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Journal articles on the topic 'Tautomerism'

Author: Grafiati

Published: 4 June 2021

Last updated: 25 July 2025

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1

Mirkovic, Jelena, Gordana Uscumlic, Aleksandar Marinkovic, and Dusan Mijin. "Azo-hydrazone tautomerism of aryl azo pyridone dyes." Chemical Industry 67, no. 1 (2013): 1–15. http://dx.doi.org/10.2298/hemind120309053m.

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In the last three or four decades disperse dyes derived from pyridones (in particular azo pyridone dyes) have gained in importance, and are widely used in various fields. These compounds have excellent coloration properties, and are suitable for the dyeing of polyester fabrics. Basic features of these dyes are simplicity of their synthesis by diazotation and azo coupling. They generally have high molar extinction coefficient with medium to high light and wet fastness. The absorption maxima of these dyes show their visible absorption wavelength ranging from yellow to orange, which can be attrib

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2

Hansen, Poul Erik. "Tautomerism of β-Diketones and β-Thioxoketones". Encyclopedia 3, № 1 (2023): 182–201. http://dx.doi.org/10.3390/encyclopedia3010013.

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The present overview concentrates on recent developments of tautomerism of β-diketones and β-thioxoketones, both in solution and in the solid state. In particular, the latter has been a matter of debate and unresolved problems. Measurements of 13C, 17O, and 2H chemical shifts have been used. Deuterium isotope effects on chemical shifts are proposed as a tool in the study of this problem. Photoconversion of β-diketones and β-thioxoketones are discussed in detail, and the incorporation of β-diketones into molecules with fluorescent properties is assessed. Finally, docking studies of β-diketones

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3

Raczyńska, Ewa Daniela, Jean-François Gal, and Pierre-Charles Maria. "Potential Push-Pull Carbon Superbases Based on Methyl Substitution of Rare Tautomers of Imines." Molecules 30, no. 3 (2025): 474. https://doi.org/10.3390/molecules30030474.

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Push-pull imines with strong electron donor group(s) display exceptional basicity in the gas phase. Most of them do not exhibit prototropic tautomerism, and gas-phase acid-base equilibria have been already well described and reviewed. Some questions remain for tautomeric systems, particularly for their uncommon forms. As shown by quantum-chemical calculations, some often-neglected tautomers display higher basicity than the thermodynamically favored forms. However, their participation in tautomeric mixtures being in equilibrium is negligible, and their basicity can be impossible to measure in t

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4

Oziminski, Wojciech P., and Agata Wójtowicz. "New theoretical insights on tautomerism of hyperforin—a prenylated phloroglucinol derivative which may be responsible for St. John’s wort ( Hypericum perforatum ) antidepressant activity." Structural Chemistry 31, no. 2 (2019): 657–66. http://dx.doi.org/10.1007/s11224-019-01434-6.

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AbstractThe thermodynamic aspects of keto-enol tautomerism of hyperforin were investigated theoretically using density functional theory methods. At the B3LYP/aug-cc-pVTZ//B3LYP/aug-cc-pVDZ level of theory the enol tautomer dominates the tautomeric mixture and the second enol tautomer 1OH-HB has Gibbs free energy higher by 1.2 kcal/mol, despite possessing an intramolecular hydrogen bond. The purely keto tautomer is less stable by 3.3 kcal/mol compared with the 1OH tautomer, which means that the percentage of the keto tautomer in the tautomeric mixture is only about 0.4%. This is a different pi

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5

Fabian, Walter M. F. "Tautomerism in Five-membered Nitrogen Heterocycles. A Test of the Reliability of Semiempirical (AMI, PM3, MNDO) Quantum Chemical Methods." Zeitschrift für Naturforschung A 45, no. 11-12 (1990): 1328–34. http://dx.doi.org/10.1515/zna-1990-11-1216.

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AbstractThe reliability of three popular semiempirical quantum chemical methods (AM1, PM3, MNDO) for the treatment of tautomeric equilibria is tested in a series of five-membered nitrogen heterocycles. The known flaw of MNDO to overestimate the stability of compounds with two or more adjacent pyridine-like lone pairs is also present in AM1 and to a somewhat lesser extent in PM3. Tautomeric species differing in the number of adjacent pyridine-like lone pairs, thus, cannot be adequately treated by these semiempirical methods. Both AM1 as well as PM3, however, represent major improvements over MN

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6

Raczyńska, Ewa Daniela, Pierre-Charles Maria, and Jean-François Gal. "Quantum Chemical Studies on the Prototropic and Acid/Base Equilibria for 2-Aminopyrrole in Vacuo—Role of CH Tautomers in the Design of Strong Brønsted Imino N-Bases." Molecules 30, no. 10 (2025): 2112. https://doi.org/10.3390/molecules30102112.

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In the quest of the pivotal origin of the very strong gas-phase proton basicity for some iminopyrrole derivatives, proposed in the literature on the basis of quantum chemical calculations, the full tautomeric and acid/base equilibria were investigated in vacuo for 2-aminopyrrole exhibiting enamino–imino tautomerism. Thermochemistry of these processes investigated at the Density Functional Theory (DFT) level indicates a lower stability for the imino than for the enamino tautomers. However, the imino N atom in the imino forms displays an exceptionally high basicity, particularly in the minor and

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7

Allegretti, P. E., C. B. Milazzo, and J. J. P. Furlong. "Mass Spectrometry as a Tool for the Determination of Heats of Tautomerization of Thioamides in the Gas Phase." European Journal of Mass Spectrometry 11, no. 1 (2005): 53–63. http://dx.doi.org/10.1255/ejms.691.

