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Journal articles on the topic 'Tautomer'

Author: Grafiati

Published: 4 June 2021

Last updated: 26 July 2025

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1

Qi, Luguang, Yanhui Jin, Huina Li, Yanpeng Dong, and Chuang Xie. "The Role of Solvent in Tautomer Solvate Crystallization: A Case of 6-Amino-1,3-Dimethyl-5-Nitrosouracil." Transactions of Tianjin University 26, no. 6 (2020): 458–69. http://dx.doi.org/10.1007/s12209-020-00247-7.

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Abstract Tautomers are structural isomers that readily interconvert and may exhibit different properties. The effect of solvent on tautomeric equilibria in solution has been a subject of some research. Tautomer solvate is less common, and the role of solvent in the crystallization of tautomer solvate remains an interesting topic. In this work, we used 6-amino-1,3-dimethyl-5-nitrosouracil (NAU) as the tautomeric model material, which can present in nitrone–enamine form (Tautomer A) or oxime–imine form (Tautomer B). A solvate with NAU/DMSO ratio of 1:1 was discovered and characterized using sing

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2

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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3

Cysewski, Piotr. "Theoretical Studies on the Tautomeric Properties of Diamino-5-formamidopyrimidines." Zeitschrift für Naturforschung C 53, no. 11-12 (1998): 1027–36. http://dx.doi.org/10.1515/znc-1998-11-1214.

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Abstract The results of theoretical geometry prediction of formamidopyrimidine(fapy)-adenine and fapy-guanine tautomers are presented. Among 54 potential tautomeric structures of fapy-adenine the most stable structure corresponds to the diamino-keto isomer. The solvent effect has insignificant influence on the fapy-adenine tautomers succession. The fapy-guanine has 172 potential isomers. There are three most stable tautomers of this guanine derivative, which may exchange the order depending on the polarity of the environment. In vapour the most probable is the 4-enol-6-keto-diamino tautomer, w

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4

Babu, Numbury Surendra, and Didugu Jayaprakash. "Computational Study of the Stability of Tautomers and equilibrium constants of Cyanuric acid (CA) in Different solvents." JOURNAL OF ADVANCES IN CHEMISTRY 11, no. 2 (2015): 3485–97. http://dx.doi.org/10.24297/jac.v11i2.6691.

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In the present investigation, the tautomeric and equilibrium of Cyanuric acid has been studied using Hartifock (HF) method in the gas phase and different solvents using the PCM model. The relative energies of these tautomers have been calculated at the HF level of theory using 6-311++ G (d,p) basis set. Energetics and relative stabilities of the tautomers were compared and analyzed in both the gaseous and different solvents. The results indicate that the keto tautomer (CA1) is the most stable form in the gas phase and other solvents. The order of stability of isomers was found to be CA1 > C

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5

Parisi, Emmanuele, and Roberto Centore. "Stabilization of an elusive tautomer by metal coordination." Acta Crystallographica Section C Structural Chemistry 77, no. 7 (2021): 395–401. http://dx.doi.org/10.1107/s2053229621006203.

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The solid-state isolation of the different tautomers of a chemical compound can be a challenging problem. In many cases, tautomers with an energy very close to the most stable one cannot be isolated (elusive tautomers). In this article, with reference to the 4-methyl-7-(pyrazin-2-yl)-2H-[1,2,4]triazolo[3,2-c][1,2,4]triazole ligand, for which the elusive 3H-tautomer has an energy only 1.4 kcal mol−1 greater than the most stable 2H form, we show that metal complexation is a successful and reliable way for stabilizing the elusive tautomer. We have prepared two complexes of the neutral ligand with

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6

Rybczyński, Patryk, Anna Kaczmarek-Kędziera, Alex Iglesias-Reguant, Damian Plażuk, and Borys Ośmiałowski. "Tautomeric Equilibrium in 1-Benzamidoisoquinoline Derivatives." Molecules 28, no. 3 (2023): 1101. http://dx.doi.org/10.3390/molecules28031101.

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In this study, the tautomeric equilibrium of a sequence of 1-benzamidoisoquinoline derivatives was investigated with the tools of NMR spectroscopy and computational chemistry. The equilibrium between different tautomers in these systems could be controlled via the substitution effect, and the relative content of the amide form varied from 74% for the strong electron-donating NMe2 substituent to 38% for the strong electron-accepting NO2 group in the phenyl ring. In contrast to the previously investigated 2-phenacylquinoline derivatives, the most stable and thus most abundant tautomer in the 1-b

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7

Li, Xiaozhou, Andrew D. Bond, Kristoffer E. Johansson, and Jacco Van de Streek. "Distinguishing tautomerism in the crystal structure of (Z)-N-(5-ethyl-2,3-dihydro-1,3,4-thiadiazol-2-ylidene)-4-methylbenzenesulfonamide using DFT-D calculations and13C solid-state NMR." Acta Crystallographica Section C Structural Chemistry 70, no. 8 (2014): 784–89. http://dx.doi.org/10.1107/s2053229614015356.

