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Journal articles on the topic 'Tautomeric forms'

Author: Grafiati

Published: 3 June 2025

Last updated: 31 July 2025

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1

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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2

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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3

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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4

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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5

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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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

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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8

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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9

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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10

Sıdır, İsa, Yadigar Gülseven Sıdır, Halil Berber, Maria L. Ramos, Licínia L. G. Justino, and Rui Fausto. "Reversal in Solvatochromism, enol-imine/keto-amine Tautomerism and (E)-(Z) Photoisomerizations in a Benzylidene Aniline Schiff Base Derivative in Different Solvents." Molecules 30, no. 3 (2025): 745. https://doi.org/10.3390/molecules30030745.

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A novel Schiff base, (E)-4-acetyl-N-(4-hydroxy-3-methoxybenzylidene)aniline (abbreviated as ANHMA), was synthesized and characterized using infrared and 1H- and 13C-NMR spectroscopies. Optical properties in different solvents were evaluated using UV-vis absorption spectroscopy. The compound is shown to exhibit both positive and negative solvatochromism with reversal occurring for solvents with ET(30)~45 (e.g., DMSO). The solvatochromic behavior of the compound was found to be strongly dependent on the hydrogen bond abilities and polarizability of the solvent, the observed reversal in solvatoch

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11

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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12

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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13

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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14

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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15

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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16

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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17

KOSAR, BASAK. "THERMODYNAMIC AND SECOND-ORDER NON-LINEAR OPTICAL PROPERTIES OF TAUTOMERIC FORMS OF (E)-4-METHOXY-2-[(4-NITROPHENYL)IMINOMETHYL]PHENOL: A DENSITY FUNCTIONAL STUDY." Journal of Theoretical and Computational Chemistry 10, no. 03 (2011): 279–95. http://dx.doi.org/10.1142/s021963361100644x.

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This work presents a computational study on the tautomeric forms of (E)-4-Methoxy-2-[(4-nitrophenyl)iminomethyl]phenol, an ortho-hydroxy Schiff base compound. The electronic structure of title compound has been characterized at the B3LYP/6-311G(d,p) level of density functional theory. The first hyperpolarizability values have been obtained from the molecular polarizabilities for both tautomers. The second-order non-linear optical properties have been investigated based on their relationships with the natural bond orbitals and frontier molecular orbitals. The changes of thermodynamic properties

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18

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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19

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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20

Traven, Valery F., Larisa I. Vorobjeva, Tatjana A. Chibisova, Edward Andrew Carberry, and Noelle Jean Beyer. "Electronic absorption spectra and structure of hydroxycoumarin derivatives and their ionized forms." Canadian Journal of Chemistry 75, no. 4 (1997): 365–76. http://dx.doi.org/10.1139/v97-042.

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Electronic absorption spectra of 18 hydroxycoumarin derivatives and their ionized forms have been studied. Close agreement between experimental and the PPP CI calculated electron absorption band energies has been found in most cases. Strong polarization of the carbonyl function of the pyrone ring in the 7-hydroxycoumarin derivatives, H-bonding between the hydroxyl group and neighboring substituent in the ortho-substituted hydroxycoumarins, as well as their tautomeric transformations, have been suggested in the discussion of the electronic absorption spectra of the hydroxycoumarin derivatives.

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21

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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22

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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23

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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24

Rak, Janusz, Piotr Skurski, Ludwika Jozwiak, and Jerzy Blazejowski. "Theoretical Studies on the Effect of the Medium on Tautomeric Phenomena in Neutral and Protonated Acridin-9-amine. Mechanism of Tautomerization in Neutral Entities." Australian Journal of Chemistry 50, no. 2 (1997): 97. http://dx.doi.org/10.1071/c96184.

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Semiempirical AM1 and PM3 (gaseous phase) and AM1-COSMO, PM3-COSMO and PM3-AQ (liquid phase) methods were used to examine the structure, as well as the thermodynamic and physicochemical features (dipole moments and LUMO and HOMO energies), of tautomeric forms of neutral, mono- and di-protonated acridin-9-amine. The energy gaps between possible tautomers are only insignificantly influenced by the medium and reveal the coexistence of neutral and diprotonated entities in two forms, and the monoprotonated entity in one form. Entropy and thermal energy, which can be evaluated only for gaseous syste

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25

Keller, Max, Mohan M. Bhadbhade, and Roger W. Read. "Two dibenzodiazepinone molecules with dissimilar dimeric associations and apparent different tautomeric forms." Acta Crystallographica Section C Crystal Structure Communications 68, no. 6 (2012): o240—o246. http://dx.doi.org/10.1107/s0108270112019622.