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Tautomerism of several thioamides was studied by mass spectrometry. The analysis of the corresponding mass spectra allowed some fragmentations to be assigned to specific tautomers and heats of tautomerization to be determined through temperature effects and electron energy studies. Experimental determinations were strongly supported by theoretical calculations. AM1 semi-empirical results indicate that the thioamide–thioimidol equilibrium can be studied by mass spectrometry. Also, additional evidence was obtained regarding tautomerism occurrence between neutral species.

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8

Stoyanov, Stefan, Ivan Petkov, Liudmil Antonov, Tatyana Stoyanova, Petros Karagiannidis, and Paraskevas Aslanidis. "Thione–thiol tautomerism and stability of 2- and 4-mercaptopyridines and 2-mercaptopyrimidines." Canadian Journal of Chemistry 68, no. 9 (1990): 1482–89. http://dx.doi.org/10.1139/v90-227.

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The possible thione–thiol tautomerism of 2- and 4-mercaptopyridines, 2-mercaptopyrimidine, and 4,6-dimethyl-2-mercaptopyrimidine in solution is studied by means of absorption (UV–VIS) spectroscopy. In accordance with earlier observations, polar solvents and self-association shift the apparent tautomeric equilibrium significantly towards the thione form. In dilute solutions of nonpolar solvents the thiol form predominates. On standing, significant changes are observed in the absorption spectra of these tautomeric compounds in ethanol, dioxane, and water. The time course of the tautomerization,

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9

Zaharieva, Lidia, Vera Deneva, Fadhil S. Kamounah, et al. "Tautomerism and switching in 7-hydroxy-8-(azophenyl)quinoline and similar compounds." Beilstein Journal of Organic Chemistry 21 (July 10, 2025): 1404–21. https://doi.org/10.3762/bjoc.21.105.

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Tautomerism in two new azo dyes, based on 7-hydroxyquinoline, has been considered from the viewpoint of the proton crane concept. Although 8-(phenyldiazenyl)quinolin-7-ol exists in solution as a mixture of azo and two hydrazone tautomers, as shown by the experimental and theoretical results, upon irradiation switching, based on long-range proton transfer, occurs in a limited extent. 8-(4-Hydroxy-1,2,3,5-tetrafluorophenyldiazenyl)quinolin-7-ol exists as a single enol (azo) tautomer and the reduced basicity of the azo group nitrogen atoms does not allow shift of the tautomeric state neither upon

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10

Sun, Chun-Lin, Xiao-E. Luo, Huan Xu та ін. "Aromaticity and tautomerism of a 4n π electron dihydrohexaazapentacene". Organic Chemistry Frontiers 7, № 2 (2020): 405–13. http://dx.doi.org/10.1039/c9qo01285k.

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We report herein the intriguing tautomerism behaviors of new dihydrohexaazapentacene derivatives. The dihydrohexaazapentacene molecules with 4n π electrons exist as two stable tautomers in solution and exhibits globe aromaticity.

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11

Avendaño, Carmen, María Teresa Ramos, José Elguero, María Luisa Jimeno, Juana Bellanato, and Feliciana Florencio. "Tautomerism of bis(2-benzothiazolyl)methanes." Canadian Journal of Chemistry 66, no. 6 (1988): 1467–73. http://dx.doi.org/10.1139/v88-236.

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Tautomerism of dibenzothiazolylmethane (1) and its C-methyl derivative (2) has been studied by 1H nuclear magnetic resonance, ultraviolet, and infrared spectroscopy using C,C-dimethyl (3) and N-methyl (4) derivatives as model compounds of the "CH" and "NH" forms, respectively. X-ray diffraction analysis of the "fixed" N-methyl derivative 4 shows that it corresponds to the Z-sE isomer 4b2. The CH tautomers are unstable in solution and they slowly isomerize into a mixture of NH tautomers that depends on the solvent and on the C-substituent (H or CH3).

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12

Štoček, Jakub Radek, and Martin Dračínský. "Tautomerism of Guanine Analogues." Biomolecules 10, no. 2 (2020): 170. http://dx.doi.org/10.3390/biom10020170.

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Tautomerism of nucleic acid (NA) bases is a crucial factor for the maintenance and translation of genetic information in organisms. Only canonical tautomers of NA bases can form hydrogen-bonded complexes with their natural counterparts. On the other hand, rare tautomers of nucleobases have been proposed to be involved in processes catalysed by NA enzymes. Isocytosine, which can be considered as a structural fragment of guanine, is known to have two stable tautomers both in solution and solid states. The tautomer equilibrium of isocytosine contrasts with the remarkable stability of the canonica

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13

Abdeldjebar, Hasnia, Yamina Belmiloud, Wassila Djitli, Sofien Achour, Meziane Brahimi, and Bahoueddine Tangour. "Proton transfer in the benzimidazolone and benzimidazolthione tautomerism process catalyzed by polar protic solvents." Progress in Reaction Kinetics and Mechanism 44, no. 2 (2019): 143–56. http://dx.doi.org/10.1177/1468678319825740.

