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Journal articles on the topic 'Tautomeric mixture'

Author: Grafiati

Published: 5 June 2025

Last updated: 1 August 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

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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3

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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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

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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6

Moskaeva, Elena, Ahina Mosharenkova, Sergey Shekhovtsov, and Nikolay Mchedlov-Petrossyan. "PROTOLYTIC EQUILIBRIUM OF TETRA- AND PENTANITROFLUORESCEINS IN A BINARY SOLVENT ACETONITRILE – DIMETHYL SULFOXIDE (MASS RATIO 96 : 4)." Ukrainian Chemistry Journal 87, no. 5 (2021): 25–37. http://dx.doi.org/10.33609/2708-129x.87.05.2021.25-37.

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In this paper, the acid-base and tautomeric equilibria of four nitrofluorescein dyes, 2,4,5,7-tetranitrofluorescein, 2,4,5,7,4’-pentanitrofluorescein, 2,4,5,7,5’-pentanitrofluorescein, and 2,4,5,7-tetranitrofluorescein methyl ester, were studied. As reaction media, a binary solvent acetonitrile – dimethyl sulfoxide (96 : 4 by mass) was used. The acidity scale in this solvent was established previously. The indices of the dissociation constants of the dyes were determined using the spectrophotometric method. Interpreting the values requires an understanding of the state of tautomeric eq

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7

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

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

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8

Raczyńska, E. D., M. Makowski, M. Szeląg, B. Kamińska, and K. Zientara. "Importance of CH tautomers in the tautomeric mixture of uric acid." Journal of Molecular Structure: THEOCHEM 947, no. 1-3 (2010): 83–91. http://dx.doi.org/10.1016/j.theochem.2010.01.045.

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9

Belova, L. O., N. A. Golub, M. V. Pletneva, N. I. Kirilina, and A. D. Kirilin. "Behavior of morpholine and its trimethylsilyl derivative in reactions with trimethylsilyl isocyanate." Fine Chemical Technologies 17, no. 5 (2022): 377–83. http://dx.doi.org/10.32362/2410-6593-2022-17-5-377-383.

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Objectives. To study the patterns of behavior of morpholine and its trimethylsilyl derivative in reactions with trimethylsilyl isocyanate.Methods. The study employed infrared and nuclear magnetic resonance spectroscopy, as well as elemental analysis.Results. The formation of mixtures of tautomeric forms of silicon-containing urea—N-(trimethylsilyl) morpholine-4-carboxamide and trimethylsilylmorpholine-4-carboximidoate—was established.Conclusions. It is shown that the composition and structure of the resulting products are determined both by the presence of a morpholine substituent at the nitro

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10

Wu, R. R., Bo Yang, C. E. Frieler, G. Berden, J. Oomens, and M. T. Rodgers. "Diverse mixtures of 2,4-dihydroxy tautomers and O4 protonated conformers of uridine and 2′-deoxyuridine coexist in the gas phase." Physical Chemistry Chemical Physics 17, no. 39 (2015): 25978–88. http://dx.doi.org/10.1039/c5cp02227d.

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IRMPD spectroscopy and theoretical studies reveal that a diverse mixture of minor 2,4-dihydroxy and O4 protonated tautomeric conformations of the protonated forms of uridine and 2′-deoxyuridine are populated by ESI.

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11

Devi, Lalita, Gaurav Sharma, Ruchir Kant, Sanjeev K. Shukla, and Namrata Rastogi. "Regioselective synthesis of functionalized pyrazole-chalcones via a base mediated reaction of diazo compounds with pyrylium salts." Organic & Biomolecular Chemistry 19, no. 18 (2021): 4132–36. http://dx.doi.org/10.1039/d1ob00274k.

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A base-mediated reaction of triaryl/alkyl pyrylium tetrafluoroborate salts with α-diazo-phosphonates, sulfones and trifluoromethyl compounds affords the corresponding functionalized pyrazole-chalcones as 5-P-5 and 3-P-3 tautomeric mixture.

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12

Curtis, NF, AR Davis, and FWB Einstein. "Intermediate Products of the Reaction of (4,4,9,9-Tetramethyl-5,8-diazadodecane-2,11-dione dihydrazone)nickel(II) With Butane-2,3-dione; the Structure of cis-Aqua(3,4,7,9,9,14,14,16-octamethyl-1,2,5,6,10,13-hexaazacyclohexadeca-1(16),4,6-tien-3-Ol)nickel(II) Perchlorate Trihydrate." Australian Journal of Chemistry 47, no. 10 (1994): 1885. http://dx.doi.org/10.1071/ch9941885.