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The crystal structure of the title compound, C11H13N3O2S2, has been determined previously on the basis of refinement against laboratory powder X-ray diffraction (PXRD) data, supported by comparison of measured and calculated13C solid-state NMR spectra [Hanganet al.(2010).Acta Cryst.B66, 615–621]. The molecule is tautomeric, and was reported as an amine tautomer [systematic name:N-(5-ethyl-1,3,4-thiadiazol-2-yl)-p-toluenesulfonamide], rather than the correct imine tautomer. The protonation site on the molecule's 1,3,4-thiadiazole ring is indicated by the intermolecular contacts in the crystal s

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8

ABIRAM, A., and P. KOLANDAIVEL. "INTERACTION OF THE TAUTOMERIC STATES OF HISTIDINE WITH Cu AND Zn METAL IONS – A THEORETICAL STUDY." Journal of Theoretical and Computational Chemistry 08, no. 04 (2009): 657–76. http://dx.doi.org/10.1142/s021963360900499x.

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A density functional study on the interaction of Cu 2+ and Zn 2+ metal ions at the predominant positions of N τ– H and N π– H histidine tautomers has been performed. The fully optimized energy of the isolated histidine tautomers at B3LYP/6-311++G** level of theory depicts N τ– H tautomer to be much stable compared to that of the N π– H tautomer. The interaction of metal ions forms bidentate and tridentate complexes with N τ– H tautomer, while it is absent in the case of N π– H tautomer emphasizing the role of former in structural determination of liganated proteins. The Zn 2+ ion induces a bar

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9

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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10

Zilberg, Shmuel, and Bernhard Dick. "Less stable tautomers form stronger hydrogen bonds: the case of water complexes." Physical Chemistry Chemical Physics 19, no. 36 (2017): 25086–94. http://dx.doi.org/10.1039/c7cp04105e.

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Hydrogen bonding in cyclic complexes of water with tautomeric pairs of molecules M<sup>0</sup> and M<sup>1</sup> is calculated to be stronger by more than 25% for the less stable tautomer M<sup>1</sup> in all cases where the energy gap between the two tautomers is large (ΔE(M<sup>0</sup> − M<sup>1</sup>) > 10 kcal mol<sup>−1</sup>).

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11

Oziminski, Wojciech Piotr, and Igor Wiśniewski. "Quantum-chemical study on the relative stability of sildenafil tautomers." Structural Chemistry 32, no. 5 (2021): 1733–43. http://dx.doi.org/10.1007/s11224-021-01818-7.

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AbstractThe tautomeric equilibrium of sildenafil molecule was theoretically studied using B3LYP and M06-2X density functional theory (DFT) methods in connection with aug-cc-pVDZ correlation consistent basis set. Calculations were performed for gas phase and water solution conditions modelled by polarizable continuum model (PCM). Three tautomeric forms are possible. Two keto forms: A — where the tautomeric proton in more distant from carbonyl group and B — where it is closer, and one enol form denoted, C. Both DFT methods qualitatively give similar tautomer stability order: B > A > C. The

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12

JIMÉNEZ-PULIDO, SONIA B., NURIA A. ILLÁN-CABEZA, FRANCISCO HUESO-UREÑA, and MIGUEL N. MORENO-CARRETERO. "TAUTOMERISM IN NEUTRAL AND DEPROTONATED 6-AMINO-5-FORMYLURACILS: A PM3-COSMO APPROACH." Journal of Theoretical and Computational Chemistry 12, no. 05 (2013): 1350032. http://dx.doi.org/10.1142/s0219633613500326.

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In order to identify the structure of the most stable tautomers of 6-amino-5-formyluracil and its N-methylated derivatives in different pH conditions, relative stabilities of potential tautomers in aqueous phase have been calculated taking into account the entropy effects over the tautomeric equilibria. In each medium, the tautomer with lower energy must be the most representative form at the corresponding pH and the knowledge of the effect of the medium in the tautomerization energies allows evaluating the possible effect of the medium over the molecular stability. The results show that, in a

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13

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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14

Brewer, Greg, Cynthia Brewer, Raymond J. Butcher, and Peter Zavalij. "Selective Generation of Aldimine and Ketimine Tautomers of the Schiff Base Condensates of Amino Acids with Imidazole Aldehydes or of Imidazole Methanamines with Pyruvates—Isomeric Control with 2- vs. 4-Substituted Imidazoles." Molecules 29, no. 6 (2024): 1324. http://dx.doi.org/10.3390/molecules29061324.

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The Schiff base condensation of 5-methyl-4-imidazole carboxaldehyde, 5Me4ImCHO, and the anion of an amino acid, H2N-CH(R)CO2− (R = -CH3, -CH(CH3)2 and -CH2CH(CH3)2), gives the aldimine tautomer, Im-CH=N-CH(R)CO2−, while that of 5-methylimidazole-4-methanamine, 5MeIm-4-CH2NH2, with a 2-oxocarboxylate anion, R-C(O)-CO2−, gives the isomeric ketimine tautomer, Im-CH2-N=C(R)CO2−. All are isolated as the neutral nickel(II) complexes, NiL2, and are characterized by single crystal structure determination, IR, and positive ion ESI MS. In the cases of the 4 substituted imidazoles, either 5MeIm-4-CHO or

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15

Conrad, Marcus, Anselm H. C. Horn, and Heinrich Sticht. "Computational Analysis of Histamine Protonation Effects on H1R Binding." Molecules 28, no. 9 (2023): 3774. http://dx.doi.org/10.3390/molecules28093774.