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The tautomeric equilibrium of benzimidazolone and benzimidazolthione have been studied by the density functional theory method using the CAM-B3LYP functional together with the 6-311G(d,p) basis set. Two separate mechanisms have been investigated: a direct intramolecular transfer using the polarizable continuum model and an indirect proton transfer assisted by a molecule of solvent (C6H12, H2O, CH3OH, and H2O2). In both cases, the results obtained indicate that ketone and thione are the most stable forms. However, the enhanced height of the activation barrier for the four-center mechanisms desc

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14

Pis-Diez, Reinaldo, Gustavo A. Echeverría, Oscar E. Piro, Jorge L. Jios, and Beatriz S. Parajón-Costa. "A structural, spectroscopic and theoretical study of an o-vanillin Schiff base derivative involved in enol-imine and keto-amine tautomerism." New Journal of Chemistry 40, no. 3 (2016): 2730–40. http://dx.doi.org/10.1039/c5nj01039j.

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The potassium salt of the Schiff base derived from o-vanillin and taurine is involved in enol-imine (I) and keto-amine (II) tautomerism. Both tautomeric forms coexist in the crystal and they are stabilized by strong O–H⋯N and O⋯H–N intramolecular hydrogen bonds.

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15

Slota, Michael, Marian Blankenhorn, Eric Heintze, Minh Vu, Ralph Hübner, and Lapo Bogani. "Photoswitchable stable charge-distributed states in a new cobalt complex exhibiting photo-induced valence tautomerism." Faraday Discussions 185 (2015): 347–59. http://dx.doi.org/10.1039/c5fd00088b.

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We report the synthesis and magnetic and photomagnetic behaviour of a novel valence tautomeric cobalt complex, [Co(3,5-dbbq)<sub>2</sub>(μ-bpym)] (1) (3,5-dbbq = 3,5-di-tert-butyl-1,2-benzoquinone and μ-bpym = 2,2′-bipyrimidine). The synthesis is performed by reacting Co<sub>2</sub>(CO)<sub>8</sub> and μ-bpym in the presence of the ligand 3,5-dbbq in a mixed solvent under inert atmosphere. The magnetic behavior clearly shows the presence of electron transfer from the catecholate ligand to the cobalt center, producing valence tautomers of [Co<sup>II</sup>(SQ)<sub>2</sub>] with a transition temp

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16

Colasurdo, Diego D., Matías N. Pila, Dacio A. Iglesias, Sergio L. Laurella, and Danila L. Ruiz. "Tautomerism of uracil and related compounds: A mass spectrometry study." European Journal of Mass Spectrometry 24, no. 2 (2017): 214–24. http://dx.doi.org/10.1177/1469066717712461.

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It has been demonstrated that uracil has a preponderant tautomeric form, but it is also known that different tautomers co-exist in this equilibrium. In this work, mass spectrometry is used as a helpful tool to analyse the equilibria, using derivative compounds to forbid the presence of some tautomers and ion trap mass spectrometry to follow relevant fragmentation pathways. Theoretical calculations were performed to confirm tautomers abundance by energy minimization in gas phase. Analysis of mass spectra of uracil, three methyl-substituted uracils, 2-thiouracil and three benzouracils suggest th

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17

Chermahini, Alireza Najafi, Hossein A. Dabbagh, and Abbas Teimouri. "Theoretical studies on tautomerism of dihydropyrimidine tautomers." Journal of Molecular Structure: THEOCHEM 857, no. 1-3 (2008): 105–10. http://dx.doi.org/10.1016/j.theochem.2008.02.012.

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18

Kwiatkowski, Adam, Erkki Kolehmainen, and Borys Ośmiałowski. "Conformational and Tautomeric Control by Supramolecular Approach in Ureido-N-iso-propyl,N’-4-(3-pyridin-2-one)pyrimidine." Molecules 24, no. 13 (2019): 2491. http://dx.doi.org/10.3390/molecules24132491.

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Ureido-N-iso-propyl,N’-4-(3-pyridin-2-one)pyrimidine (1) and its 2-methoxy pyridine derivative (1Me) has been designed and prepared. The conformational equilibrium in urea moiety and tautomerism in the pyrimidine part have been investigated by variable temperature and 1H NMR titrations as well as DFT quantum chemical calculations. The studied compounds readily associate by triple hydrogen bonding with 2-aminonaphthyridine (A) and/or 2,6-bis(acetylamino)pyridine (B). In 1, the proton is forced to 1,3-tautomeric shift upon stimuli and keeps it position, even when one of the partners in the compl

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19

Dykun, Oleksii, Viktor Anishchenko, Andrii Redko, and Volodymyr Rybachenko. "Comparison of radical scavenging properties of gosypol and its derivatives in the reaction with DPPH." Kharkov University Bulletin Chemical Series, no. 42 (June 21, 2024): 62–67. https://doi.org/10.26565/2220-637x-2024-42-07.