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Intermediate products have been isolated from the reaction of (4,4,9,9-tetramethyl-5,8-diazadodecane-2,11-dione dihydrazone )nickel(II) perchlorate with butane-2,3-dione which finally yields the macrocyclic product (3,4,7,9,9,14,14,16-octamethyl-1,2,5,6,10,13-hexaazacyclohexa-deca-2,4,6,16-tetraene)nickel(II) perchlorate , [Ni( omht )] (ClO4)2. An initial violet product is assigned a structure with the macrocyclic ligand 3-acetyl-3,6,8,8,13,13,15-heptamethyl-1,2,4,5,9,12-hexaazacyclopentadeca-5,15-diene. In water this converts into an equilibrium mixture of the tautomeric cations blue cis-aqua

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13

Danopoulos, Andreas A., and Pierre Braunstein. "‘Janus-type’ organopotassium chemistry observed in deprotonation of mesoionic imidazolium aminides and amino N-heterocyclic carbenes: coordination and organometallic polymers." Chem. Commun. 50, no. 23 (2014): 3055–57. http://dx.doi.org/10.1039/c3cc49517e.

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Deprotonation of the observable tautomeric equilibrium mixture of mesoionic 4-aminide imidazoliums and the corresponding 4-amino NHCs allows isolation of a monomeric potassium (imidazol-2-ylidenyl)(anilide), a ‘free’ anionic carbene, or polymeric organometallics with ‘Janus-type’ anionic NHC repeat units.

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14

Danopoulos, Andreas A., Pierre Braunstein, Elixabete Rezabal, and Gilles Frison. "Unprecedented directed lateral lithiations of tertiary carbons on NHC platforms." Chemical Communications 51, no. 15 (2015): 3049–52. http://dx.doi.org/10.1039/c4cc08434a.

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Deprotonation of the tautomeric mixture of 4-amido-imidazoliums and 4-amino-N-heterocyclic carbenes led to dilithiated dianionic functional NHCs, via an unprecedented regioselective, directed remote lateral lithiation of a tertiary CHMe<sub>2</sub> carbon. DFT calculations support that the nature of products is under thermodynamic control.

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15

Yates, Peter, Azza Seif-El-Nasr, Jennifer Stanton та Jiri J. Krepinsky. "Reactions of δ-valerolactone with lithio trithio-orthoformates". Canadian Journal of Chemistry 69, № 3 (1991): 415–22. http://dx.doi.org/10.1139/v91-063.

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δ-Valerolactone (3), on treatment with tris(methylthio)methyllithium (7) followed by weakly acidic aqueous work-up, gave a tautomeric mixture of 1, 1-bis(methylthio)-6-hydroxy-2-hexanone (8a) and tetrahydro-2-bis(methylthio)methyl-2-pyranol (8b). Under analogous conditions 3 reacted with tris(phenylthio)methyllithium (10) to form tetrahydro-3-(phenylthiocarbonyl)-2-pyranone (11). With 2-(methylthio)-1,3-dithian-2-yllithium (16) it gave a tautomeric mixture of 2-(5-hydroxy-1-oxopentyl)-2-(methylthio)-1,3-dithiane (17a) and 2-(tetrahydro-2-hydroxy-2-pyranyl)-2-(methylthio)-1,3-dithiane (17b). Tr

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16

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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17

Lyčka, Antonín, Libuše Havlíčková, Alois Koloničný, and Josef Jirman. "15N NMR study of amino-imino tautomerism in derivatives of 1,4-bis(substituted amino)-9,10-anthraquinones and 1,4-bis(substituted amino)-2,3-dihydro-9,10-anthraquinones." Collection of Czechoslovak Chemical Communications 52, no. 3 (1987): 736–41. http://dx.doi.org/10.1135/cccc19870736.

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The 15N chemical shifts and 1J(15N, H) coupling constants of 1,4-bis(substituted amino)-9,10-anthraquinones and 1,4-bis(substituted amino)-2,3-dihydro-9,10-anthraquinones indicate that these derivatives exist as true aminoderivatives except for 1,4-bis(phenylamino)-2,3-dihydro-9,10-anthraquinone which forms a tautomeric mixture of the amino and imino forms in deuteriochloroform and hexadeuteriodimethyl sulphoxide.

