A proton and 13C NMR study of keto-enol tautomerism of some β-ketoamides (2023)

Quoted by (7)

  • The applications of β-ketoamides for the synthesis of heterocycles

    2022, Journal of Heterocyclic Chemistry

    bKetoamides possess multiple nucleophilic and electrophilic reaction sites within their molecular structures, which makes them excellent building blocks for the construction of various heterocyclic compounds. In this review, we summarize the applications of structurally diverse structuresb-ketoamides for the synthesis of (1) Five-membered heterocycles, including furans, thiophenes, pyrroles, indoles, pyrazoles, triazoles and their derivatives; (2) six-membered nitrogen and oxygen-containing heterocycles such as pyridones, dihydropyridines, pyridines, quinolones, quinolines, pyranones and the like; (3) several lactams and some aza-aliphatic rings. The focus is on multicomponent reactions that take advantage of the unique and versatile reactivities ofb-ketoamide.

  • Polyaromatic ring containing β-diketone derivatives with antiproliferative activity in human breast cancer cell lines: Synthesis, structure, DNA binding and molecular docking

    2022, Journal of Molecular Structure

    Quote Excerpt:

    The vinylic proton signal characterizes keto-enol tautomerism in diketone derivatives [22]. The secondary amine proton –NH of L1 signals at 12.9 ppm (the acidic proton signal for the enol form is 15.3 ppm) confirms the ketamine form in solution [23]. The primary amino protons of L1 produce the signal at 3.6 ppm, confirming the condensation of only one -NH2 group of ODA with the keto group of DBM.

    Plant β-diketone derivatives exhibit biological activity due to tautomerism and extended conjugation with the aromatic ring system. β-diketone derivatives; (Z)-3-(4-(4-aminophenoxy)phenylamino)-1,3-diphenylprop-2-en-1-one(L1) and (2Z,2Z)-3,3-(4,4-oxybis(4,1-phenylene)bis(azanediyl)bis(1,3-diphenylprop-2-en-1-one(L2) were synthesized and characterized by spectral and single crystal analysis XRD illustrate the compounds are in the form of Ketamine The study evaluated the cytotoxicity and apoptotic effect of L1 and L2 and similar ketamines against human breast cancer cell lines (MCF 7). O-linkage exhibits greater anticancer activity with inhibitory concentration (IC) values50) comparable to the standard drug (tamoxifen). Further investigations using DCFH-DA and DAPI staining assay revealed that the compounds induce cellular apoptosis through intracellular production of Reactive Oxygen Species (ROS). To investigate further, the binding attribute of L1-L4 with CT DNA was evaluated, and the compounds were coupled with sequence DNA duplex, d(CGCGAATTCGCG)2and breast cancer protease (3EU7).

    (Video) B.Sc. III Year | Organic synthesis via enolates | Keto enol tautomerism of ethyl acetoacetate
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(Video) mod05lec34 - Enols and Enolates_Intro

Copyright © 1986 Published by Elsevier B.V.


Which technique is used to study keto-enol tautomerism? ›

Compound 3 shows intra-molecular hydrogen bonding together with keto-enol tautomerism, which was determined using FTIR, 1H-NMR, 13C-NMR, and UV-Visible spectroscopy.

What is an example of a keto-enol tautomerism? ›

Examples of Keto-Enol tautomerism

These include acetone, ethyl acetate, and ethyl acetoacetate [1-9].

What is the relationship between keto and enol tautomers? ›

Aldehydes and ketones that have a proton on the alpha carbon can participate in keto-enol tautomerism, where an equilibrium exists between two constitutional isomers – the keto and enol forms. Constitutional isomers that are in equilibrium are called “tautomers”.

What are the factors affecting keto-enol tautomerism? ›

There are many factors that affect the keto or enol form, for example, polar solvent, high temperature, neutral pH and electron withdrawing substituents favor the keto form through intramolecular hydrogen bonding, whereas, nonpolar solvent, low temperature, high pH and electron donating groups favor the enol form ...