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Radical scavenging activity of 7,7'-ditosyloxygossypol in reaction with 2,2'-diphenyl-1-piсrylhydrazyl (DPPH) in ethanol was evaluated by total stoichiometries and EC50 values. The stoichiometric coefficient of the reaction of DPPH with 7,7'-ditosyloxygossypol is close to two. This indicates that in ethanol this compound exists mainly in the dilactol tautomeric form, and the lactol hydroxyl groups are not capable of reacting with DPPH. Such a result can be an indirect confirmation that no tautomeric transformation occurs during the reaction with DPPH due to the consumption of one of the tautom

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20

Milata, Viktor. "Nitro and aminobenzimidazoles." Acta Chimica Slovaca 11, no. 2 (2018): 182–88. http://dx.doi.org/10.2478/acs-2018-0026.

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AbstractA summary of the preparation methods of 2 tautomeric and 4N-methylated benzimidazoles with a nitro group on the benzene ring (1–6) and with an amino group in the same positions (7–12) were summarized. Annular tautomerism of the title compounds1–12has been studied using1H,13C and15N NMR spectra in liquid and solid state (CPMAS), UV spectra and quantum chemical calculations.

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21

López, Concepción, Rosa María Claramunt, Ibon Alkorta, and José Elguero. "Solution and solid state (CPMAS) NMR studies of the tautomerism of six-membered heterocyclic compounds related to 2-pyridones." Spectroscopy 14, no. 3 (2000): 121–26. http://dx.doi.org/10.1155/2000/421654.

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Several13C and15N chemical shifts of 2-pyridone(1), 4(3H)-pyrimidone(2), uracil(3)and cytosine(4)have been measured in solution and in the solid state. These data have been discussed in relation with the tautomerism of the four heterocycles. GIAOab initiocalculations of absolute shieldings have been carried out to identify the predominant tautomers in the case of compounds(1)and(2).

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22

Mchedlov-Petrossyan, Nikolay O., and Natalya A. Vodolazkaya. "Protolytic Equilibria in Organized Solutions: Ionization and Tautomerism of Fluorescein Dyes and Related Indicators in Cetyltrimethylammonium Chloride Micellar Solutions at High Ionic Strength of the Bulk Phase." Liquids 1, no. 1 (2021): 1–24. http://dx.doi.org/10.3390/liquids1010001.

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Ionic equilibrium of 22 hydroxyxanthenes, including halogen and nitro derivatives of fluorescein, and their thio- and aza analogues, were studied spectrophotometrically in micellar solutions of cetyltrimethylammonium chloride at ionic strength of the bulk phase 4.0 M KCl. This micellar pseudophase is characterized by the electrostatic surface potential of +(15–16) mV and the ETN value of 0.623. In the case of dyes bearing the COOH group, colorless lactone is the predominant tautomer of the molecular form H2R. A new classification of fluoresceins is developed. The dyes were divided into four gr

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23

Saraví Cisneros, Hebe, Sergio Laurella, Danila L. Ruiz, Agustín Ponzinibbio, Patricia E. Allegretti, and Jorge J. P. Furlong. "Spectrometric Study of the Nitrile-Ketenimine Tautomerism." International Journal of Spectroscopy 2009 (September 9, 2009): 1–18. http://dx.doi.org/10.1155/2009/408345.

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Mass spectrometry is used to evaluate the occurrence of the nitrile-ketenimine tautomerism. Mass spectra of two differently substituted nitriles, ethyl-4,4-dicyano-3-methyl-3-butenoate and diethyl-2-cyano-3-methyl-2-pentenodiate are examined looking for common mass spectral behaviors. Ion fragmentation assignments for specific tautomers allow to predict the presence of the corresponding structures. Additionally, the mass spectrum and nuclear magnetic resonance spectra of ethyl-4,4-dicyano-2,2-diethyl-3-methyl-3-butenoate and that of the corresponding amination product support the occurrence of

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24

Traven, Valery F., Vadim V. Negrebetsky, Larisa I. Vorobjeva, and Edward Andrew Carberry. "Keto–enol tautomerism, NMR spectra, and H–D exchange of 4-hydroxycoumarins." Canadian Journal of Chemistry 75, no. 4 (1997): 377–83. http://dx.doi.org/10.1139/v97-043.

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4-Hydroxycoumarin 1, 4,5-dihydroxycoumarin 2, and 4,7-dihydroxycoumarin 3 undergo H–D exchange at the C(3) atom of the lactone ring. Although only the 4-hydroxy-2-chromenone tautomeric forms are seen in the 1H and 13C NMR spectra of compounds 1–3, the equilibrium between the 4-hydroxy-2-chromenone and 2,4-chromandione forms is suggested to be the key step in the H–D exchange reaction. 4,5-Dihydroxycoumarin shows the highest rate of the reaction, since H-bonding between 5-hydroxyl and 4-keto functional groups can provide relative stability to the 5-hydroxy-2,4-chromandione tautomeric form, a pr

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25

Iglesias, Dacio Adhemar, Danila Luján Ruiz, and Patricia Ercilia Allegretti. "2-Cyanobenzoic Acids: Tautomeric Equilibria Study." Australian Journal of Chemistry 68, no. 3 (2015): 461. http://dx.doi.org/10.1071/ch14273.

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Evidence of ring–chain tautomerism in the gas phase from mass spectrometry and in solution determined by means of 1H NMR and 13C NMR is reported for 2-cyanobenzoic acids. The analysis of the corresponding spectra has allowed specific assignment of fragment ions to tautomers. The predictive value of this methodology is supported by the influence of the substitution pattern of these compounds on this equilibrium.