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18

S., A. EL-ABBADY, and M. AGAMAI S. "Synthesis and Selected Reactions of 9-(2-Cyanoethyl)-1-oxa-9-azatricyclo[ 4.2.1.0 2,8]nonan-3-one-6-carbonitrile." Journal of Indian Chemical Society Vol. 73, Dec 1996 (1996): 663–65. https://doi.org/10.5281/zenodo.5918343.

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Department of Chemistry, University College for Girls, Am Shams University, Heliopolis, Cairo, Egypt <em>Manuscript received 27 January 1994, revised 16 March 1995, accepted 31 May 1995 </em> Oxirination of the activated 3,4-olefinic double bond of 8-(2-cyanoethyl)-8-azabicyclo[3.2.1]oct-3-en-2-one-6-carbonitrile (1) with basic hydrogen peroxide afforded 9-(2-cyanoethyl)-1-oxa-9-azatricyclo[4.2.1.0<sup>2,8</sup>]nonan-3-one-6-carbonitrile (2). Ring opening of the oxirane ring in 2 has been investigated using 10% sodium hydroxide, acetic acid and phenylhydrazine to give 4, 7 and 8 respecti

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19

Raczyńska, Ewa D. "Quantum-Chemical Search for Keto Tautomers of Azulenols in Vacuo and Aqueous Solution." Symmetry 13, no. 3 (2021): 497. http://dx.doi.org/10.3390/sym13030497.

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Keto-enol prototropic conversions for carbonyl compounds and phenols have been extensively studied, and many interesting review articles and even books appeared in the last 50 years. Quite a different situation takes place for derivatives of biologically active azulene, for which only scanty information on this phenomenon can be found in the literature. In this work, quantum-chemical studies have been undertaken for symmetrically and unsymmetrically substituted azulenols (constitutional isomers of naphthols). Stabilities of two enol (OH) rotamers and all possible keto (CH) tautomers have been

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20

Shahi, Neelam, Kumar Shah, Prasad Yadav, and Ajaya Bhattarai. "The spectral study of azo dye and cationic surfactant interaction in ethanol-water mixture." Journal of the Serbian Chemical Society 86, no. 5 (2021): 483–94. http://dx.doi.org/10.2298/jsc201116020s.

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The interaction of the azo dye methyl red (MR) with dodecyl trimethyl ammonium bromide (DTAB) has been studied by the spectrometric methods through the azo-hydrazone tautomeric behaviour of MR for a series of the ethanol?water system (0.1, 0.2, 0.3 and 0.4 volume fractions of ethanol) at room temperature. The critical micelle concentration was determined using the conductometric technique with the increased ethanol volume, influenced by the solvent polarity and the architectural flexibility of methyl red. The azo form of methyl red brings the electrostatic interaction with the cationic surfact

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21

Klarek, Mateusz, Tomasz Siodła, Tahar Ayad, David Virieux та Magdalena Rapp. "Access to 2-Fluorinated Aziridine-2-phosphonates from α,α-Halofluorinated β-Iminophosphonates—Spectroscopic and Theoretical Studies". Molecules 28, № 14 (2023): 5579. http://dx.doi.org/10.3390/molecules28145579.

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The efficient one-pot halofluorination of a β-enaminophosphonate/β-iminophosphonate tautomeric mixture resulting in α,α-halofluorinated β-iminophosphonates is reported. Subsequent imine reduction gave the corresponding β-aminophosphonates as a racemic mixture or with high diastereoselectivity. The proposed protocol is the first example of a synthesis of N-inactivated aziridines substituted by a fluorine and phosphonate moiety on the same carbon atom. Based on spectroscopic and theoretical studies, we determined the cis/trans geometry of the resulting fluorinated aziridine-2-phosphonate. Our pr

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22

PAUL, R. Gordon, C. Nicholas AVERY, A. David SLATTER, J. Trevor SIMS, and J. Allen BAILEY. "Isolation and characterization of advanced glycation end products derived from the in vitro reaction of ribose and collagen." Biochemical Journal 330, no. 3 (1998): 1241–48. http://dx.doi.org/10.1042/bj3301241.