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Despite numerous studies investigating histamine and its receptors, the impact of histamine protonation states on binding to the histamine H1-receptor (H1R) has remained elusive. Therefore, we assessed the influence of different histamine tautomers (τ-tautomer, π-tautomer) and charge states (mono- vs. dicationic) on the interaction with the ternary histamine-H1R-Gq complex. In atomistic molecular dynamics simulations, the τ-tautomer formed stable interactions with the receptor, while the π-tautomer induced a rotation of the histamine ring by 180° and formed only weaker hydrogen bonding interac

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16

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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17

Bax, Ben, Chun-wa Chung, and Colin Edge. "Getting the chemistry right: protonation, tautomers and the importance of H atoms in biological chemistry." Acta Crystallographica Section D Structural Biology 73, no. 2 (2017): 131–40. http://dx.doi.org/10.1107/s2059798316020283.

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There are more H atoms than any other type of atom in an X-ray crystal structure of a protein–ligand complex, but as H atoms only have one electron they diffract X-rays weakly and are `hard to see'. The positions of many H atoms can be inferred by our chemical knowledge, and such H atoms can be added with confidence in `riding positions'. For some chemical groups, however, there is more ambiguity over the possible hydrogen placements, for example hydroxyls and groups that can exist in multiple protonation states or tautomeric forms. This ambiguity is far from rare, since about 25% of drugs hav

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18

CHARIF, I. E., S. M. MEKELLECHE, and D. VILLEMIN. "SOLVENT EFFECTS ON THE KETO-ENOL TAUTOMERIC EQUILIBRIUM OF TETRONIC AND ETHYL ACETOACETATE CARBON ACIDS: A THEORETICAL STUDY." Journal of Theoretical and Computational Chemistry 09, no. 06 (2010): 1021–32. http://dx.doi.org/10.1142/s0219633610006171.

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The solvent effects on the keto-enol tautomeric equilibriums of ethyl acetoacetate (EAA) and tetronic acid (TA) are theoretically investigated. The present study shows that the most stable keto tautomer of EAA corresponds to the trans diketo, E, Z form; while the most stable enol tautomer corresponds to the structure in which the enolization takes place at the carbonyl group. Our calculations also put in evidence that the keto tautomer of TA prefers the trans diketo, E, E form, while the most stable enol tautomer corresponds to the structure in which the enolization takes place at the carbonyl

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19

Venkatachalam, T. K., Gregory K. Pierens, and David Reutens. "Synthesis and Characterization of Anils Exhibiting Thermochromism." Australian Journal of Chemistry 63, no. 8 (2010): 1272. http://dx.doi.org/10.1071/ch09579.

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Several Schiff bases containing a hydroxy naphthyl moiety and substituted pyridyl groups were synthesized. The pyridyl substituted Schiff bases were isolated as a single stable tautomer at room temperature. High-resolution proton and carbon NMR spectroscopy showed that these compounds exist as keto tautomers. The Schiff bases showed extraordinary stability and did not convert to the enol tautomer, even at high temperatures. Most of the compounds exhibited thermochromic properties.

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20

Raczyńska, Ewa D., Katarzyna Zientara, Tomasz M. Stępniewski та Katarzyna Kolczyńska. "Stability, polarity, intramolecular interactions and π-electron delocalization for all eighteen tautomers rotamers of uracil. DFT studies in the gas phase". Collection of Czechoslovak Chemical Communications 74, № 1 (2009): 57–72. http://dx.doi.org/10.1135/cccc2008149.

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Complete tautomeric equilibria were investigated for uracil at the DFT(B3LYP)/6-311+G(d,p) level to establish the stability order of all possible 18 tautomers-rotamers in the gas phase and to characterize their internal effects, polarity and aromatic character. Although the di-NH form strongly predominates (100%) in the mixture, the NH–OH, di-OH and CH–NH forms can be also considered. The favored tautomer is moderately stabilized by intramolecular interactions (attractions of the NH and C=O groups); it is also moderately polar and moderately delocalized. Stability of the functional groups (bot

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21

Pasca, Roxana-Diana, Atena Moldovan, Ossi Horovitz, and Alexandru Lupan. "On the thermodynamics of triazines. A DFT and topological study." International Journal of Computational Physics Series 1, no. 1 (2018): 12. http://dx.doi.org/10.29167/a1i1p12.

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Tautomerism is the relation between isomeric organic compounds, which readily interconvert, usually by relocation of a proton. It plays an important role in the biological activity of compounds. In the series of tautomeric triazines (monoxime and dioxime derivatives) energy computations have been performed. The results have shown that for the monoxime, the amino keto tautomer is favored by 10.9 kJ/mol vs. the enol form; for the dioxime tautomer, the imino keto form is 17.6 kJ/mol lower in energy in comparison with the most stable amino keto tautomer. Topological aspects have been considered. C

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22

Albright, Abigail L., Lucy Collins, John Li, Benjamin Harris, and Jonathan M. White. "Crystal Structures of the Amide and Iminol Tautomers O-(3,5-dinitrobenzoyloxy)benzohydroxamate. A Case of a Disappearing Solvate?" Australian Journal of Chemistry 69, no. 10 (2016): 1193. http://dx.doi.org/10.1071/ch16369.

