Dicarbonyl

Like many alkyldialdehydes, glyoxal is encountered almost exclusively as its hydrate and oligomers thereof.

1,2-Diketones are often generated by oxidation (dehydrogenation) of the diols:[1] 2,3-Butanedione, 2,3-pentanedione, and 2,3-hexanedione are found in small amounts in various foods.

A distinctive feature of 1,2-diketones is the long C-C bond linking the carbonyl groups.

The effect is attributed to repulsion between the partial positive charges of the carbonyl carbon atoms.

[2] 1,2-Diketones condense with many bifunctional nucleophiles, such as urea and thiourea to give heterocycles.

It occurs naturally (as the conjugate base), notably in members of the plant species Oxalis.

Its conjugate base, pyruvate (CH3C(O)CO−2), is a component of the citric acid cycle and product of glucose metabolism (glycolysis).

Instead it is handled almost exclusively as its hydrate, methyl acetal, and oligomers thereof.

[5] Cyclic 1,3-diketones, such as 1,3-cyclohexanedione and dimedone, similarly exist significantly in the enol form.

The conjugate base derived from 1,3-ketones can serve as ligand s to form metal acetylacetonate coordination complexes.

Malonic acid and its esters are the parent members of this class of dicarbonyls.

1,4-Diketones are useful precursors to heterocycles via the Paal–Knorr synthesis, which gives pyrroles: This reactivity is the basis of the neurotoxicity of γ-diketones.

The condensation of 1,4-diketones (and related substrates) with hydrazines afford dihydropyridazines, which can be converted to pyridazines.

Unsaturated members include maleic and fumaric acids and their esters.

Similar hydration and cyclization equilibria apply to maleic dialdehyde,[8][9] glutaraldehyde, and adipaldehyde.

Diacetyl is known to cause the lung disease bronchiolitis obliterans in those individuals exposed to it in an occupational setting.