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In two dibenzodiazepinones,viz.the tricyclic core structure, 5H-dibenzo[b,e]diazepin-11(10H)-one, C13H10N2O, and an acylated derivative, 1-(11-hydroxy-5H-dibenzo[b,e]diazepin-5-yl)-2-{4-[3-(1H-imidazol-1-yl)propyl]piperidin-1-yl}ethanone ethanol monosolvate, C26H29N5O2·C2H5OH, dimeric associationviahydrogen-bond bridging between the cyclic amide entities is evident, but there are considerable differences between the parent compound and the amidated derivative. Highly consistent with reported structures of related tricyclic lactams, two molecules of the nonsubstituted compound are bridged throu

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26

Raczyńska, Ewa. "Application of the Extended HOMED (Harmonic Oscillator Model of Aromaticity) Index to Simple and Tautomeric Five-Membered Heteroaromatic Cycles with C, N, O, P, and S Atoms." Symmetry 11, no. 2 (2019): 146. http://dx.doi.org/10.3390/sym11020146.

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The geometry-based HOMA (Harmonic Oscillator Model of Aromaticity) descriptor, based on the reference compounds of different delocalizations of n- and π-electrons, can be applied to molecules possessing analogous bonds, e.g., only CC, only CN, only CO, etc. For compounds with different heteroatoms and a different number of CC, CX, XX, and XY bonds, its application leads to some discrepancies. For this reason, the structural descriptor was modified and the HOMED (Harmonic Oscillator Model of Electron Delocalization) index defined. In 2010, the HOMED index was parameterized for compounds with C,

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27

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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28

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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29

Doycho, I. K., S. A. Gevelyuk, and E. Rysiakiewicz-Pasek. "PHOTOLUMINESCENCE OF TAUTOMERIC FORMS OF NANOPARTICLE ENSEMBLES OF DYES BASED ON THE 4-VALENCE STANNUM COMPLEXES IN POROUS SILICA GLASS." Photoelectronics, no. 24 (December 28, 2015): 30–37. http://dx.doi.org/10.18524/0235-2435.2015.24.158014.

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Luminescence of tautomeric forms of dyes based on the 4-valence stannum complexes was researched. Symmetry of photoluminescence spectra of different tautomeric forms relative to direction of reading of atom positions in the hydrazide fragment was found clockwise or anti clockwise. It was determined that the illumination of nanoparticle ensembles of dyes in A-type porous silica glass is always more intensive than in appropriate solution. It was shown that the luminescence intensity of tautomeric forms increases, if the substituent comes nearer to the coordination set irrespective of type and na

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30

Burdzhiev, Nikola, Anife Ahmedova, Boris Borrisov, and Robert Graf. "13C CPMAS NMR as a Tool for Full Structural Description of 2-Phenyl Substituted Imidazoles That Overcomes the Effects of Fast Tautomerization." Molecules 25, no. 17 (2020): 3770. http://dx.doi.org/10.3390/molecules25173770.

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Tautomerization of 2-phenylimidazolecarbaldehydes has not been studied in detail so far, although this process is a well-known phenomenon for imidazole derivatives. That is why we focus our study on a series of 2-phenylimidazolecarbaldehydes and their parent alcohols that were synthesized and studied by detailed 1H and 13C NMR in solution and in the solid state. The apparent problem is that the fast tautomerization impedes the full structural description of the compounds by conventional 13C NMR measurements. Indeed, the 13C NMR spectra in solution exhibit poor resolution, and in most cases, si

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31

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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Karakurt, Tuncay. "Investigation of the molecular structure of 4-(3-methyl-3-phenylcyclobutyl)-2-[2-(3-methylbenzylidene)hydrazinyl]thiazole in the gas and solid phases." Acta Crystallographica Section C Structural Chemistry 74, no. 11 (2018): 1502–8. http://dx.doi.org/10.1107/s2053229618013475.