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The O-(3,5-dinitrobenzoyl) derivative of benzohydroxamic acid 1 crystallizes in its iminol tautomeric form, hydrogen bonded to a molecule of dimethyl sulfoxide (DMSO) when crystallized from methanol in the presence of DMSO. In contrast, in the absence of DMSO, 1 crystallizes in its amide tautomeric form. Computations suggest that in the absence of DMSO, the amide tautomer of 1 is significantly more stable than the iminol form. Conversely, in the presence of DMSO, the two forms have comparable stabilities. Solution infrared spectra of 1 run in dichloromethane are consistent with the amide tauto

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23

CHONG, DELANO P. "DENSITY FUNCTIONAL THEORY STUDY OF THE PHOTOELECTRON SPECTRA OF 5-METHYLTETRAZOLE." Journal of Theoretical and Computational Chemistry 12, no. 01 (2013): 1250096. http://dx.doi.org/10.1142/s0219633612500964.

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The molecule 5-methyltetrazole (5MTZ) can exist in two taumeric forms. The vertical ionization energies (VIEs) of both valence and core electrons of both the tautomers are calculated with our established DFT procedures and compared with available experimental data. For the 2H-tautomer, the average absolute deviations (AADs) for the outer-valence VIEs and core-electron binding energies (CEBEs) from experiment are below 0.1 eV, while the AAD for the inner-valence VIEs is much larger at 0.4 eV. For the 1H-tautomer, no observed valence VIEs have been reported and the AAD for the calculated CEBEs i

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24

Hall, Victoria M., Jeffery A. Bertke, and Jennifer A. Swift. "Two tautomeric forms of 2-amino-5,6-dimethylpyrimidin-4-one." Acta Crystallographica Section C Structural Chemistry 72, no. 6 (2016): 460–64. http://dx.doi.org/10.1107/s2053229616007403.

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Derivatives of 4-hydroxypyrimidine are an important class of biomolecules. These compounds can undergo keto–enol tautomerization in solution, though a search of the Cambridge Structural Database shows a strong bias toward the 3H-keto tautomer in the solid state. Recrystallization of 2-amino-5,6-dimethyl-4-hydroxypyrimidine, C6H9N3O, from aqueous solution yielded triclinic crystals of the 1H-keto tautomer, denoted form (I). Though not apparent in the X-ray data, the IR spectrum suggests that small amounts of the 4-hydroxy tautomer are also present in the crystal. Monoclinic crystals of form (II

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25

Al-Omari, Hamzeh S. M. "Semiempirical Method MNDO for the Evaluation of the Effect of Different Substituents at the Imine-Carbon Position on the Acetaldemine-Vinylamine Tauotomerization and Comparison to the Substitution at α-Position". Zeitschrift für Naturforschung A 59, № 12 (2004): 987–96. http://dx.doi.org/10.1515/zna-2004-1218.

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MNDO calculations have been employed to study the effect of some substituents of the acetaldemine-vinylamine tautomeric system at the imine-carbon position of CH3CXNH, where X = H, F, CN, NH2, NO2, BH2, CH3 and CF3. It is found that the substitutents F, NH2 and NO2 encourage the formation of the enamine tautomer. The substitutents CN, CH3, CF3 and BH2 encourage the formation of the imine tautomer. Isodesmic reactions, free energy change (ΔG), charge distribution and energy gap (Eg) between HOMO and LUMO were used to prove these findings. Resonance stabilization was a major factor in the determ

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26

García-Báez, Efrén V., Itzia I. Padilla-Martínez, Alejandro Cruz, and Martha C. Rosales-Hernández. "13C-NMR Chemical Shifts in 1,3-Benzazoles as a Tautomeric Ratio Criterion." Molecules 27, no. 19 (2022): 6268. http://dx.doi.org/10.3390/molecules27196268.

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Benzimidazole is an important heterocyclic fragment, present in many biologically active compounds with a great variety of therapeutic purposes. Most of the benzimidazole activities are explained through the existence of 1,3-tautomeric equilibrium. As the binding affinity of each tautomer to a protein target depends on an established bioactive conformation, the effect of tautomers on the ligand protein binding mechanism is determinant. In this work, we searched and analyzed a series of reported 13C-NMR spectra of benzazoles and benzazolidine-2-thiones with the purpose of estimating their tauto

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27

Dobosz, Robert, and Ryszard Gawinecki. "Quantum chemical prediction of structure and stability of the benzodihydropyrimidine tautomers." Journal of Theoretical and Computational Chemistry 13, no. 07 (2014): 1450056. http://dx.doi.org/10.1142/s0219633614500564.

