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The term enol is an abbreviation of alkenol, a portmanteau deriving from "-ene"/"alkene" and the "-ol". Many kinds of enols are known. [1] Keto–enol tautomerism refers to a chemical equilibrium between a "keto" form (a carbonyl, named for the common ketone case) and an enol.
The keto and enol tautomers of acetylacetone coexist in solution. The enol form has C 2v symmetry, meaning the hydrogen atom is shared equally between the two oxygen atoms. [4] In the gas phase, the equilibrium constant, K keto→enol, is 11.7, favoring the enol form.
Some examples of tautomers Keto-enol tautomerization typically strongly favors the keto tautomer, but an important exception is the case of 1,3-diketones such as acetylacetone. [6] Tautomerization is pervasive in organic chemistry.
The compound exists mainly as the enol tautomer. [2] Synthesis, structure, and reactivity. 1,3-Cyclohexanedione is produced by semi-hydrogenation of resorcinol: [3] [4]
The tautomerization can also be catalyzed via photochemical process. These findings suggest that the keto–enol tautomerization is a viable route under atmospheric and stratospheric conditions, relevant to a role for vinyl alcohol in the production of organic acids in the atmosphere. [5] [6]
Keto-enol tautomerism. 1 is the keto form; 2 is the enol. Ketones that have at least one alpha-hydrogen, undergo keto-enol tautomerization; the tautomer is an enol. Tautomerization is catalyzed by both acids and bases. Usually, the keto form is more stable than the enol. This equilibrium allows ketones to be prepared via the hydration of alkynes.
Ethyl acetoacetate is subject to keto-enol tautomerism. In the neat liquid at 33 °C, the enol consists of 15% of the total. [5] The enol is moderately acidic. Thus ethyl acetoacetate behaves similarly to acetylacetone: [6] CH 3 C(O)CH 2 CO 2 C 2 H 5 + NaH → CH 3 C(O)CHNaCO 2 C 2 H 5 + H 2. The resulting carbanion undergoes nucleophilic ...
These structures exhibit tautomerism to give thioketones or thioaldehydes, analogous to keto–enol tautomerism of carbonyl structures. [1] References