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26

Türker, Lemi. "Tautomerism in 11-Hydroxyaklavinone: A DFT Study." Scientific World Journal 2012 (2012): 1–7. http://dx.doi.org/10.1100/2012/526289.

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The antharquinone-based chromophore of 11-hydroxyaklavinone is present in the structure of an anticancer agent, daunomycin. On the other hand, aklavinone is the parent aglycone of certain anthracycline antibiotics that possess anti-cancer activity too. The structures of aklavinone and its 11-hydroxy derivative have many –OH groups, and two keto groups which may take place in certain tautomeric equilibria. Of these tautomeric forms, presently the one involving the anthraquinone based tautomers of 11-hydroxyaklavinone has been investigated quantum chemically in the framework of the density funct

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27

Borbulevych, Oleg, Roger I. Martin, Ian J. Tickle, and Lance M. Westerhoff. "XModeScore: a novel method for accurate protonation/tautomer-state determination using quantum-mechanically driven macromolecular X-ray crystallographic refinement." Acta Crystallographica Section D Structural Biology 72, no. 4 (2016): 586–98. http://dx.doi.org/10.1107/s2059798316002837.

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Gaining an understanding of the protein–ligand complex structure along with the proper protonation and explicit solvent effects can be important in obtaining meaningful results in structure-guided drug discovery and structure-based drug discovery. Unfortunately, protonation and tautomerism are difficult to establish with conventional methods because of difficulties in the experimental detection of H atoms owing to the well known limitations of X-ray crystallography. In the present work, it is demonstrated that semiempirical, quantum-mechanics-based macromolecular crystallographic refinement is

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28

Anisimova, N. A., and D. A. Melkova. "Acyl derivatives of 2,3,6,7-tetrahydro-1,4-diazepines: synthesis, structure, and tautomeric transformations." Журнал общей химии 93, no. 11 (2023): 1650–63. http://dx.doi.org/10.31857/s0044460x23110021.

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The reaction of 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene with carboxylic acid chlorides afforded a series of N -and C -acylsubstituted 2,3,6,7-tetrahydro-1,4-diazepines, which in solutions of deuterated solvents (CD3OD, DMCO) undergo keto-enol and imino-enamine tautomerism. Structure of the obtained N - and C -acyldiazepines and their tautomeric transformations were characterized by 1Н and 13С NMR spectroscopy using two-dimensional experiments 1Н-13С HMQC, HMBC, 1Н-1Н COSY.

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29

Antonov, Liudmil. "Tautomerism in Azo and Azomethyne Dyes: When and If Theory Meets Experiment." Molecules 24, no. 12 (2019): 2252. http://dx.doi.org/10.3390/molecules24122252.

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The performance of 26 hybrid density functionals was tested against a tautomeric dataset (TautData), containing experimental information for the keto-enol tautomeric equilibrium in 16 tautomeric azodyes and Schiff bases in cyclohexane, carbon tetrachloride and acetonitrile. The results have shown that MN12-SX, BHandH and M06-2X can be used to describe the tautomeric state of the core structures in the frame of ~0.5 kcal/mol error and correctly predict the tautomeric state in respect of dominating tautomeric form. Among them MN12-SX is the best performer, although it fails to describe the nonpl

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30

Deneva, Vera, Georgi Dobrikov, Aurelien Crochet, Daniela Nedeltcheva, Katharina M. Fromm, and Liudmil Antonov. "Tautomerism as primary signaling mechanism in metal sensing: the case of amide group." Beilstein Journal of Organic Chemistry 15 (August 8, 2019): 1898–906. http://dx.doi.org/10.3762/bjoc.15.185.

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The concept for sensing systems using the tautomerism as elementary signaling process has been further developed by synthesizing a ligand containing 4-(phenyldiazenyl)naphthalene-1-ol as a tautomeric block and an amide group as metal capturing antenna. Although it has been expected that the intramolecular hydrogen bonding (between the tautomeric hydroxy group and the nitrogen atom from the amide group) could stabilize the pure enol form in some solvents, the keto tautomer is also observed. This is a result from the formation of intramolecular associates in some solvents. Strong bathochromic an

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31

Obukhova, Olena M., Nikolay O. Mchedlov-Petrossyan, Natalya A. Vodolazkaya, Leonid D. Patsenker, and Andrey O. Doroshenko. "Stability of Rhodamine Lactone Cycle in Solutions: Chain–Ring Tautomerism, Acid–Base Equilibria, Interaction with Lewis Acids, and Fluorescence." Colorants 1, no. 1 (2022): 58–90. http://dx.doi.org/10.3390/colorants1010006.

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The equilibrium between different tautomers that can be colored or colorless is an important feature for rhodamine dyes. Presently, this phenomenon is mostly discussed for rhodamine B. Herein, we studied the tautomerism and acid–base dissociation (HR+ ⇄ R + H+) of a set of rhodamines in organic media. Form R is an equilibrium mixture of the colored zwitterion R± and colorless lactone R0. Absorption spectra in 90 mass% aqueous acetone reflects the correlation between the dyes structure and the equilibrium constant, KT = [R0]/[R±]. Increase in the pKa value on transferring from water to organic

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32

Kazeri-Shandiz, Shima, Ali Beyramabadi та Ali Morsali. "Geometry, tautomerism and non-covalent interactions of the drug halofuginone with the carbon-nanotube and γ-Fe2O3 nanoparticles: A DFT study". Journal of the Serbian Chemical Society 83, № 3 (2018): 305–15. http://dx.doi.org/10.2298/jsc170608100k.

