Keto–Enol Tautomerism of Phenindione and Its Derivatives: An NMR and Density Functional Theory (DFT) Reinvestigation

Sigalov, M. V.

doi:10.1021/jp512461c

Cited by 9 publications

(9 citation statements)

References 34 publications

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“…Tautomerisms are structural isomers that differ from one another on the basis of the position of proton(s) and double bonds; the carbon skeleton of the structure is unchanged [1]. It was first described by Laarin in 1886 [2].Keto-enol tautomerism in β-ketoester [3][4][5], β-diketones [6][7][8][9], β-ketonitrile [10], β-ketoamide [11][12][13], ortho-hydroxy Schiff bases [14][15][16][17], Azo dyes [18], alpha-ketophosphonates [19], and the 1,3,4-thiadiazole group with a 2,4-hydroxyphenyl function [20] have been studied using different spectroscopic techniques. Similarly, those compounds of type β-keto-enol derivatives containing heterocyclic moieties such as 4-hydroxycoumarin [21], Imidazoline derivatives [22], indol [23], and pyrazole, pyridine, thiophene, or furan [24] can exist as a keto-enol tautomerism.…”

Section: Introductionmentioning

confidence: 99%

Synthesis, Spectroscopic Studies and Keto-Enol Tautomerism of Novel 1,3,4-Thiadiazole Derivative Containing 3-Mercaptobutan-2-one and Quinazolin-4-one Moieties

et al. 2020

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In this study, a novel 1,3,4-thiadiazole derivative containing 3-mercaptobutan-2-one and quinazolin-4-one moieties (Compound 3) is synthesized by the coupling of 2-amino-1,3,4-thiadiazole-5-(3-mercaptobutan-2-one) (Compound 1) with 2-Phenyl-4H-3,1-benzoxazin-4-one (Compound 2) in one molecule moiety. Compound 3 is found to exist as two types of intra-molecular hydrogen bonding with keto-enol tautomerism characters, which is further confirmed using FTIR, 1H-NMR, 13C-NMR, mass spectrometer, and UV-Visible spectra. The 1H-NMR and UV-Visible spectra of Compound 3 are investigated in different solvents such as methanol, chloroform, and DMSO. Compound 3 exhibits keto-enol tautomeric forms in solvents with different percentage ratios depending on the solvent polarity. The 1H-NMR and UV-Visible spectral results show that Compound 3 favors the keto over the enol form in polar aprotic solvents such as DMSO and the enol over the keto form in non-polar solvents such as chloroform. The 13C-NMR spectrum gives two singles at δ 204.5 ppm, due to ketonic carbon, and δ 155.5 ppm, due to enolic carbon, confirming the keto-enol tautomerism of Compound 3. Furthermore, the molecular ion at m/z 43 and m/z 407 in the mass spectrum of Compound 3 and fragmentation mechanisms proposed reveal the existence of the keto and enol forms, respectively.

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Section: Introductionmentioning

confidence: 99%

Synthesis, Spectroscopic Studies and Keto-Enol Tautomerism of Novel 1,3,4-Thiadiazole Derivative Containing 3-Mercaptobutan-2-one and Quinazolin-4-one Moieties

et al. 2020

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“…β-Diketones commonly exhibit keto–enol tautomerism. The diketo forms of both phthalimide and 1,3-indandione are the prevalent species in the gas phase; however, 1,3-indandione has been known to exhibit significant tautomerization to the keto–enol form in dimethyl sulfoxide, a highly polar solvent . There is evidence that the gas-phase form of a molecule may not be the species that adsorbs on a metal surface.…”

Section: Resultsmentioning

confidence: 99%

“…The diketo forms of both phthalimide 54 and 1,3-indandione 55 are the prevalent species in the gas phase; however, 1,3-indandione has been known to exhibit significant tautomerization to the keto−enol form in dimethyl sulfoxide, a highly polar solvent. 55 There is evidence that the gas-phase form of a molecule may not be the species that adsorbs on a metal surface. Although it has been well-established that deprotonation of carboxyl groups can occur upon adsorption on the more reactive Cu(111) substrate, 56−58 anthraquinone-2-carboxylic acid is known to chemisorb on gold in the carboxylate form.…”