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An amino acid component, NFC-1, when formed in vitro by the reaction of ribose and protein was shown to comprise a complex mixture of high and low molecular AGE compounds. Two low-molecular-weight components have been successfully isolated and their structure determined. These were αNFC-1 [NΔ-(4-oxo-5-dihydroimidazol-2-yl)-l-ornithine] and βNFC-1 a 4-imidazolon-2-yl derivative existing in three tautomeric forms. These imidazolone compounds have been shown to originate from the reaction of arginine with glyoxal and methylglyoxal, respectively. A third ninhydrin-positive AGE, γNFC-1, was shown t

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23

Belaya, Natal'ya I., Aleksandr V. Belyi, Galina A. Tikhonova, Yaroslav S. Udalov, and Galina O. Andriyenko. "SYNERGISTIC EFFECT OF BINARY QUERCETIN–MONOSACCHARIDE MIXTURES IN THE RE-ACTION WITH FREE RADICALS." IZVESTIYA VYSSHIKH UCHEBNYKH ZAVEDENII KHIMIYA KHIMICHESKAYA TEKHNOLOGIYA 62, no. 2 (2019): 38–42. http://dx.doi.org/10.6060/ivkkt.20196202.5822.

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The presence of a synergistic effect of binary mixtures of quercetin–monosaccharide in the model reaction with the 2,2'-diphenyl-1-picrylhydrazyl radical in deoxygenated ethanol was established. It was shown that the studied carbohydrates related to the tetrose, pentose and hexose groups exhibit a synergistic effect to some extent enhancing the anti-radical effect of quercetin. The synergistic effect of the mixture is determined by the number of hydroxyl substituents and by the presence of aldehyde or ketone groups in carbohydrate molecules. The synergistic compositions of quercetin with gluco

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24

Masternak, Anna, Bogdan Skalski, and Jan Milecki. "NMR spectra of the tautomeric mixture of two forms of 6-azidopurine ribonucleoside labeled with15N." Journal of Labelled Compounds and Radiopharmaceuticals 50, no. 1 (2007): 43–46. http://dx.doi.org/10.1002/jlcr.1155.

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25

Saito, Katsuhiro, Tetsuya Watanabe, and Kensuke Takahashi. "[4+2]-Type Cycloadditions of Tropone and Heptafulvene Derivatives with a Tautomeric Mixture of Cycloheptatrienylidene and Cycloheptatetraene." Chemistry Letters 18, no. 12 (1989): 2099–102. http://dx.doi.org/10.1246/cl.1989.2099.

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26

Truong, Ngoc Hung, Thi Hong Ha Tran, Kim Chi Hoang, et al. "Novel Thioethers of Dihydroartemisinin Exhibiting Their Biological Activities." Heteroatom Chemistry 2023 (February 9, 2023): 1–10. http://dx.doi.org/10.1155/2023/6761186.

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Eleven conjugates between dihydroartemisinin (DHA) with thiols containing both ether and thioether bonds were designed, synthesized by a two-step procedure including etherification and S-alkylation. Analysis of the NMR spectral data indicated that the dimer of DHA with thiols 6-mercaptopurine and 2-mercaptoimidazole was produced with yields of 31% and 62%, respectively. Furthermore, the tautomerization of thiol 5-methoxy-2-mercaptobenzimidazole led to the formation of a mixture of two isomers in which they might be interchangeable through a dynamic tautomeric equilibrium in the solution. Scree

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27

Gdaniec, Maria, Franciszek Sączewski та Tomasz Dębowski. "α-Iminohydroxylamine-α-aminonitrone tautomerism: a 1∶1 mixture of two tautomeric forms in crystals of N-(4,5-dihydro-1H-imidazol-2-yl)-N-phenyl-hydroxylamine". Journal of Chemical Crystallography 25, № 12 (1995): 813–21. http://dx.doi.org/10.1007/bf01671076.

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28

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

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

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29

Ghogomu, Julius Numbonui, and Nyiang Kennet Nkungli. "A DFT Study of Some Structural and Spectral Properties of 4-Methoxyacetophenone Thiosemicarbazone and Its Complexes with Some Transition Metal Chlorides: Potent Antimicrobial Agents." Advances in Chemistry 2016 (November 21, 2016): 1–15. http://dx.doi.org/10.1155/2016/9683630.