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B3LYP/maug-cc-pVTZ and MP2/maug-cc-pVTZ calculations show that 3,4-dihydro-quinazoline and its 2- and/or 4-methyl and -phenyl substituted derivatives in solution (chloroform, DMSO, methanol) are only by 0.3 kcal/mol–2.2 kcal/mol more stable than the respective tautomeric 1,4-dihydroquinazolines (the available literature experimental stability data are not coherent). In the gas phase, 2- and/or 4-substituted tautomers of 3,4-dihydroquinazoline are also energetically preferred (B3LYP/maug-cc-pVTZ, MP2/maug-cc-pVTZ and CCSD/cc-pVDZ calculations lead to the same conclusion). In vacuum, 1,4-dihydro

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28

Skotnicka, Agnieszka, Przemysław Czeleń, and Ryszard Gawinecki. "Tautomeric Equilibria in Solutions of 2-Phenacylbenzimidazoles." Heteroatom Chemistry 2019 (February 3, 2019): 1–9. http://dx.doi.org/10.1155/2019/4364207.

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Detailed NMR spectral analysis of DMSO-d6 solutions of the series of substituted 2-phenacylbenzimidazoles (ketimine form, K) reveals two from three tautomeric forms. Integrals of the 1H NMR signals are used in establishing the molar ratio of tautomers. The experimental analyses are supported by quantum-chemical calculations, which satisfactorily reproduced the experimental trends. Although the reported semiempirical quantum-chemical calculations show that enaminone E, i.e., 2-(1,3-dihydro-2H-benzo[d]imidazol-2-ylidene)-1-phenylethan-1-one, was thermodynamically most stable, the results of MP2

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29

Tykhanov, Dmytro, Irina Serikova, Fedor Yaremenko, and Alexander Roshal. "Structure and spectal properties of cinnamoyl pyrones and their vinylogs." Open Chemistry 8, no. 2 (2010): 347–55. http://dx.doi.org/10.2478/s11532-009-0138-4.

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AbstractThe 1H-NMR and quantum chemical analysis of the stability of tautomers of cinnamoyl pyrone derivatives and vinylogs has been studied. The relationship between the structure of the most stable tautomer and its spectral properties has been investigated. It has been determined that the tautomer of highest stability (88–100 molar %) has an α-pyrone structure and exhibits a trans-conformation in the cinnamoyl fragment. An intense fluorescence of dyes has been observed in non-polar solvents with cinnamoyl fragments having electron-donating substituents or several double bonds in the polymeth

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30

Secrieru, Alina, Susy Lopes, Maria L. S. Cristiano, and Rui Fausto. "Structure and IR Spectra of 3(5)-Aminopyrazoles and UV-Induced Tautomerization in Argon Matrix." Molecules 26, no. 14 (2021): 4299. http://dx.doi.org/10.3390/molecules26144299.

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The prototropic tautomerism in 3(5)-aminopyrazoles was investigated by matrix isolation infrared (IR) spectroscopy, supported by DFT(B3LYP)/6-311++G(d,p) calculations. In consonance with the experimental data, the calculations predict tautomer 3-aminopyrazole (3AP) to be more stable than the 5-aminopyrazole (5AP) tautomer (calculated energy difference: 10.7 kJ mol−1; Gibbs free energy difference: 9.8 kJ mol−1). The obtained matrix isolation IR spectra (in both argon and xenon matrices) were interpreted, and the observed bands were assigned to the tautomeric forms with help of vibrational calcu

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31

Hureau, Matthieu, Alain Moissette, and Konstantin Smirnov. "A Spectroscopic Study of Tautomeric Equilibrium of Salicylideneaniline in ZSM-5 Zeolites." Molecules 24, no. 4 (2019): 795. http://dx.doi.org/10.3390/molecules24040795.

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Salicylideneaniline (SA) sorbed in cation-exchanged M-ZSM-5 (M = H+, Li+, Na+, K+, Rb+, Cs+ and Zn2+) zeolites was studied by spectroscopic techniques assisted by quantum-chemical calculations. The nature of extra-framework cations present in the zeolite void was found to affect the spectral signature of the sorbed SA molecule that points to the shift of tautomeric equilibrium between the enol and keto forms. Small size cations, such as H+ and Li+, stabilize a cis-keto SA tautomer along with a enol one in the zeolite structure. The calculations indicate that the sorbed cis-keto tautomer may ha

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32

Sanders, Robert A., David V. Zyzak, Thomas R. Morsch, and George P. Rizzi. "Elucidation of Tautomer Structures of 2-Acetyltetrahydropyridine Using Gas Chromatography/Mass Spectrometry and Gas Chromatography/Infrared Spectroscopy." European Journal of Mass Spectrometry 11, no. 2 (2005): 217–20. http://dx.doi.org/10.1255/ejms.703.

