carbonyl

(noun)

a divalent functional group (-CO-), characteristic of aldehydes, ketones, carboxylic acids, amides, carboxylic acid anhydrides, carbonyl halides, esters, and others.

Related Terms

Examples of carbonyl in the following topics:

  • Related Carbonyl Derivatives

    • Other functional group combinations with the carbonyl group can be prepared from carboxylic acids, and are usually treated as related derivatives.
    • Although nitriles do not have a carbonyl group, they are included here because the functional carbon atoms all have the same oxidation state.
    • The Greek letter locates the nitrogen relative to the carbonyl group of the amide.

  • Properties of Aldehydes and Ketones

    • Because of the greater electronegativity of oxygen, the carbonyl group is polar, and aldehydes and ketones have larger molecular dipole moments (D) than do alkenes.
    • The polarity of the carbonyl group also has a profound effect on its chemical reactivity, compared with the non-polar double bonds of alkenes.
    • The C=O bond energy of a carbonyl group, on the other hand, varies with its location, as follows:
    • This suggests that addition reactions to carbonyl groups should be thermodynamically disfavored, as is the case for the addition of water.
    • Proof that rapid and reversible addition of water to carbonyl compounds occurs is provided by experiments using isotopically labeled water.

  • Addition to Carbonyl Double Bonds

    • Stereoelectronic factors influence the addition of nucleophilic reagents to carbonyl groups, particularly aldehydes and ketones.
    • Selective reduction of 4-tert-butylcyclohexanone (I) to a 10:1 mixture of trans- and cis-4-tert-butylcyclohexanol by LiAlH4 is an example of diastereoselectivity, reflecting a preference for hydride attack at the more hindered axial face of the carbonyl group.
    • In compound II the exo face of the prochiral carbonyl group is less hindered than the endo face.

  • Nomenclature of Aldehydes and Ketones

    • Aldehydes and ketones are organic compounds which incorporate a carbonyl functional group, C=O.
    • Chain numbering normally starts from the end nearest the carbonyl group.
    • In cyclic ketones the carbonyl group is assigned position #1, and this number is not cited in the name, unless more than one carbonyl group is present.
    • In common names carbon atoms near the carbonyl group are often designated by Greek letters.
    • Simple substituents incorporating a carbonyl group are often encountered.

  • Irreversible Addition Reactions

    • Most hydrates and hemiacetals (Y = OH & OR), for example, are known to decompose spontaneously to the corresponding carbonyl compounds.
    • In all these cases addition of H–Y to carbonyl groups is clearly reversible.
    • The last reaction shows how an acetal derivative may be used to prevent reduction of a carbonyl function (in this case a ketone).
    • Because of their ring strain, epoxides undergo many carbonyl-like reactions, as noted previously.
    • Two additional examples of the addition of organometallic reagents to carbonyl compounds are informative.

  • Polar Functions and Umpolung

    • This is demonstrated in the following diagram, where the customary reactivity of a carbonyl substrate is shown on the left.
    • Subsequent removal of the oxygen protective group exposes the cyanohydrin which immediately decomposes to a carbonyl group.
    • Reaction 3 illustrates the use of nitro alkanes as latent carbonyl groups.
    • The final step, in which an aci-anion is hydrolyzed to a carbonyl group, is called the Nef reaction.
    • The example in equation 4 is a variant of this tactic, wherein an isonitrile assumes the role of a carbonyl anion.

  • Reduction

    • Other useful reductions of carbonyl compounds, either to alcohols or to hydrocarbons, may take place by different mechanisms.
    • The reductive conversion of a carbonyl group to a methylene group requires complete removal of the oxygen, and is called deoxygenation.
    • The second example illustrates the lability of functional substituents alpha to the carbonyl group.
    • In contrast to the previous two procedures, this method of carbonyl deoxygenation requires two separate steps.
    • The bicyclic compound shown here has two carbonyl groups, one of which is sterically hindered (circled in orange).

  • Aldehydes and Ketones

    • Aldehydes and ketones are classes of organic compounds that contain a carbonyl (C=O) group.
    • In organic chemistry, a carbonyl group is a functional group which has a carbon double bonded to an oxygen atom: C=O.
    • When a carbonyl functional group is placed within a molecule, it is known as a ketone.
    • A ketone is a type of organic compound where a carbonyl group bonds to two other carbon atoms of the carbon backbone.
    • An aldehyde is characterized by the presence of a carbonyl functional group at the end of a compound's carbon skeleton.

  • Reversible Addition Reactions

    • It has been demonstrated (above) that water adds rapidly to the carbonyl function of aldehydes and ketones.
    • Some of these reagents are listed in the following table, together with the structures and names of their carbonyl reaction products.
    • An interesting aspect of these carbonyl derivatives is that stereoisomers are possible when the R-groups of the carbonyl reactant are different.
    • The other is amide-like and is deactivated by the adjacent carbonyl group.
    • Consequently, enamines are easily converted back to their carbonyl precursors by acid-catalyzed hydrolysis.

  • Esters

    • Esters contain a carbonyl center, which gives rise to 120 degree C-C-O and O-C-O bond angles due to sp2 hybridization.
    • This peak changes depending on the functional groups attached to the carbonyl.
    • Esters react with nucleophiles at the carbonyl carbon.
    • The C-H bonds adjacent to the carbonyl are weakly acidic, but undergo deprotonation with strong bases.
    • The carbonyl oxygen is weakly basic (less so than in amides), but can form adducts with Lewis acids.