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In this study, the title Shiff base, C22H23N3S, was synthesized and examined by 1H and 13C NMR spectroscopy and X-ray analysis techniques. The crystal structure is stabilized by classical intermolecular N—H...N hydrogen bonding. The crystal packing is additionally stabilized by C—H...π interactions. It has been observed that the compound can exist in two different tautomeric forms, and experimental and theoretical studies were carried out on these tautomeric structures. For this purpose, the gas phase of the compound was optimized by density functional theory (DFT) using the B3LYP/6-311G(d) me

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Raczyńska, Ewa Daniela. "Acid-Base Equilibria for Tautomeric Heterocycles in the Gas-Phase: A Case of Uracil." Symmetry 17, no. 2 (2025): 177. https://doi.org/10.3390/sym17020177.

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Prototropic conversion (prototropy) for heterocyclic nucleobases was already signaled by Watson and Crick about seventy years ago as one of the reasons for nucleic acids mutations. This isomeric phenomenon has been investigated for neutral derivatives by means of both experimental and theoretical procedures, and their favored tautomers discussed in numerous articles published in the last fifty years. Protonation/deprotonation reactions in the gas phase have also been studied using both quantum-chemical calculations and experimental techniques. Some thermochemical parameters of these processes

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Sharov, Artem V., Tatyana M. Burkhanova, Tugba Taskın Tok, Maria G. Babashkina, and Damir A. Safin. "Computational Analysis of Molnupiravir." International Journal of Molecular Sciences 23, no. 3 (2022): 1508. http://dx.doi.org/10.3390/ijms23031508.

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In this work, we report in-depth computational studies of three plausible tautomeric forms, generated through the migration of two acidic protons of the N4-hydroxylcytosine fragment, of molnupiravir, which is emerging as an efficient drug to treat COVID-19. The DFT calculations were performed to verify the structure of these tautomers, as well as their electronic and optical properties. Molecular docking was applied to examine the influence of the structures of the keto-oxime, keto-hydroxylamine and hydroxyl-oxime tautomers on a series of the SARS-CoV-2 proteins. These tautomers exhibited the

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Dobosz, Robert, Jan Mućko, and Ryszard Gawinecki. "Using Chou’s 5-Step Rule to Evaluate the Stability of Tautomers: Susceptibility of 2-[(Phenylimino)-methyl]-cyclohexane-1,3-diones to Tautomerization Based on the Calculated Gibbs Free Energies." Energies 13, no. 1 (2020): 183. http://dx.doi.org/10.3390/en13010183.

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Gibbs free energies, based on DFT (Density Functional Theory) calculations, prove that enaminone (2-(anilinemethylidene)cyclohexane-1,3-dione) and ketamine (2-[(phenylimino)-methyl]cyclohexane-1,3-dione) are the most and least stable tautomeric forms of the studied systems, respectively. 1H and 13C NMR spectra prove that 2-(anilinemethylidene)cyclohexane-1,3-diones are the only tautomeric species present in dimethylsulfoxide solution (a very weak signal can be seen only for the p-methoxy derivatives). The zwitterionic character of these enaminones is strengthened by naphthoannulation and by th

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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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37

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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Ou, Zhongping, Xueyan Chen, Lina Ye, et al. "N-confusedmeso-tetraaryl-substituted free-base porphyrins: determination of protonation and deprotonation constants in nonaqueous media." Journal of Porphyrins and Phthalocyanines 19, no. 01-03 (2015): 251–60. http://dx.doi.org/10.1142/s1088424614501132.

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The protonation and deprotonation reactions for a series N-confused meso-tetraaryl-substituted free-base porphyrins containing electron-donating or electron-withdrawing substituents was monitored in CHCl3and DMF by UV-visible spectroscopy during titrations with trifluoroacetic acid or tetra-n-butylammonium hydroxide. The spectroscopic data was also used to calculate equilibrium constants for these reactions. The examined compounds are represented as (XPh)4NCPH2, where "NCP" represents the N-confused porphyrin π-conjugated macrocycle and X is a CH3O , CH3, H or Cl para-substituent on the four m

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Chuchkova, N. N., K. A. Pazinenko, M. V. Smetanina, et al. "Microcirculatory Liver Bloodstream in Hyperhomocysteinemia and Administration of Tautomeric Forms of Orotic Acid." Journal of Anatomy and Histopathology 10, no. 2 (2021): 55–61. http://dx.doi.org/10.18499/2225-7357-2021-10-2-55-61.

