The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



organic compounds with a hydroxyl group OH at a carbon-carbon double bond. The simplest enol is vinyl alcohol CH2=CHOH, which like most enols is unstable in the free state and changes into its isomer acetaldehyde:

The instability of enols is due to their being in tautomeric equilibrium with the corresponding carbonyl compounds:

Since the carbonyl form is energetically favored over the enol one by 54–71 kilojoules/mole (13–17 kcal/mole), equilibrium is usually displaced in the direction of formation of aldehydes and ketones. Thus acetone contains 2.5 x 10−4 percent enol and cyclohexanone 2.5 x 10−2 percent enol. However, in some cases the enol form is stable (for example, with β-diketones, β-ketoaldehydes, and cyclic α-diketones), because the energy difference is offset by energy gain owing to formation of a system of conjugated double bonds, as well as of a hydrogen bond owing to hydroxyl group formation. The enol content of an equilibrium mixture also depends on the solvent, temperature, and other factors.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
The product of this reaction is known as Ruhemann's purple (Rp) [3-4].The literature review shows that study of reactions of ninhydrin is a subject of more interest and some of the useful reactions such as amidoalkylation[5], Knoevenagel condensation [6], oxidation [7,8], reduction [9,10], reaction with enols and aromatic compounds [11], synthesis of heterocyclic compounds [12], Friedel-Crafts type reaction [13-16], Kolbe-Schmitt [17], Passerini [18], Wittig [19] and Morita-Baylis-Hillman [20] have been investigated in this area.
Pramanik, Facile Acid-Catalyzed Condensation of Ninhydrin with Enols and Aromatic Compounds and Microwave Enhanced Condensation of Ninhydrin with Hydroxy Aromatic Systems in Solid State, Indian J.
At first glance, the reaction parameters obtained from our computational approach, at 6-31g(d) level (but also at 6-311++g(3d,3p) vide infra), calculated along the lines used for aldol reaction of acetone by Zhang and Houk [26], that is, the reaction of tropinone and granatanone enols with benzaldehyde, totally disagreed with experiment.
As such reactions had no precedents in the literature, we approached the problem by comparing experimental results with data obtained in a theoretical manner, analogous to the one used by Houk for acetone reaction and invoking ketone enol [26].
The chemicals that are produced at this point are flavor volatiles that include chemical compounds, such as alcohols, furans and enols, that contribute more and more to the overall caramel-like profile.
Sandia said the compounds, known as enols, were discovered using a new flame chemistry probe operated at the Advanced Light Source at Lawrence Berkeley National Laboratory.
Sandia noted that, the enols were discovered when the team was looking for signatures of different isomers in flames.
Enols are important reactive intermediates in organic chemistry.
In all these cases the phosphoryl forms are at least by 10 kcal/mol more stable than the corresponding enols. The most enolizing substituents appear to be the nitro and trifluoromethylsulphonyl groups, with very close enolizing power.
However, very little is known about possible enol forms of the phosphoryl group.
Steel, "Transition metal-catalysed cross-coupling reactions of P-activated enols," Chemical Society Reviews, vol.
The recorded bands were present at 32003450 cm-1 due to presence of OH and peaks near 17101730 for CO ester 15301650 for CO of enols 14201430 cm-1 for CH; and 10501150 cm-1 for of CO [7].