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Recent studies have shown that 4-methoxyacetophenone thiosemicarbazone (MAPTSC) and its complexes with some transition metal chlorides are potent antimicrobial agents. To deepen the understanding of their structure-activity relationships necessary for rational drug design, their structural and spectral properties, along with thione-thiol tautomerism of MAPTSC, have been studied herein using the density functional theory (DFT). From our results, the thione tautomer of MAPTSC is more stable than the thiol counterpart in ethanolic solution, and thione-to-thiol tautomerization is highly precluded

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30

Paez, M., I. Martínez-Castro, J. Sanz, A. Olano, A. Garcia-Raso, and F. Saura-Calixto. "Identification of the components of aldoses in a tautomeric equilibrium mixture as their trimethylsilyl ethers by capillary gas chromatography." Chromatographia 23, no. 1 (1987): 43–46. http://dx.doi.org/10.1007/bf02310417.

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31

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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32

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

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

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33

Abraham, Raymond J., M. Ashley Cooper, Amin Aghamohammadi, Kamyar Afarinkia, and Xiangli Liu. "The Use of MM/QM Calculations of 13C Chemical Shifts in the Analysis of Edaravone Tautomers." Journal of Solution Chemistry 51, no. 9 (2022): 1162–67. http://dx.doi.org/10.1007/s10953-022-01186-8.

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AbstractThe 13C NMR chemical shifts of the three Edaravone tautomers (keto, enol, and amine) were calculated using a combined molecular mechanics (Pcmod 9.1/MMFF94) and ab initio (GIAO (B3LYP/DFT, 6–31 + G(d)) model. This method gave such good agreement with experiment that the assignment of the complex spectrum of Edaravone in solution, which is a mixture of the three tautomers could be made. This has been attempted previously by various methods with diverse results. In CDCl3 solution, the observed spectra show only one form, the keto tautomer, and this is also the case with acetonitrile solv

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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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Szarek, Walter A., Robert J. Rafka, Te-Fang Yang, and Olivier R. Martin. "Structure–sweetness relationships for fructose analogs. Part III. 3-Deoxy-D-erythro-hexulose (3-deoxy-D-fructose): composition in solution and evaluation of sweetness." Canadian Journal of Chemistry 73, no. 10 (1995): 1639–44. http://dx.doi.org/10.1139/v95-203.

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As part of continuing studies on the structural features responsible for the intense sweetness of D-fructose, 3-deoxy-D-erythro-hexulose (3-deoxy-D-fructose, 1) was prepared, its solution composition was determined, and its taste was evaluated. In aqueous solution, 3-deoxy-D-fructose exists as a complex mixture of five tautomeric forms in which the β-D-pyranose form is preponderant (52.5% at 22 °C) and the α-D-pyranose form is the least abundant (5%). Quite remarkable is the behavior of the open-chain keto form of 1: its content increases from 7.5% at 22 °C, to 36% at 82 °C, and to 47% at 97 °

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36

Henyecz, Réka, Bianka Huszár, Viktória Grenitzer, and György Keglevich. "A Study on the Reactivity of Monosubstituted Benzenes in the MW-Assisted Pd(OAc)2-catalyzed Hirao Reaction with Ph2P(O)H and (EtO)2P(O)H Reagents." Current Organic Chemistry 24, no. 9 (2020): 1048–54. http://dx.doi.org/10.2174/1385272824999200403170827.

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The reactivity order of “iodobenzene > bromobenzene > phenyl trifluoromethanesulfonate” was established in microwave (MW)-assisted Pd(OAc)2-catalyzed P–C coupling reactions with diphenylphosphine oxide and diethyl phosphite, where the excess of the these >P(O)H reagents served as the reducing agent, and, via its tautomeric >P-OH form, also as the P-ligand. The P–C coupling of Ph2P(O)H with PhBr at 120 °C took place via an induction period, during which the active “P-Pd-P” catalyst was formed from the Pd(II) salt and the >P(O)H species. The lower reactivity of PhBr towards Ph2P(O

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Dobrikov, Georgi M., Yana Nikolova, Ivaylo Slavchev, et al. "Structure and Conformational Mobility of OLED-Relevant 1,3,5-Triazine Derivatives." Molecules 28, no. 3 (2023): 1248. http://dx.doi.org/10.3390/molecules28031248.