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The aim of the study was to analyze the microvasculation of the liver in administration of tautomeric forms of orotic acid for a methionine-induced liver pathology to assess the efficacy of the modified drugs and the potentialof their clinical use.Material and methods. The study included 30 white outbred rats, that were simulated methionine induced hyperhomocysteinemia by the administration of methionine, dosage 0.15 g/100 g of the body we ight, via food during 4 weeks. Animals with hyperhomocysteinemia were divided into 4 groups: animals of group 1 received orotic acid (OA) in the initial for

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Raczyńska, Ewa Daniela. "On Some Origins of Tautomeric Preferences in Neutral Creatinine in Vacuo: Search for Analogies and Differences in Cyclic Azoles and Azines." Symmetry 16, no. 1 (2024): 98. http://dx.doi.org/10.3390/sym16010098.

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In order to look for the origins of tautomeric preferences in neutral creatinine in vacuo, we examined prototropic conversions for model azoles, namely mono-hydroxy and mono-amino imidazoles, and also for their selected 1-methyl derivatives. All possible isomeric forms of creatinine and model compounds, resulting from intramolecular proton transfer (prototropy), conformational isomerism about –OH, and configurational isomerism about =NH, were studied in the gas phase (model of non-polar environment) by means of quantum-chemical methods. Because the bond-length alternation is a consequence of t

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Vu, Anh Thi Ngoc, Mikhail A. Ryabov, Olga V. Kovalchukova, and Dmitry S. Gusarov. "Spectral and quantum chemical study of tautomeric and ion transformations of 2-(2-(2-hydroxy-5-sulfamoylphenyl)- hydrazono)-3-oxo-N-phenylbutanamide." Butlerov Communications 60, no. 11 (2019): 106–13. http://dx.doi.org/10.37952/roi-jbc-01/19-60-11-106.

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In this paper, using the method DFT/B3LYP of quantum chemical modeling, the stability of tautomeric, conformer, and anionic forms of 2-(2-(2-hydroxy-5-sulfamoylphenyl)hydrazone-3-oxo-N-phenylbutanamide (H2L) was studied and the geometric, electronic structure and bond lengths of molecules in various tautomeric forms were determined. It was shown that the stability of tautomeric molecules H2L as anionic forms was determined by the number of existing intermolecular hydrogen bonds (closing six-membered and five-membered cycles). The most stable tautomeric and conformal forms of an organic molecul

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Sbirna, Liana-Simona, and Clementina Moldovan. "Differently-charged tautomeric forms of three related hexacoordinated complex compounds of Fe(II)." Annals of the University of Craiova Series Chemistry 30, no. 1 (2024): 65–74. https://doi.org/10.52846/aucchem.2024.1.08.

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Casella, Girolamo, Maurizio Casarin, Vadim Kukushkin, and Maxim Kuznetsov. "Reaction between Indazole and Pd-Bound Isocyanides—A Theoretical Mechanistic Study." Molecules 23, no. 11 (2018): 2942. http://dx.doi.org/10.3390/molecules23112942.

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The mechanism of the addition of indazole (Ind)—a bifunctional aromatic N,NH-nucleophile—to cyclohexyl isocyanide coordinated to the palladium(II) center in the model complex cis-[PdCl2(CNMe)(CNCy)] (1) to give the corresponding aminocarbene ligand was investigated in detail by theoretical (DFT) methods. The most plausible mechanism of this reaction is that of the associative type involving nucleophilic attack of Ind by its unprotonated N atom at the isocyanide carbon atom followed by the stepwise proton transfer from the nucleophile molecule to the isocyanide N atom via deprotonation/protonat

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44

Nazarski, Ryszard B., and Małgorzata Domagała. "Unexpected Formation of 6-(1H-Benzo[d]imidazol-2-yl)-1-phenyl-hexan-1-one and Its Structure in Solution and Solid State Analyzed in the Context of Tautomerism." Crystals 14, no. 8 (2024): 704. http://dx.doi.org/10.3390/cryst14080704.

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The structure of the title compound (4d), unexpectedly obtained in the reaction between o-phenylenediamine and 2-benzoylcyclohexanone instead of the target 3H-benzo[b][1,4]diazepine derivative 3d, was determined spectroscopically in solution and by a single-crystal X-ray diffraction (XRD) study. It involves two enantiomeric rotamers, called forms D and U, of which the structure was elucidated based on NMR spectra measured and predicted in DFT-GIAO calculations. An averaging of δCs for all tautomeric positions in the benzimidazole part of the 4d hydrate studied in wet (probably slightly acidic)

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El-Gamel, Nadia E A., Lena Seyfarth, Jörg Wagler, et al. "The Tautomeric Forms of Cyameluric Acid Derivatives." Chemistry - A European Journal 13, no. 4 (2007): 1158–73. http://dx.doi.org/10.1002/chem.200600435.

