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General structure of 1,2-, 1,3-, and 1,4-dicarbonyls. In organic chemistry, a dicarbonyl is a molecule containing two carbonyl (C=O) groups.Although this term could refer to any organic compound containing two carbonyl groups, it is used more specifically to describe molecules in which both carbonyls are in close enough proximity that their reactivity is changed, such as 1,2-, 1,3-, and 1,4 ...
Many carbonyl compounds exhibit keto–enol tautomerism. This effect is especially pronounced in 1,3-dicarbonyl compounds that can form hydrogen-bonded enols. The equilibrium constant is dependent upon the solvent polarity, with the cis-enol form predominating at low polarity and the diketo form predominating at high polarity.
Interactions between carbonyl groups and other substituents were found in a study of collagen. [3] Substituents can affect carbonyl groups by addition or subtraction of electron density by means of a sigma bond. [4] ΔHσ values are much greater when the substituents on the carbonyl group are more electronegative than carbon. [4] A carbonyl ...
Acidity of diethyl malonate, a 1,3-dicarbonyl compound. The central carbon in 1,3-dicarbonyl compound is known as an activated methylene group. This is because, owing to the structure, the carbon is especially acidic and can easily be deprotonated to form a methylene group. [4]
One of the principal uses of this compound is in the malonic ester synthesis. The carbanion (2) formed by reacting diethyl malonate (1) with a suitable base can be alkylated with a suitable electrophile. This alkylated 1,3-dicarbonyl compound (3) readily undergoes decarboxylation with loss of carbon dioxide, to give a substituted acetic acid (4):
Some authors have broadened the definition of the Michael addition to essentially refer to any 1,4-addition reaction of α,β-unsaturated carbonyl compounds. Others, however, insist that such a usage is an abuse of terminology, and limit the Michael addition to the formation of carbon–carbon bonds through the addition of carbon nucleophiles.
The desired pathway toward the Stetter product is the 1,4-addition of the nucleophilic aldehyde to a Michael-type acceptor. After 1,4-addition, the reaction is irreversible and ultimately, the 1,4-dicarbonyl is formed when the catalyst is kicked out to regenerate CN − or the thiazolium ylide. Scheme 3. Mechanism of the Stetter reaction
It can be summarised by the formula (CO) 3 Co(μ-CO) 2 Co(CO) 3 and has C 2v symmetry. This structure resembles diiron nonacarbonyl (Fe 2 (CO) 9) but with one fewer bridging carbonyl. The Co–Co distance is 2.52 Å, and the Co–CO terminal and Co–CO bridge distances are 1.80 and 1.90 Å, respectively. [8]