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A series of OLED-relevant compounds, consisting of 1,3,5-triazine core linked to various aromatic arms by amino group, has been synthesized and characterized. The studied compounds exist in solution as a mixture of two conformers, a symmetric propeller and asymmetric conformer, in which one of the aromatic arms is rotated around the C-N bond. At temperatures below −40 °C, the VT NMR spectra in DMF-d7 are in a slow exchange regime, and the signals of two conformers can be elucidated. At temperatures above 100 °C, the VT NMR spectra in DMSO-d6 are in a fast exchange regime, and the averaged spec

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Ahmed, Mohamed Ali, Maksim A. Zhernakov, Edward M. Gilyazetdinov, et al. "Complexes of NiII, CoII, ZnII, and CuII with Promising Anti-Tuberculosis Drug: Solid-State Structures and DFT Calculations." Inorganics 11, no. 4 (2023): 167. http://dx.doi.org/10.3390/inorganics11040167.

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Four new NiII, CoII, ZnII, and CuII complexes with the promising anti-tuberculosis drug (E/Z)-N′-((5-Hydroxy-3,4-bis(hydroxymethyl)-6-methylpyridin-2-yl)methylene)-isonicotino-hydrazide (LH) were synthesized and characterized by structural methods: single-crystal X-ray diffraction, vibrational spectroscopy, and mass spectrometry. The NiII, CoII, and ZnII metal ions form only amorphous phases with various morphologies according to mass spectrometry and IR spectroscopy. The CuII forms a crystalline 1D coordination polymer with the relative formula {[CuLCl]·0.5H2O}∞1. Even though the LH ligand in

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Grabelnykh, V. A., I. N. Bogdanova, N. G. Sosnovskaya, et al. "Characteristics of 2-chloropyridine and thiourea condensation. Structure of the as-formed products and their effect on coating properties during electrochemical nickel plating." Proceedings of Universities. Applied Chemistry and Biotechnology 12, no. 4 (2023): 498–505. http://dx.doi.org/10.21285/2227-2925-2022-12-4-498-505.

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The synthesis and spectral characterisation of 2-pyridylisothiuronium chloride were performed by regulating the rate of feeding 2-chloropyridine into a thiourea solution in ethyl alcohol for ensuring its low concentration in the reaction zone. According to the data of NMR spectroscopy (1H,13С,15N), the obtained compound represents an approximately equimolar mixture of two tautomers: the expected isothiuronium salt and pyridinium chloride with an isothiocarbamide substituting group in the 2nd position. The ability of isothiuronium salt to transit tautomerically to pyridinium salt is determined

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Martin, Osvaldo A., Yury Vorobjev, Harold A. Scheraga, and Jorge A. Vila. "Outline of an experimental design aimed to detect protein A mirror image in solution." PeerJ Physical Chemistry 1 (October 15, 2019): e2. http://dx.doi.org/10.7717/peerj-pchem.2.

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There is abundant theoretical evidence indicating that a mirror image of Protein A may occur during the protein folding process. However, as to whether such mirror image exists in solution is an unsolved issue. Here we provide outline of an experimental design aimed to detect the mirror image of Protein A in solution. The proposal is based on computational simulations indicating that the use of a mutant of protein A, namely Q10H, could be used to detect the mirror image conformation in solution. Our results indicate that the native conformation of the protein A should have a pKa, for the Q10H

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Kubicki, Maciej. "Two tautomers in one crystal: 4(5)-nitro-5(4)-methoxyimidazole." Acta Crystallographica Section B Structural Science 60, no. 2 (2004): 191–96. http://dx.doi.org/10.1107/s0108768104003179.

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The case of prototropic annular tautomerism in an imidazole derivative has been found. The crystal structure contains a 50:50 mixture of two tautomers: 4-nitro-5-methoxyimidazole and 5-nitro-4-methoxyimidazole. The X-ray experiment actually shows the superposition of these compounds; it appears as if the structure is centrosymmetric and the N—H hydrogen atoms are disordered over two ring N atoms. Owing to the hydrogen-bond pattern, the values of their site occupation factors have to be exactly equal to 1/2. The molecules are connected into a three-dimensional network by means of N—H...N and C—

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Cysewski, Piotr, Tomasz Jeliński, and Maciej Przybyłek. "Intermolecular Interactions of Edaravone in Aqueous Solutions of Ethaline and Glyceline Inferred from Experiments and Quantum Chemistry Computations." Molecules 28, no. 2 (2023): 629. http://dx.doi.org/10.3390/molecules28020629.