Section: ■ Methodsmentioning

confidence: 99%

Scanning Tunneling Microscopy Investigation of Two-Dimensional Polymorphism of Structural Isomers

et al. 2018

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Monolayers of two pairs of structural isomers were deposited on Au(111) and observed via scanning tunneling microscopy in ultrahigh vacuum. We observe exclusively cyclic pentamers of isatin (1H-indole-2,3-dione), whereas its structural isomer, phthalimide (isoindole-1,3-dione), self-assembles primarily into close-packed arrays, with alternate structures that include kinetically locked disordered clusters and tetramer networks. Removal of the phthalimide NH group and its replacement with a CH2 group produces 1,3-indandione, which, despite the loss of the hydrogen-bond donor site, self-assembles into similar structures: close-packed areas and tetramer networks. The equivalent analog for isatin, 1,2-indandione, does not form pentamers and instead forms only close-packed areas and disordered regions. By iteratively altering the chemical structure, we demonstrate the influence that the chemical structure has on the resulting two-dimensional self-assembly.

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“…The newly formed enol O-H bond participates in the intermolecular hydrogen bond rather than in the intramolecular one. NMR spectroscopy and DFT calculations of phenindione (cyclic 1,3-diketone) and derivatives showed that the predominant tautomer for these compounds in DMSO solution is enol form [26].…”

Section: Scheme 1 Tautomerization Of 4-phenyl-24-dioxobutanoic Acid mentioning

confidence: 99%

Tautomerism of 4-phenyl-2,4-dioxobutanoic acid. Insights from pH ramping NMR study and quantum chemical calculations

Cvijetić¹,

Pešić

Todorov

et al. 2017

Struct Chem

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Aryldiketo acids (ADKs) exhibit the variety of biological activities, mainly due to large affinity toward divalent metal ions. Metal complexation ability of ADKs, as well as interactions with proteins, depend on tautomeric form present in solution. The main aim of this study was to fully explore the tautomeric preferences of 4-phenyl-2,4-dioxobutanoic acid (4PDA), as ADKs representative, in aqueous media at different pH values. 1D and 2D NMR spectroscopy in combination with quantum chemical calculations was applied in order to better understand the tautomeric preferences of 4PDA. The data in highly acidic media are especially interesting since there are no such findings in the literature due to low solubility of ADKs in molecular form. At low pH values, where 4PDA is unionized, the most abundant tautomeric form is enol with keto group closer to phenyl ring. At higher pH values, mixture of two 4PDA ionic forms coexists in solution. Their ratio calculated according to NMR data fits the values predicted using two experimentally determined pKa values. Based on the complexity of 1 H NMR spectrum of monoanionic 4PDA form, coexistence of two stable rotamers was assumed. In an alkaline media 4PDA is mostly present in dianionic form. As π-electrons of dianion are delocalized over an entire keto-enol moiety, spectral distinction between tautomers was not possible. Quantum chemical calculations were used to predict relative stability of tautomers. The predictions were in good accordance with experimental results only in case when explicit water molecule was included in calculations.

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Keto–Enol Tautomerism of Phenindione and Its Derivatives: An NMR and Density Functional Theory (DFT) Reinvestigation

Cited by 9 publications

References 34 publications

Synthesis, Spectroscopic Studies and Keto-Enol Tautomerism of Novel 1,3,4-Thiadiazole Derivative Containing 3-Mercaptobutan-2-one and Quinazolin-4-one Moieties

Synthesis, Spectroscopic Studies and Keto-Enol Tautomerism of Novel 1,3,4-Thiadiazole Derivative Containing 3-Mercaptobutan-2-one and Quinazolin-4-one Moieties

Scanning Tunneling Microscopy Investigation of Two-Dimensional Polymorphism of Structural Isomers

Tautomerism of 4-phenyl-2,4-dioxobutanoic acid. Insights from pH ramping NMR study and quantum chemical calculations

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