What is the function of keto-enol tautomerism? ›

Keto–enol tautomerism is important in several areas of biochemistry. The high phosphate-transfer potential of phosphoenolpyruvate results from the fact that the phosphorylated compound is "trapped" in the less thermodynamically favorable enol form, whereas after dephosphorylation it can assume the keto form.

How do you determine tautomerism? ›

Characteristics of Tautomerism-
  1. There is a movement of atoms involved which are alpha hydrogen atoms.
  2. The compounds can be separated and isolated as they are definite compounds.
  3. Tautomeric forms have two different structures.
  4. The compounds of tautomers are in equilibrium with each other.

What is a simple example for tautomerism? ›

In tautomerism, due to the delocalization of proton, if an open structure is changed to a ring structure, then such tautomer is called as ring-chain tautomers. Glucose is an example of ring-chain tautomers.

Which structures represent keto enol tautomers? ›

(d) Pent-1-ne-2-ol and 2-pentanone are keto enol tautomers. They can be isomerized into each other.

Which is more stable keto-enol tautomerism? ›

Enolic form of phenol is more stable than keto form by -13 kcal/mole of energy hence phenol exist exclusively as an enol. Enolic tautomer is less polar due to intramolecular hydrogen bonds than the corresponding keto form.

What is one of the major conditions for tautomerism? ›

The basic condition of tautomerism is the presence of acidic alpha hydrogen. The alpha hydrogen is hydrogen that is attached to alpha carbon (the carbon which is directly attached to a functional group).

Under what conditions would the keto form be more favored in the enol keto tautomerism experiment? ›

1 This intramolecular chemical equilibrium between keto and enol isomers is referred to as tautomerism. The chemical equilibrium is thermodynamically driven. Typically, the more stable keto form is favored at room temperature and above.

What factors affect the rate of tautomerization? ›

Tautomerism is an important phenomenon and an example of this process is the equilibrium in Schiff bases. These bases can exist as an equilibrium between two species, keto ⇌ enol [Scheme 1]. This process is affected by a number of factors such as solvent polarity, temperature and pH.

What is the significance of tautomerism? ›

Tautomers are structural isomers that differ from one another based on the position of proton(s) and double bonds (Antonov 2014). The presence of multiple tautomers is expected to increase the structural and chemical diversity of nucleic acid bases, as shown in Figure 1.

Which of the following will have least tendency to show tautomerism? ›

Final Step: Correct option (D) CH3OH.

How do you know which tautomer is more stable? ›

In the third tautomer we have conjugated double bonds which give extra stability so III is the most stable. Among the first and second tautomers, the first tautomer is the enol form and the second is the keto form. We know that keto is more stable than enol tautomer so structure II is more stable than structure I.

What is the most common tautomerism? ›

Prototropy is the most common form of tautomerism and refers to the relocation of a hydrogen atom. Prototropic tautomerism may be considered a subset of acid-base behavior.

Which structure can show tautomerism? ›

Keto compounds show tautomerism.

Is keto or enol favored at equilibrium? ›

In the absence of special stabilizing factors, equilibrium usually favors the “keto” form (so called, even though it could be an aldehyde) over the enol form. The tautomerizaton process can also be base-catalyzed.

Why is enol less stable than ketone? ›

In general, enols are less stable than their keto equivalents because of the favorability of the C=O. double bond over C=C double bond. However, enols can be stabilized kinetically or thermodynamically.

Which enol forms are most stable? ›

The stabilizing effect of enolic form is the intramolecular hydrogen bond present in enols. This provides another source of increasing bonding and hence, increased stabilization. Thus, CH3COCH2COOC2H5 is more stable.

Which of the following tautomers is more stable and why? ›

which of the tautomers is more stable and why? Trans isomer is more stable than cis isomer.

Which of the following compounds can exhibit tautomerism only one correct answer? ›

So, nitromethane shows tautomerism.

How many of the following will not show tautomerism? ›

Two, i.e., benzoquinone and benzaldehyde.