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Edaravone, acting as a cerebral protective agent, is administered to treat acute brain infarction. Its poor solubility is addressed here by means of optimizing the composition of the aqueous choline chloride (ChCl)-based eutectic solvents prepared with ethylene glycol (EG) or glycerol (GL) in the three different designed solvents compositions. The slurry method was used for spectroscopic solubility determination in temperatures between 298.15 K and 313.15 K. Measurements confirmed that ethaline (ETA = ChCl:EG = 1:2) and glyceline (GLE = ChCl:GL = 1:2) are very effective solvents for edaravone.

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43

Schwade, Vânia Denise, and Bárbara Tirloni. "One- and two-dimensional PbII compounds resulting from reaction of PbBr2 and Pb(SCN)2 with pyrimidine-2-thione." Acta Crystallographica Section C Structural Chemistry 77, no. 7 (2021): 402–10. http://dx.doi.org/10.1107/s2053229621006379.

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Pyrimidine-2-thione (HSpym) reacts with lead(II) thiocyanate and lead(II) bromide in N,N-dimethylformamide (DMF) to form poly[(μ-isothiocyanato-κ2 N:S)(μ4-pyrimidine-2-thiolato-κ6 N 1,S:S:S:S,N 3)lead(II)], [Pb(C4H3N2S)(NCS)] n or [Pb(Spym)(NCS)] n , (I), and the polymeric one-dimensional (1D) compound catena-poly[[μ4-bromido-di-μ-bromido-(μ-pyrimidine-2-thiolato-κ3 N 1,S:S)(μ-pyrimidine-2-thione-κ3 N 1,S:S)dilead(II)] N,N-dimethylformamide monosolvate], {[Pb2Br3(C4H3N2S)(C4H4N2S)]·C3H7NO} n or {[Pb2Br3(Spym)(HSpym)]·DMF} n , (IIa), respectively. Poly[μ4-bromido-di-μ3-bromido-(μ-pyrimidine-2-t

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44

Hallé, Jean-Claude, Jacques Lelievre, and François Terrier. "Solvent effect on preferred protonation sites in nicotinate and isonicotinate anions." Canadian Journal of Chemistry 74, no. 4 (1996): 613–20. http://dx.doi.org/10.1139/v96-065.

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Potentiometric determinations of the two successive acidities of nicotinic and isonicotinic acids (AH2+) have been carried out in aqueous dimethyl sulfoxide mixtures containing up to 95% Me2SO by volume. In both systems, the results reveal that the addition of Me2SO induces a proton transfer from the pyridinium ring to the carboxylate group, the tautomeric equilibrium between the neutral forms of the two acids being displaced toward the zwitterionic form (AH±) in aqueous solution, but toward the molecular form (AH°) in Me2SO. An analysis of the data by means of Hammett relationships previously

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Nishimura, N., K. Danjo, Y. Sueishi, and S. Yamamoto. "Solvent and Pressure Effects on the Tautomeric Equilibrium of 4-Phenylazo-1-naphthol." Australian Journal of Chemistry 41, no. 6 (1988): 863. http://dx.doi.org/10.1071/ch9880863.

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The azo-hydrazone tautomerism of 4-phenylazo-1-naphthol has been studied in ethanol-water and acetone-water systems and at high pressures. The hydrazone form is favoured by adding water to organic cosolvents and by applying pressure. The effects of solvent polarity and pressure on the equilibrium constant (KT) between the tautomers were examined by using Kirkwood-type equations applied to chemical equilibrium. Remarkable deviations were observed in the Kirkwood plots for both types of mixtures. Solvent-induced polarization, especially of the hydrazone form in a high polarity region, was sugges

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46

Chivers, Tristram, Katherine McGregor, Masood Parvez, Ignacio Vargas-Baca, and Tom Ziegier. "Molecular and electronic structures of the purple chromophore RC(NH2)(NSePh) (R = H, 4-CH3C6H4)." Canadian Journal of Chemistry 73, no. 8 (1995): 1380–85. http://dx.doi.org/10.1139/v95-170.