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Halofuginone is a potential anti-malarial drug, which could exist as three possible tautomers. Herein, using density functional theory (DFT), and handling the solvent effects with the PCM model, the tautomerism of halofuginone was investigated. Intramolecular H-bonds play an important role in the stability of the tautomers. The conformer H1a is the most stable. Noncovalent interactions of the H1a conformer with the armchair (5,5) single-wall carbon nanotubes and ?-Fe2O3 nanoparticles were explored in several manners. The most stable form of them was determined. The intermolecular H-bonds play

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33

Tivendale, Nathan D., Noel W. Davies, James Horne, John J. Ross, and Jason A. Smith. "Analysis of the Enol–Keto Tautomers of Indole-3-pyruvic Acid." Australian Journal of Chemistry 68, no. 2 (2015): 345. http://dx.doi.org/10.1071/ch14343.

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Indole-3-pyruvic acid (IPyA) is an important naturally occurring biosynthetic intermediate whose quantitation by standard analytic techniques can be complicated as it can exist as either the keto or enol tautomer. Here, we present a detailed analysis of the tautomerism of IPyA and provide further evidence that the two tautomers of IPyA may be readily separated by ultra high-performance liquid chromatography and that the relative proportions of each form may be controlled using temperature and pH.

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34

Nieto, Carla I., Pilar Cabildo, M. Ángeles García, Rosa M. Claramunt, Ibon Alkorta, and José Elguero. "An experimental and theoretical NMR study of NH-benzimidazoles in solution and in the solid state: proton transfer and tautomerism." Beilstein Journal of Organic Chemistry 10 (July 16, 2014): 1620–29. http://dx.doi.org/10.3762/bjoc.10.168.

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This paper reports the 1H, 13C and 15N NMR experimental study of five benzimidazoles in solution and in the solid state (13C and 15N CPMAS NMR) as well as the theoretically calculated (GIAO/DFT) chemical shifts. We have assigned unambiguously the "tautomeric positions" (C3a/C7a, C4/C7 and C5/C6) of NH-benzimidazoles that, in some solvents and in the solid state, appear different (blocked tautomerism). In the case of 1H-benzimidazole itself we have measured the prototropic rate in HMPA-d 18.

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35

Hansen, Poul Erik. "Structural Studies of β-Diketones and Their Implications on Biological Effects". Pharmaceuticals 14, № 11 (2021): 1189. http://dx.doi.org/10.3390/ph14111189.

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The paper briefly summarizes methods to determine the structure of β-diketones with emphasis on NMR methods. Density functional calculations are also briefly treated. Emphasis is on the tautomeric equilibria of β-diketones in relation to biological effects. Relevant physical parameters such as acidity and solubility are treated. A series of biologically active molecules are treated with respect to structure (tautomerism). Characteristic molecules or groups of molecules are usnic acids, tetramic and tetronic acids, o-hydroxydibenzoylmethanes, curcumines, lupulones, and hyperforines.

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36

Lopez, Concepcion, Rosa Ma Claramunt, Swiatoslaw Trofimenko, and José Elguero. "A 13C NMR spectroscopy study of the structure of N-H pyrazoles and indazoles." Canadian Journal of Chemistry 71, no. 5 (1993): 678–84. http://dx.doi.org/10.1139/v93-092.

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The 13C chemical shifts and some 1H–13C coupling constants of 23 pyrazoles and indazoles are reported and discussed. The spectra were recorded in CDCl3 and in DMSO-d6 solutions and, in several cases, also in the solid state (CP/MAS technique). These data allow us to determine the tautomerism of these compounds in the solid state (usually only one tautomer) and in solution. The position of the tautomeric equilibrium is related to the Hammett σm value of the 3(5)-substituent.

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37

Garifzianova, Guzel G. "Theoretical study of the isomerization of 1-amino-4-phenylamino-9,10-anthraquinone." Butlerov Communications 60, no. 12 (2019): 37–42. http://dx.doi.org/10.37952/roi-jbc-01/19-60-12-37.

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This paper presents the results of computer simulation of tautomeric transformations of the molecule 1-amino-4-phenylamino-9,10-anthraquinone. It is known from the literature that the presence of substituents in the 1,4-position of anthraquinone-9,10 leads to various tautomeric transformations, with a shift in the absorption maximum and the appearance of absorption bands in the red wave region in electronic spectra. Both the 1-amino-4-hydroxyanthraquinone described in the literature and the 1-amino-4-phenylamino-9,10-anthraquinone are characterized by two types of prototropic tautomerism – ket

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38

Masuda, Seizo, Tahei Tomida, Masami Tanaka, and Yutaka Asahi. "Polymerizable tautomers, 11. Tautomerism and polymerization of p-vinylbenzoylacetone." Macromolecular Chemistry and Physics 196, no. 2 (1995): 621–28. http://dx.doi.org/10.1002/macp.1995.021960217.