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2-Acetyltetrahydropyridine is an important flavor component in heated corn products such as popcorn and corn chips. The compound exists as a mixture of two tautomers that have different flavor/aroma characteristics. The tautomers also exhibit different chromatographic behaviors and are distinguishable spectroscopically. Alhough their electron ionization mass spectra are different, structure assignment based on low-resolution mass spectra alone has been subject to error. A combination of high resolution exact mass measurement and vapor phase infrared measurement of the separated tautomers was u

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33

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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34

Paskaleva, Vesselina, Stefan Dobrev, Nikolay Kochev, Silvia Angelova, and Liudmil Antonov. "Unusual Para-Substituent Effects on the Intramolecular Hydrogen Bond in Hydrazone-Based Switches: Insights from Chemical Landscape Analysis and DFT Calculations." Physchem 1, no. 2 (2021): 189–201. http://dx.doi.org/10.3390/physchem1020013.

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Тhe adequacy of chemical property predictions strongly depends on the structure representation, including the proper treatment of the tautomeric and isomeric forms. A combination of an in-house developed open-source tool for automatic generation of tautomers, Ambit-Tautomer, based on H-atom shift rules and standard quantum chemical (DFT) calculations is used for a detailed investigation of the possible geometric isomers, conformers and tautomers of unsubstituted and para-substituted phenylhydrazones, systems with experimentally observed unusual para-substituent effects on the intramolecular hy

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35

Chitsazi, Rezvan, Phillip W. Gingrich, James P. Long, Chong Wu, and Bissan Al-Lazikani. "Abstract 4460: OpencanSARchem: chemistry registration and standardization pipeline for FAIR integration of bioassay data." Cancer Research 85, no. 8_Supplement_1 (2025): 4460. https://doi.org/10.1158/1538-7445.am2025-4460.

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Abstract Introduction: The rapid growth of medicinal chemistry and bioactivity data has driven AI advancements but inconsistencies in chemical representation across databases make bioactivity-focused data integration challenging. Tautomerism, a key challenge, complicates chemical registration due to the existence of multiple interchangeable molecular forms, significantly impacting database uniqueness and separating bioactivity data across tautomeric forms. We previously developed a standalone, fully deployable solution to address these challenges (Dolciami et al. 2022), now a core component of

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36

Roggen, Heidi, Lars Bohlin, Robert Burman, et al. "2-Substituted agelasine analogs: Synthesis and biological activity, and structure and reactivity of synthetic intermediates." Pure and Applied Chemistry 83, no. 3 (2011): 645–53. http://dx.doi.org/10.1351/pac-con-10-09-25.

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2-Substituted N-methoxy-9-methyl-9H-purin-6-amines were synthesized either from their corresponding 6-chloro-9-methyl-9H-purines or 2-chloro-N-methoxy-9-methyl-9H-purin-6-amine. Great diversity in the amino/imino tautomeric ratios was observed and calculated based on 1H NMR. The tautomers were identified by 1D and 2D 1H, 13C, and 15N NMR techniques, and showed significant variation both in 13C and 15N shift values. Comparison of the tautomeric ratios with Hammett F values revealed that as the field/inductive withdrawing abilities of the 2-substituent increased, the ratio of amino:imino tautome

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37

Shabanian, Meisam, Hassan Moghanian, Mohsen Hajibeygi, and Azin Mohamadi. "Theoretical Investigation of Solvation Effects on the Tautomerism of Maleic Hydrazide." E-Journal of Chemistry 9, no. 1 (2012): 107–12. http://dx.doi.org/10.1155/2012/976161.

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A DFT study is used to calculate structural data of tautomers of maleic hydrazide (MH) in the gas phase and selected solvents such as benzene (non-polar solvent), tetrahydrofuran (polar aprotic solvent) and methanol (protic solvent), dimethyl sulfoxide (polar aprotic solvent) and water (protic solvent) using PCM model. All tautomers are optimized at the B3LYP/6−31++G(d,p). The results show that the tautomer MH2except in methanol is more stable than the other tautomers but in methanol MH5(Diol) is more stable. In addition, stability of the tautomers in deferent solvents shows interesting result

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38

Rzepiela, Kacper, Aneta Buczek, Teobald Kupka, and Małgorzata A. Broda. "On the aromaticity of uracil and its 5-halogeno derivatives as revealed by theoretically derived geometric and magnetic indexes." Structural Chemistry 32, no. 1 (2020): 275–83. http://dx.doi.org/10.1007/s11224-020-01682-x.

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AbstractThe problem of aromaticity in heterocyclic rings of uracil and its 5-halogenoderivatives (5XU) was analyzed theoretically by calculating modified harmonic oscillator model of aromaticity (HOMA) for Heterocycle Electron Delocalization (HOMHED), nucleus-independent chemical shift parameters (NICS) and the so-called scan experiments, using helium-3 atom as a magnetic probe. The impact of halogen electronegativity on C5 atom’s NBO charges was also investigated. Water, as a polar environment, has a negligible impact on 5XU aromaticity. The most stable diketo tautomer shows a very low aromat

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39

Grollau, F., E. Mengesha, J. M. Mestdagh, et al. "The 4(5)-methylimidazole System in the gas phase: Insights from helium droplet experiment vs. quantum chemistry." Low Temperature Physics 51, no. 4 (2025): 444–52. https://doi.org/10.1063/10.0036203.