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The reaction of Li[4-CH3C6H4C(NSiMe3)2] with PhECl (E = S, Se) in a 1:1 molar ratio produces the monosubstituted derivatives 4-CH3C6H4C(NEPh)[N(SiMe3)2] (3b, E = Se; 3d, E = S). The thermolysis of 3b at 130 °C produces PhSeN(SiMe3)2 and 4-CH3C6H4CN. Crystals of 3b slowly acquire a purple stain upon prolonged standing at 23 °C owing to the formation of 4-CH3C6H4C(NH2)(NSePh) (4c, λmax = 551 nm). The formamidine derivative HC(NH2)(NSePh) (4a, λmax = 472 nm) was isolated from the reaction of HCN2(SiMe3)3 with PhSeCl (1:3 molar ratio) in dichloromethane. The structure of 4a was shown by X-ray crys

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Rajam, Ammaiyappan, P. Thomas Muthiah, Ray J. Butcher, Jerry P. Jasinski, and Christopher Glidewell. "Cation tautomerism, twinning and disorder in the triclinic and monoclinic forms of 4-amino-5-chloro-2,6-dimethylpyrimidinium 5-chloro-2-hydroxybenzoate and a new disordered refinement of 2-amino-4,6-dimethoxypyrimidin-1-ium thiophene-2-carboxylate." Acta Crystallographica Section C Structural Chemistry 73, no. 11 (2017): 862–68. http://dx.doi.org/10.1107/s2053229617013481.

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Pyrimidines are important compounds in biology and medicine, and the aminopyrimidine fragment can be identified in three of the four bases in DNA. The targeted drug action of pharmaceuticals containing this functionality is likely to depend heavily on molecular recognition processes involving hydrogen bonding. Crystallization of an equimolar mixture of 4-amino-5-chloro-2,6-dimethylpyrimidine and 5-chloro-2-hydroxybenzoic acid yielded two forms of the 1:1 salt, C6H9ClN3 +·C7H4ClO3 −, each containing a different tautomeric form of the cation. 6-Amino-5-chloro-2,4-dimethylpyrimidin-1-ium 5-chloro

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Pinaki, Saha, Samanta Debasish, and Ghosh Prasanta. "A ruthenium(II) complex of glyoxalbis(2-methoxyanil) (gmha) and the redox series : Radical non-radical states." Journal of Indian Chemical Society Vol. 92, Dec 2015 (2015): 1885–92. https://doi.org/10.5281/zenodo.5599884.

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Department of Chemistry, R. K. Mission Residential College, Narendrapur, Kolkata-700 103, India <em>E-mail</em> : ghosh@pghosh.in Fax : 91-33-24773597 The article reports on a glyoxalbis(2-methoxyanil) (gmha) complex of ruthenium(II) of type <em>cis</em>- [Ru<sup>II</sup>(gmha)(PPh<sub>3</sub> )Cl<sub>2</sub> ] (1). Single crystal X-ray bond parameters of the diimine fragment of 1 are severely deformed due to mixing of d<sub>Ru</sub> and 𝝅* orbitals : 1, C=N, 1.308(3), C-C, 1.404(4) Å. The redox activity of 1 is solvent dependent. In CH<sub>2</sub>Cl<sub>2</sub> , the anodic wave due to

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49

Perrin, Charles L. "Symmetry of Hydrogen Bonds: Application of NMR Method of Isotopic Perturbation and Relevance of Solvatomers." Molecules 28, no. 11 (2023): 4462. http://dx.doi.org/10.3390/molecules28114462.

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Short, strong, symmetric, low-barrier hydrogen bonds (H-bonds) are thought to be of special significance. We have been searching for symmetric H-bonds by using the NMR technique of isotopic perturbation. Various dicarboxylate monoanions, aldehyde enols, diamines, enamines, acid–base complexes, and two sterically encumbered enols have been investigated. Among all of these, we have found only one example of a symmetric H-bond, in nitromalonamide enol, and all of the others are equilibrating mixtures of tautomers. The nearly universal lack of symmetry is attributed to the presence of these H-bond

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Solaris, Janak, Taylor D. Krueger, Cheng Chen, and Chong Fang. "Photogrammetry of Ultrafast Excited-State Intramolecular Proton Transfer Pathways in the Fungal Pigment Draconin Red." Molecules 28, no. 8 (2023): 3506. http://dx.doi.org/10.3390/molecules28083506.

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Proton transfer processes of organic molecules are key to charge transport and photoprotection in biological systems. Among them, excited-state intramolecular proton transfer (ESIPT) reactions are characterized by quick and efficient charge transfer within a molecule, resulting in ultrafast proton motions. The ESIPT-facilitated interconversion between two tautomers (PS and PA) comprising the tree fungal pigment Draconin Red in solution was investigated using a combination of targeted femtosecond transient absorption (fs-TA) and excited-state femtosecond stimulated Raman spectroscopy (ES-FSRS)

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