbonyl center. Acetone andbenzophenone ((C6H5)2CO) are symmetrical ketones.Acetophenone(C6H5C(O)CH3) is an unsymmetrical ketone.
Many kinds of diketones are known, some with unusual properties. The simplest isdiacetyl(CH3C(O)C(O)CH3), once used as butter-flavoring inpopcorn.Acetylacetone (pentane-2,4-dione) is virtually a misnomer (inappropriate name) because this species exists mainly as the monoenolCH3C(O)CH=C(OH)CH3. Its enolate is a common ligand incoordination chemistry.
Many ketones are cyclic. The simplest class have the formula(CH2)nCO, wheren varies from 2 forcyclopropanone ((CH2)2CO) to the tens. Larger derivatives exist.Cyclohexanone ((CH2)5CO), a symmetrical cyclic ketone, is an important intermediate in the production ofnylon.Isophorone, derived from acetone, is an unsaturated, asymmetrical ketone that is the precursor to otherpolymers.Muscone, 3-methylpentadecanone, is an animalpheromone. Another cyclic ketone iscyclobutanone, having the formula(CH2)3CO.
An aldehyde differs from a ketone in that it has a hydrogen atom attached to its carbonyl group, making aldehydes easier to oxidize. Ketones do not have a hydrogen atom bonded to the carbonyl group, and are therefore more resistant to oxidation. They areoxidized only by powerfuloxidizing agents which have the ability tocleave carbon–carbon bonds.
Ketones (and aldehydes) absorb strongly in theinfra-red spectrum near 1750cm−1, which is assigned to νC=O ("carbonyl stretching frequency"). The energy of the peak is lower for aryl and unsaturated ketones.[6]
Whereas1H NMRspectroscopy is generally not useful for establishing the presence of a ketone,13C NMR spectra exhibit signals somewhat downfield of 200ppm depending on structure. Such signals are typically weak due to the absence ofnuclear Overhauser effects. Since aldehydes resonate at similarchemical shifts, multiple resonance experiments are employed to definitively distinguish aldehydes and ketones.
"Methyl ketone" redirects here. For the specific compound, seeacetone. For the functional group, seeacetyl.
Ketones give positive results inBrady's test, the reaction with 2,4-dinitrophenylhydrazine to give the corresponding hydrazone. Ketones may be distinguished from aldehydes by giving a negative result withTollens' reagent or withFehling's solution. Methyl ketones give positive results for theiodoform test.[7] Ketones also give positive results when treated withm-dinitrobenzene in presence of dilute sodium hydroxide to give violet coloration.
Many methods exist for the preparation of ketones in industrial scale and academic laboratories. Ketones are also produced in various ways by organisms; see the section on biochemistry below.
Byhydration ofalkynes.[10] Such processes occur viaenols and require the presence of an acid andmercury(II) sulfate (HgSO4). Subsequent enol–keto tautomerization gives a ketone. This reaction always produces a ketone, even with a terminal alkyne, the only exception being the hydration ofacetylene, which producesacetaldehyde.
FromWeinreb amides using stoichiometric organometallic reagents.
Keto-enol tautomerism.1 is the keto form;2 is the enol.
Ketones that have at least onealpha-hydrogen, undergoketo-enol tautomerization; the tautomer is anenol. Tautomerization iscatalyzed by both acids and bases. Usually, the keto form is more stable than the enol. This equilibrium allows ketones to be prepared via thehydration ofalkynes.
C−H bonds adjacent to the carbonyl in ketones are more acidicpKa ≈ 20) than theC−H bonds in alkane (pKa ≈ 50). This difference reflects resonance stabilization of theenolate ion that is formed upondeprotonation. The relative acidity of the α-hydrogen is important in the enolization reactions of ketones and other carbonyl compounds. The acidity of the α-hydrogen also allows ketones and other carbonyl compounds to react as nucleophiles at that position, with eitherstoichiometric and catalytic base. Using very strong bases like lithium diisopropylamide (LDA, pKa of conjugate acid ~36) under non-equilibrating conditions (–78 °C, 1.1 equiv LDA in THF, ketone added to base), the less-substitutedkineticenolate is generated selectively, while conditions that allow for equilibration (higher temperature, base added to ketone, using weak or insoluble bases, e.g.,CH3CH2ONa inCH3CH2OH, orNaH) provides the more-substitutedthermodynamic enolate.