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The two tautomers of 4(5)-methylimidazole are sufficiently similar, making it challenging to accurately measure their intrinsic relative abundance. In this study, we present a method for such a measurement in the gas phase, which involves sublimation of the tautomers in an unknown ratio before they are trapped in a helium nanodroplet at 0.4 K. The tautomers are then identified thanks to infrared absorption of their N–H stretching mode using the HENDI (HElium Nanodroplet Isolation) technique. These results, which find that 4-methylimidazole is the predominant tautomer, are compared with quantum

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40

Hush, NS, MK Livett, JB Peel, and GD Willett. "Variable-Temperature Ultraviolet Photoelectron-Spectroscopy of the Keto-Enol Tautomers of Pentane-2,4-Dione." Australian Journal of Chemistry 40, no. 3 (1987): 599. http://dx.doi.org/10.1071/ch9870599.

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The HeI photoelectron spectra of pentane-2,4-dione measured at various temperatures have been subjected to a spectrum-stripping technique to enable isolation of the complete HeI photoelectron spectra of the keto and enol tautomers. The resulting spectrum-stripping coefficients allow evaluation of the enolization equilibrium constant at each temperature and subsequently the enthalpy of enolization. Interpretation of the photoelectron spectra is achieved with the use of ab initio molecular orbital calculations. Photoionization of non-bonding oxygen, and π -type electrons, contribute to the low i

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41

Ruaysap, Makabodee, Stuart R. Kennedy, Collin M. Mayhan, et al. "Novel keto–enol tautomerism in 1,3,5-trihydroxybenzene systems." Chemical Communications 56, no. 85 (2020): 12985–88. http://dx.doi.org/10.1039/d0cc03639k.

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We report a new synthesis of the water-soluble compound 1,3,5-trihydroxy-2,4,6-trimethylsulfonic acid (1), which exists in two tautomeric forms (60 : 40::enol%:keto%), and its lanthanide complexes. Relative tautomer stability is influenced by intramolecular H-bonding and competing implicit solvent effects.

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42

Ryabov, Mikhail A., Thi Ngok Anh Vu, Olga V. Kovalchukova, and Dmitry S. Gusarov. "Quantum-chemical modeling of structure and properties of nitrogen derivatives of phloroglucinol." Butlerov Communications 57, no. 3 (2019): 51–57. http://dx.doi.org/10.37952/roi-jbc-01/19-57-3-51.

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The DFT/B3LYP quantum-chemical method has been used to simulate the structure of 2-((2-hydroxyphenyl) diazonyl) benzene-1,3,5-triol (L1) and 2-((2-hydroxy-4-nitrophenyl) diazonyl) benzene-1,3,5-triol (L2) molecules. The spatial and electronic structure of molecules in various tautomeric forms was determined. It was shown that the stability of these compounds is primarily due to the presence of strong intramolecular hydrogen bonds (IHB), which form six-membered cycles, and the isomerism of the molecule, which assume the formation of IHB. The structures where IHB form five-membered cycles, are l

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43

Hamidian, Kourosh, Mohsen Irandoust, Ezzat Rafiee, and Mohammad Joshaghani. "Synthesis, Characterization, and Tautomeric Properties of Some Azo-azomethine Compounds." Zeitschrift für Naturforschung B 67, no. 2 (2012): 159–64. http://dx.doi.org/10.1515/znb-2012-0208.

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The primary azo compound 1-(3-formyl-4-hydroxyphenylazo)-4-nitrobenzene reacts with some aliphatic and aromatic diamines and yields the corresponding azo-azomethine compounds. These compounds were characterized by elemental analysis, IR, UV/Vis, and NMR spectroscopy. The primary azo compound exists entirely in the azo form in solution as well as in the solid phase. The tautomeric structure of azo-azomethine compounds heavily depends on the solvent and the substituents. Aliphatic diamine-based compounds favor the enol-imine tautomer while aromatic diamine-based compounds have structures that li

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44

Georgiev, Anton, and Liudmil Antonov. "8-(Pyridin-2-yl)quinolin-7-ol as a Platform for Conjugated Proton Cranes: A DFT Structural Design." Micromachines 11, no. 10 (2020): 901. http://dx.doi.org/10.3390/mi11100901.

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Theoretical design of conjugated proton cranes, based on 7-hydroxyquinoline as a tautomeric sub-unit, has been attempted by using ground and excited state density functional theory (DFT) calculations in various environments. The proton crane action request existence of a single enol tautomer in ground state, which under excitation goes to the excited keto tautomer through a series of consecutive excited-state intramolecular proton transfer (ESIPT) steps with the participation of the crane sub-unit. A series of substituted pyridines was used as crane sub-units and the corresponding donor-accept

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45

Rae, AD, CG Ramsay, and PJ Steel. "Heterocyclic Tautomerism. IV. The Solution and Crystal Structures of 1-Aryl-3-phenyl-1,2,4-triazol-5-ones." Australian Journal of Chemistry 41, no. 4 (1988): 419. http://dx.doi.org/10.1071/ch9880419.

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The title compounds are shown to exist in solution and in the solid state as 4H-tautomers. X-Ray crystal structure determinations show that 1,3-diphenyl-1,2,4-triazol-5-one exists as a dimeric pair of strongly hydrogen-bonded molecules and that 3-phenyl-1-(2-pyridyl)-1,2,4- triazol-5-one exists as the 4H-tautomer stabilized by a complex network of hydrogen bonding to water molecules.