Which conditions is likely to increase ketone production? ›

When carbohydrate stores are significantly decreased or fatty acid concentration increases, there is an upregulation of the ketogenic pathway and an increased production of ketone bodies. This can be seen in conditions such as type 1 diabetes, alcoholism, and starvation.

What are the factors affecting enol content? ›

It depends on structural factor, temperature and nature of solvent. Resonance and hydrogen bonding increases enol content. Enolic form of phenol is more stable than keto form by -13 kcal/mole of energy hence phenol exist exclusively as an enol.

What causes tautomeric shift of bases? ›

The spontaneous isomerization of a nitrogen base to an alternative hydrogen-bonding form, possibly resulting in a mutation. Reversible shifts of proton position in a molecule. bases in nucleic acids shift between keto and enol forms or between amino and imino forms.

Which is the most contributing tautomeric enol? ›


Can keto-enol tautomerism be studied by IR spectroscopy? ›

Study of keto-enol tautomerism

The β-diketones and β- ketoesters exist as a tautomeric mixtures and hence their IR spectra will show the absorptions due to both keto and enol forms. And also the absorption due to the C=O group will be lowered due to the intramolecular hydrogen bonding in such compounds.

Is keto enol tautomerization a fast process or a slow process? ›

Mechanism for Catalyzed Keto-Enol Tautomerization

In neutral medial, tautomerization is slow but it can be speed up by catalysis with acids or bases.

How do you identify ketones on IR spectrum? ›

Aldehydes and ketones show a strong, prominent, stake-shaped band around 1710 - 1720 cm-1 (right in the middle of the spectrum). This band is due to the highly polar C=O bond. Because of its position, shape, and size, it is hard to miss.

Which of the following does not show keto-enol tautomerism? ›

Solution: In order to show keto-enol tautomerism, the compound must contain at least one α-hydrogen atom attached to sp3 hybridized carbon atom, which is not in case of compound present in option-D.

Which of the choices shows a keto-enol tautomeric pair? ›

(d) Pent-1-ne-2-ol and 2-pentanone are keto enol tautomers.

Does temperature affect keto-enol tautomerism? ›

Temperature was also found to significantly influence the keto–enol–enolate equilibrium, as well as the aggregation of curcumin. Keto–enol tautomerization was observed to be enthalpy driven at both acidic and neutral pH.

What is the mechanism of tautomerization reaction? ›

Tautomerization does not occur by the intramolecular transfer of a proton between carbon and oxygen atoms. Rather, a series of proton transfer steps between each tautomer, and the solvent occurs. The solvent acts as a mediator, accepting a proton from one form and giving it to the other form.

Which structure is most stable tautomerism? ›

In the third tautomer we have conjugated double bonds which give extra stability so III is the most stable. Among the first and second tautomers, the first tautomer is the enol form and the second is the keto form. We know that keto is more stable than enol tautomer so structure II is more stable than structure I.

Why does tautomerism occurs? ›

The difference between resonance and tautomerism is that resonance occurs due to the interaction between lone electron pairs Page 3 and bond electron pairs whereas tautomerism occurs due to the interconversion of organic compounds by relocating a proton.

Why is the enol form more stable? ›

The stabilizing effect of enolic form is the intramolecular hydrogen bond present in enols. This provides another source of increasing bonding and hence, increased stabilization. Thus, CH3COCH2COOC2H5 is more stable.


1. Enols and Enolates - Reactivity, Halogenation, and Alkylation: Crash Course Organic Chemistry #43
2. Chem 51C. Organic Chemistry. Lec. 14: Reactions at the Alpha-Carbon
(UCI Open)
3. Metal beta Diketonates, beta Diketone as Ligand, Acetylacetone (acac), Tautomerism in beta Diketone
(Dr. Geeta Tewari)
4. Calculating Percent Composition from 1H NMR
(CSB SJU Chemistry)
5. Med-pathway MCAT Test Prep Organic Chemistry Review.
(Phil Carpenter)
6. Strategies to Prepare Complex Molecules: Target-Driven Synthesis and Reactivity-Driven Methodology
(Andrews University)


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