Ketones are also weak bases, undergoingprotonation on the carbonyl oxygen in the presence ofBrønsted acids. Ketonium ions (i.e., protonated ketones) are strong acids, with pKa values estimated to be somewhere between –5 and –7.[19][20] Although acids encountered in organic chemistry are seldom strong enough to fully protonate ketones, the formation of equilibrium concentrations of protonated ketones is nevertheless an important step in the mechanisms of many common organic reactions, like the formation of an acetal, for example. Acids as weak as pyridinium cation (as found in pyridinium tosylate) with a pKa of 5.2 are able to serve as catalysts in this context, despite the highly unfavorable equilibrium constant for protonation (Keq < 10−10).
An important set of reactions follow from the susceptibility of the carbonyl carbon towardnucleophilic addition and the tendency for the enolates to add to electrophiles.Nucleophilic additions include in approximate order of their generality:[8]
With water (hydration) givesgeminal diols, which are usually not formed in appreciable (or observable) amounts
With an alcohols oralkoxides to gives thehemiketal or its conjugate base. With adiol to theketal. This reaction is employed to protect ketones.
Withsodium amide resulting in C–C bond cleavage with formation of the amide RCONH2 and the alkane or arene R'H, a reaction called the Haller–Bauer reaction.[21]
Ketones are cleaved by strong oxidizing agents and at elevated temperatures. Their oxidation involves carbon–carbon bond cleavage to afford a mixture of carboxylic acids having lesser number of carbon atoms than the parent ketone.
Ketones do not appear in standardamino acids, nucleic acids, nor lipids. The formation of organic compounds inphotosynthesis occurs via the ketoneribulose-1,5-bisphosphate. Many sugars are ketones, known collectively asketoses. The best known ketose isfructose; it mostly exists as a cyclichemiketal, which masks the ketone functional group.Fatty acid synthesis proceeds via ketones.Acetoacetate is an intermediate in theKrebs cycle which releases energy from sugars and carbohydrates.[22]
Ketones are produced on massive scales in industry as solvents, polymer precursors, and pharmaceuticals. In terms of scale, the most important ketones areacetone,methylethyl ketone, andcyclohexanone.[23] They are also common in biochemistry, but less so than in organic chemistry in general. Thecombustion of hydrocarbons is an uncontrolled oxidation process that gives ketones as well as many other types of compounds.
Although it is difficult to generalize on thetoxicity of such a broad class of compounds, simple ketones are, in general, not highly toxic. This characteristic is one reason for their popularity as solvents. Exceptions to this rule are theunsaturated ketones such asmethyl vinyl ketone withLD50 of 7 mg/kg (oral).[23]
^The word "ketone" was coined in 1848 by the German chemistLeopold Gmelin. See: Leopold Gmelin, ed.,Handbuch der organischen Chemie: Organische Chemie im Allgemeinen … (Handbook of organic chemistry: Organic chemistry in general … ), 4th ed., (Heidelberg, (Germany): Karl Winter, 1848), volume 1, p. 40. From page 40:"Zu diesen Syndesmiden scheinen auch diejenigen Verbindungen zu gehören, die alsAcetone im Allegemeinen (Ketone?) bezeichnet werden." (To these syndesmides*, those compounds also seem to belong, which are designated asacetones in general (ketones?).") [*Note: In 1844, the French chemistAuguste Laurent suggested a new nomenclature for organic compounds. One of his new classes of compounds was "syndesmides", which were compounds formed by the combination of two or more simpler organic molecules (from the Greek σύνδεσμος (syndesmos, union) +-ide (indicating a group of related compounds)). For example, acetone could be formed by the dry distillation of metal acetates, so acetone was the syndesmide of two acetate ions. See: Laurent, Auguste (1844)"Classification chimique,"Comptes rendus,19 : 1089–1100; see especially p. 1097.
^Smith, Brian (November 2018)."The C=O Bond, Part VIII: Review".Spectroscopy. November 2018.33:24–29.Archived from the original on 13 February 2024. Retrieved12 February 2024.
^Mendham, J.; Denney, R. C.; Barnes, J. D.; Thomas, M. J. K. (2000).Vogel's Quantitative Chemical Analysis (6th ed.). New York: Prentice Hall.ISBN0-582-22628-7.
^Nelson, D. L.; Cox, M. M. (2000)Lehninger, Principles of Biochemistry. 3rd Ed. Worth Publishing: New York.ISBN1-57259-153-6.
^abSiegel, Hardo; Eggersdorfer, Manfred (2000). "Ketones".Ullmann's Encyclopedia of Industrial Chemistry.doi:10.1002/14356007.a15077 (inactive 12 July 2025).ISBN9783527306732.{{cite book}}: CS1 maint: DOI inactive as of July 2025 (link)