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46

Bekö, Sándor L., Silke D. Thoms, Martin U. Schmidt, and Michael Bolte. "Tizanidine and tizanidine hydrochloride: on the correct tautomeric form of tizanidine." Acta Crystallographica Section C Crystal Structure Communications 68, no. 1 (2011): o28—o32. http://dx.doi.org/10.1107/s0108270111052012.

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A crystallization series of tizanidine hydrochloride, used as a muscle relaxant for spasticity acting centrally as an α2-adrenergic agonist, yielded single crystals of the free base and the hydrochloride salt. The crystal structures of tizanidine [systematic name: 5-chloro-N-(imidazolidin-2-ylidene)-2,1,3-benzothiadiazol-4-amine], C9H8ClN5S, (I), and tizanidine hydrochloride {systematic name: 2-[(5-chloro-2,1,3-benzothiadiazol-4-yl)amino]imidazolidinium chloride}, C9H9ClN5S+·Cl−, (II), have been determined. Tizanidine crystallizes with two almost identical molecules in the asymmetric unit (r.m

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47

Kudrya, V. Yu, V. M. Yashchuk, A. P. Naumenko, Y. Mely, and Ya O. Gumenyuk. "Low-Temperature Luminescent Studies of Emissive Guanine Substitute for the Detection of Biopolymers." Ukrainian Journal of Physics 65, no. 4 (2020): 317. http://dx.doi.org/10.15407/ujpe65.4.317.

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The optical absorption at 300 K and the fluorescence and phosphorescence at 78 K of the emissive guanine substitute, deoxythienoguanosine, (dthG) were investigated in aqueous and TRIS-HCl-buffer solutions. Two optical absorption and fluorescence centers at room temperature were attributed to two keto-enol tautomers of dthG, which confirms previously obtained results. In contrast to room temperature, only one emission band was observed at 78 K in fluorescence spectra that was close to the long-wave fluorescence band at room temperature and could be associated with the tautomer with long-wave ab

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48

Nedeltcheva-Antonova, Daniela, and Liudmil Antonov. "Ground-State Tautomerism and Excited-State Proton Transfer in 7-Hydroxy-4-methyl-8-((phenylimino)methyl)-2H-chromen-2-one as a Potential Proton Crane." Physchem 4, no. 1 (2024): 91–105. http://dx.doi.org/10.3390/physchem4010007.

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The tautomerism in the title compound as a potential long-range proton transfer (PT) switch has been studied by using the DFT and TD-DFT approaches. The data show that in aprotic solvents, the enol tautomer dominates, while the increase in the content of the keto tautomer (short-range PT) rises as a function of polarity of the solvent. In ethanol, due to specific solute–solvent stabilization through intermolecular hydrogen bonding, a substantial amount of the keto forms exists in solution. The irradiation leads to two competitive processes in the excited state, namely ESIPT and trans/cis isome

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49

Akerman, Kate J., and Orde Q. Munro. "An X-ray crystallographic and density functional theory study of (3Z)-4-(5-ethylsulfonyl-2-hydroxyanilino)pent-3-en-2-one and (3Z)-4-(5-tert-butyl-2-hydroxyanilino)pent-3-en-2-one." Acta Crystallographica Section C Crystal Structure Communications 69, no. 3 (2013): 258–62. http://dx.doi.org/10.1107/s0108270113002369.

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The Schiff base enaminones (3Z)-4-(5-ethylsulfonyl-2-hydroxyanilino)pent-3-en-2-one, C13H17NO4S, (I), and (3Z)-4-(5-tert-butyl-2-hydroxyanilino)pent-3-en-2-one, C15H21NO2, (II), were studied by X-ray crystallography and density functional theory (DFT). Although the keto tautomer of these compounds is dominant, the O=C—C=C—N bond lengths are consistent with some electron delocalization and partial enol character. Both (I) and (II) are nonplanar, with the amino–phenol group canted relative to the rest of the molecule; the twist about the N(enamine)—C(aryl) bond leads to dihedral angles of 40.5 (

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50

Peng, Chunte Sam, Bogdan I. Fedeles, Vipender Singh, et al. "Two-dimensional IR spectroscopy of the anti-HIV agent KP1212 reveals protonated and neutral tautomers that influence pH-dependent mutagenicity." Proceedings of the National Academy of Sciences 112, no. 11 (2015): 3229–34. http://dx.doi.org/10.1073/pnas.1415974112.

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Antiviral drugs designed to accelerate viral mutation rates can drive a viral population to extinction in a process called lethal mutagenesis. One such molecule is 5,6-dihydro-5-aza-2′-deoxycytidine (KP1212), a selective mutagen that induces A-to-G and G-to-A mutations in the genome of replicating HIV. The mutagenic property of KP1212 was hypothesized to originate from its amino–imino tautomerism, which would explain its ability to base pair with either G or A. To test the multiple tautomer hypothesis, we used 2D IR spectroscopy, which offers subpicosecond time resolution and structural sensit

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