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Ketones - important compounds in organic chemistry


Ketones are chemical compounds that contain a non-terminal carbonyl group (>C=O) as a functional group. Each ketone group [C-C(O)-C] contains three carbon atoms. All ketones contain at least three carbon atoms. The smallest ketone by molecule is the well-known solvent acetone.
In contrast to the aldehydes, here the carbonyl carbon is connected to carbon atoms in both bonding directions. Ketones can be regarded as oxidation products of secondary alcohols. Ketones that can be derived from alkanes are called alkanones, and ketones that can be derived from alkenes or alkynes are called alkenones or alkynones.

As mentioned at the beginning, the simplest aliphatic ketone is acetone. A simple aromatic ketone is benzophenone (diphenyl ketone). A mixed ketone is acetophenone (methylphenylketone). Certain ketones are also physiologically formed as a metabolic product in the liver.



According to the IUPAC nomenclature, ketones are given the suffix -on if the carbonyl group is the highest priority group contained in the molecule. Accordingly, the ketone derived from propane is called propanone (CH3-CO-CH3, trivial name: acetone). In ketones with more than three carbon atoms, the carbonyl group is located in the parent chain and is given the smallest possible number, which can either be placed before the name or, in the case of more complicated molecules, inevitably directly before the suffix -on. For example: CH3-CH2-CH2-CO-CH3 is called 2-pentanone or pentan-2-one. If the carbonyl group does not have the highest priority, the prefix oxo- is used. For example, CH3-CO-CH2-CHO is called 3-oxobutanal.
Often, however, various ketones have names consisting of the designation of the alkyl residues followed by the suffix -ketone. For example, butanone is also called methyl ethyl ketone (MEK). If one of the substituents is a phenyl group, the ending -phenone is common, as for example in acetophenone.



Ketones (low molecular weight) are colourless, polar liquids, i.e. easily soluble in water, and are characterised by pleasant, fruity odours. Higher-molecular ketones are solids.
Ketones are generally less reactive than aldehydes and do not tend to polymerise.



Friedel-Crafts acylation is considered the most important production method for aromatic ketones.
Other production methods:

  • By oxidation of secondary alcohols.
  • By ozonolysis of alkenes.
  • Ketone synthesis by Gilman and van Ess - here, the analogous ketone is obtained from a carboxylic acid (R1+1) and a lithium alkyl compound (R2) by hydrolysis.
  • Reaction of Weinreb amides with alkyl-lithium compounds and subsequent aqueous-acidic work-up.
  • Phenol synthesis by the cumene hydroperoxide process (Hock process) with acetone as product.
  • Water addition to alkynes.  



Aldehydes and ketones can be reduced by many reducing agents. The reaction products are the corresponding alcohols. Since the aldehyde group is always terminal, primary alcohols are always formed from aldehydes by reduction. In contrast, secondary alcohols are always formed from ketones. Aldehydes and ketones can also be produced by reversing this reaction, i.e. by oxidising primary or secondary alcohols. However, in contrast to aldehydes, ketones are very difficult to oxidise. In this process, a bond between a carbonyl carbon and an adjacent carbon is cleaved. The resulting molecular fragments are carboxylic acids.


Important ketones

  • Acetone, cyclohexanone
  • Raspberry ketone, mycosporine
  • Butinone, the simplest representative of the ketones with an additional C≡C triple bond.


Use of ketones

  • Acetone: solvent, cleaning agent
  • Methyl ethyl ketone (butanone): Solvent; synthesis auxiliary
  • Methyl isobutyl ketone: Solvent
  • Cyclohexanone: Solvent; production of perlon
  • Raspberry ketone: flavouring of food (smell of raspberries)


Spectroscopy of ketones

In IR spectra of ketones and aldehydes, the characteristic band of the C=O valence vibration is found in the range from 1690 to 1750 cm-1.

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Related links/Sources:
Lernhelfer.de Stand 10.01.2023
Chemie.de Stand 10.01.2023



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