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Bakalova, Sn, A. Georgieva, P. Nikolov, and E. Stanoeva. "Dihydronaphthalenone Carboxylates - Spectral Characteristics and Structure." Zeitschrift für Naturforschung A 52, no. 5 (1997): 457–61. http://dx.doi.org/10.1515/zna-1997-0514.

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Abstract The absorption and luminescence characteristics of a group of newly synthesized methyl esters of 2-alkyl (p-substituted-aryl) -aminomethylene-3,4-dihydro-1(2 H)-naphthalenone-4-carboxylic acids have been investigated. The studied compounds may exist in three tautomeric forms. On the basis of comparison of their electronic spectra to those of similar substances, the observed substituent effect on the position of the UV-VIS absorption bands, the IR spectra and the results of PPP-SCF-CI quantum-chemical calculations it is concluded that the keto tautomer predominates in solution.

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Miron, Neculai Doru, Patrice Woisel, Georgiana G. Surpateanu, Gérard Vergoten, Ludovic Depature, and Gheorghe Surpateanu. "Benzotriazolium ylides: Experimental and theoretical study on the tautomeric equilibrium of monosubstituted benzotriazolium ylides." Canadian Journal of Chemistry 81, no. 5 (2003): 350–56. http://dx.doi.org/10.1139/v03-050.

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The biphenacyl benzotriazolium salts 12 give a tautomeric equilibrium 13[Formula: see text]14 in the presence of triethylamine (TEA) or NaOH. The evaluation of this tautomeric equilibrium has been studied using a dynamic NMR analysis and a new synthetic procedure of disubstituted benzotriazolium ylides 15 and 16, which have in their structures a picryl fragment. This study also includes a theoretical analysis on the reactivity of salts 12ac and the thermodynamical stability of tautomeric forms 13 and 14 by AM1 and PM3 procedure methods.Key words: synthesis, salts, ylides, semiempirical calcul

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48

Tempczyk, A., Z. Gryczyński, A. Kawski, and Z. Grzonka. "Spectroscopic Analysis of Tautomeric Forms of 5-Phenyltetrazole." Zeitschrift für Naturforschung A 43, no. 4 (1988): 363–68. http://dx.doi.org/10.1515/zna-1988-0412.

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Abstract Experimental and theoretical directions of electronic transition moments and the UV spectra of anionic and neutral 5-phenyltetrazole (5-PhTH) have been determined. Based on the correlation between the theoretical and experimental data it has been found that the 2 H-tautomeric form is predominant in polyvinyl alcohol (PVA) film.

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Mishnev, Anatoly, and Glebs Kiselovs. "New Crystalline Forms of Piroxicam." Zeitschrift für Naturforschung B 68, no. 2 (2013): 168–74. http://dx.doi.org/10.5560/znb.2013-2268.

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Four new crystalline forms of piroxicam have been obtained and studied by single-crystal X-ray structure analysis. These comprise an addition salt with hydrochloric acid, acetic and isobutyric acids solvates, as well as piroxicam and furosemide cocrystal acetone solvate. All these new structures contribute to the variety of already known piroxicam crystalline forms. The analysis of conformations and tautomeric forms of piroxicam molecules in different crystal forms is presented.

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Wieczorkiewicz, Paweł A., Tadeusz M. Krygowski, and Halina Szatylowicz. "Intramolecular Interactions in Derivatives of Uracil Tautomers." Molecules 27, no. 21 (2022): 7240. http://dx.doi.org/10.3390/molecules27217240.

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The influence of solvents on intramolecular interactions in 5- or 6-substituted nitro and amino derivatives of six tautomeric forms of uracil was investigated. For this purpose, the density functional theory (B97-D3/aug-cc-pVDZ) calculations were performed in ten environments (1 > ε > 109) using the polarizable continuum model (PCM) of solvation. The substituents were characterized by electronic (charge of the substituent active region, cSAR) and geometric parameters. Intramolecular interactions between non-covalently bonded atoms were investigated using the theory of atoms in molecules

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