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39

Anderson, John C., and A. Douglas Broadbent. "The influence of pH in the tautomerism of 9,10-anthracenediols and 1,3-diketones." Canadian Journal of Chemistry 64, no. 1 (1986): 127–32. http://dx.doi.org/10.1139/v86-022.

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Equations have been derived to describe how the ratio of the total concentration of all keto forms to that of all enolic forms (K′) varies with changing pH, for a tautomeric system in which the enol and ketone are polyprotic acids. The influence of pH on the tautomerism of 2-amino-9,10-anthracenediol, 2,9,10-anthracenetriol, 2,4-pentanedione, and 1-(3-pyridyl)-1,3-butanedione was examined. The equilibrium constants for all the acid–base equilibria involved were calculated from the dependence of K′ on pH.

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40

Solea, Atena B., Ivan Cornu, Vera Deneva, et al. "Tautomerism and Self-Association in the Solution of New Pinene-Bipyridine and Pinene-Phenanthroline Derivatives." Molecules 25, no. 2 (2020): 298. http://dx.doi.org/10.3390/molecules25020298.

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Two novel pinene-type ligands have been synthesized and their tautomeric and self-associating behavior studied in solution and in the solid state. The first ligand, an acetylated derivative of 5,6-pinene-bipyridine, displays keto-enol tautomerism in solution. This tautomeric equilibrium was studied by NMR and UV-Vis spectroscopy in various solvents, and the results were compared with the ones obtained through DFT calculations. The second ligand was obtained by an unusual oxidation of the phenanthroline unit of a pinene-phenanthroline derivative. This compound exists as a single tautomer in sol

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41

Albayrak Kaştaş, Çiğdem, and Gökhan Kaştaş. "Dependence of tautomerism on substituent type in o-hydroxy Schiff bases." Macedonian Journal of Chemistry and Chemical Engineering 38, no. 1 (2019): 85. http://dx.doi.org/10.20450/mjcce.2019.1531.

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Quantum computational methods were used to elucidate the structures of the o-hydroxy Schiff bases with different substituents. It is possible for a Schiff base to have different tautomeric structures depending on intramolecular proton transfer from the phenolic oxygen atom to the nitrogen atom. Proton transfer results in two tautomeric structures known as the phenol-imine and keto-amine forms. To explain the substituent effect on the proton transfer process in five o-hydroxy-Schiff bases, possible geometric structures in gas phase were optimized using density functional theory (DFT) at the B3L

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42

Nikitina, Polina A., Tatiana Yu Koldaeva, Marina A. Zakharko, and Valery P. Perevalov. "Synthesis and Study of Prototropic Tautomerism of 2-(2-Furyl)-1-hydroxyimidazoles." Australian Journal of Chemistry 73, no. 11 (2020): 1098. http://dx.doi.org/10.1071/ch20044.

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Novel 2-(2-furyl)imidazole derivatives were synthesised. 2-(2-Furyl)-1-methoxyimidazoles and 2-(2-furyl)-1-methylimidazole 3-oxides were used as model compounds in the study of the prototropic tautomerism of 2-(2-furyl)-1-hydroxyimidazoles by means of 1H, 13C NMR and UV/vis spectroscopies. It was demonstrated that the interaction of the π-excessive furyl moiety with an electron-withdrawing carbonyl group in position 5 of imidazole stabilised the N-hydroxy tautomeric form in both deuterated chloroform and d6-DMSO. In ethanol the N-oxide tautomer is also present along with the prevailing N-hydro

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43

Babiker, Musa E. Mohamed, Ahmed A. Alzharani, and Ayyob M. Bakry. "Computational Study of the Keto-Enol Tautomerism of 3-Phenyl-2,4-Pentanedione in the Gaseous Phase and Solvents Using DFT Methods." Oriental Journal Of Chemistry 39, no. 1 (2023): 40–46. http://dx.doi.org/10.13005/ojc/390105.

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The study of tautomerics equilibria is of vital importance as tautomeric compounds reactivity highly depends on the proportion of each tautomer. Herein, the tautomeric equilibrium of the 3-phenyl-2,4-pentanedione was studied theoretically by the b3lyp/6-31+g(d)methods. The effect of four solvents was considered (water, methanol, carbon tetrachloride and Cyclohexane).The tautomeric equilibrium takes place through four-membered ring transition state. The barrier heights energies of the tautomerics equilibria reaction of the transition state with reference to Keto were found to be 31.26, 31.23, 3

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44

Bihdan, O. A., and N. A. Alk Khalaf. "DFT-analysis of protolytic equivalents of 5-(aryl)-4-(methyl,amino)-1,2,4-triazole-3(2H)-thione." Current issues in pharmacy and medicine: science and practice 15, no. 2 (2022): 133–39. http://dx.doi.org/10.14739/2409-2932.2022.2.254474.

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The use of modern computer methods in aspects of quantum chemistry and systematic analysis of their results give an idea of the reactivity of organic compounds, as well as to understand the essence of known experimental data, correct predictions, and quantitative estimates. Undoubtedly, theoretical calculations are useful in solving such an urgent problem of modern chemistry as prototropic equilibria and properties of substances in the gas phase, solutions, and solid-state. The aim of the work – until recently assigned to a theoretical vivification in the infusion of solvents on tautomeric equ

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45

Szczepaniak, K., M. Szczesniak, W. Szajda, W. B. Person, and J. Leszczynski. "Infrared spectra of tautomers and rotamers of 9-methylguanine. An experimental and theoretical study." Canadian Journal of Chemistry 69, no. 11 (1991): 1705–20. http://dx.doi.org/10.1139/v91-251.

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Both amino-oxo and amino-hydroxy tautomeric forms of 9-methylguanine have been identified in approximately equal abundance in. infrared studies of these molecules isolated in the hydrophobic environment of an argon matrix at 12 K. The amino-hydroxy tautomer occurs in two different rotamers correlated with the rotation of the OH group. The ratio of concentrations of the two rotamers is sensitive to UV irradiation, and this ratio then relaxes to an equilibrium value after irradiation is stopped. This sensitivity allows us to separate the experimental spectra related to the oxo tautomer and to ea

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46

Hansen, Poul Erik. "NMR of Natural Products as Potential Drugs." Molecules 26, no. 12 (2021): 3763. http://dx.doi.org/10.3390/molecules26123763.

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This review outlines methods to investigate the structure of natural products with emphasis on intramolecular hydrogen bonding, tautomerism and ionic structures using NMR techniques. The focus is on 1H chemical shifts, isotope effects on chemical shifts and diffusion ordered spectroscopy. In addition, density functional theory calculations are performed to support NMR results. The review demonstrates how hydrogen bonding may lead to specific structures and how chemical equilibria, as well as tautomeric equilibria and ionic structures, can be detected. All these features are important for biolo

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47

Jawhar, Zanko S., Hiwa O. Ahmed, Asmaa A. Haydar, Halala A. Abdullah, and Sawza A. Mahamad. "One-Pot Synthesis, Pharmacological Evaluation, Docking Study, and DFT Calculations for Selected Imidazolidine-2,4-Diones." Science Journal of University of Zakho 6, no. 4 (2018): 150–54. http://dx.doi.org/10.25271/sjuoz.2018.6.4.541.

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The title compounds with different 5-substituted imidazolidine-2,4-dione were synthesized through a solvent-free reaction. Imidazolidine-2,4-dione derivatives are found to be an active pharmacophore for design and development of various bioactive lead compounds. Positive values of energy obtained for compound 1and 3, while a negative value for compound 2 was calculated by DFT in Gaussian. keto-enol tautomerism was supported by energy values and indicated the most stable tautomeric form. The biological evaluation has been supported by docking studies using molecular operating environment progra

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48

Zaharieva, Lidia, Ivan Angelov, and Liudmil Antonov. "Stationary External Electric Field—Mimicking the Solvent Effect on the Ground-State Tautomerism and Excited-State Proton Transfer in 8-(Benzo[d]thiazol-2-yl)quinolin-7-ol." Molecules 29, no. 15 (2024): 3506. http://dx.doi.org/10.3390/molecules29153506.

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The effect of the external electric field on the ground-state tautomerism in 8-(benzo[d]thiazol-2-yl)quinolin-7-ol has been studied by using density functional theory. The compound exists as an enol tautomer (off state) and under the influence of the external electric field a long-range intramolecular proton transfer can occur, placing the tautomeric proton at the quinolyl nitrogen atom (on state). This is a result of the much higher dipole moment of the end keto tautomer and indicates that the external electric field can be used to mimic the implicit solvent effect in tautomeric systems. In t

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49

Jafari Rad, Azadeh, Maryam Abbasi, and Bahareh Zohrevand. "Iron Chelation by thiocytosine: Investigating electronic and structural features for describing tautomerism and metal chelation processes." Main Group Chemistry 21, no. 1 (2022): 177–84. http://dx.doi.org/10.3233/mgc-210110.

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This work was performed regarding the importance of iron (Fe) chelation for biological systems. This goal was investigated by assistance of a model of thiocytosine (TC) for participating in Fe-chelation processes. First, formations of tautomeric conformations were investigated to explore existence of possible structures of TC. Next, Fe-chelation processes were examined for all four obtained tautomers of TC. The results indicated that thiol tautomers could be seen at higher stability than thio tautomers, in which one of such thiol tautomers yielded the strongest Fe-chelation process to build Fe

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50

Bunting, John W., James P. Kanter, Raymond Nelander та Zhennan Wu. "The acidity and tautomerism of β-diketones in aqueous solution". Canadian Journal of Chemistry 73, № 8 (1995): 1305–11. http://dx.doi.org/10.1139/v95-161.

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The acidity and keto–enol tautomerism of a series of symmetrical β-diketones (RCOCH2COR (1): R = methyl (a), phenyl (b), 3-pyridinyl (c), 4-pyridinyl (d), 3-(N-methyl)pyridinio (e), and 4-(N-methyl)pyridinio (f)) and two series of unsymmetrical β-diketones (RCOCH2COCH3 (7a–7f) and RCOCH2COC6H5 (8a–8f)) have been investigated in aqueous solution at 25 °C and ionic strength 0.1. Values of [Formula: see text] were measured spectrophotometrically, and the acidities of the enols [Formula: see text] were obtained from the analysis of the pH dependence of the buffer catalysis for the general acid-cat

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