The structure of azines derived from <i>C</i>‐formyl‐1<i>H</i>‐imidazoles in solution and in the solid state: tautomerism, configurational and conformational studies

Pinto, José Cardoso; Silva, Vera L. M.; Silva, Artur M. S.; Claramunt, Rosa M.; Sanz, Dionísia; Torralba, M. Carmen; Torres, M. Rosario; Reviriego, Felipe; Alkorta, Ibón; Elguero, José

doi:10.1002/mrc.3926

Cited by 18 publications

(6 citation statements)

References 71 publications

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“…Actually, this was a very common occurrence, but in the series of compounds of Table 1, only for benzimidazole itself and for 3 , average signals were observed in DMSO- d 6 , a solvent known to slow down the prototropic exchanges. For these two compounds, we recorded the spectra in HMPA- d 18 , which is better for this purpose [25] observing the signals of compounds where the prototropic exchange is blocked.…”

Section: Resultsmentioning

confidence: 99%

An experimental and theoretical NMR study of NH-benzimidazoles in solution and in the solid state: proton transfer and tautomerism

Nieto¹,

Cabildo²,

García³

et al. 2014

Beilstein J. Org. Chem.

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

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Section: Resultsmentioning

confidence: 99%

An experimental and theoretical NMR study of NH-benzimidazoles in solution and in the solid state: proton transfer and tautomerism

Nieto¹,

Cabildo²,

García³

et al. 2014

Beilstein J. Org. Chem.

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“…These equations were established using a large collection of data and relate the calculated values for the gas phase with experimental values determined in solution and in the solid state [only () and ()] . For this reason, GIAO calculations over PCM solvated molecules do not improve considerably the results.…”

Section: Methodsmentioning

confidence: 99%

The structures of two aldazines: [1,1′‐(1E,1′E)‐hydrazine‐1,2‐diylidenebis(methan‐1‐yl‐1‐ylidene)dinaphthalen‐2‐ol] (Lumogen) and 2,2′‐(1E,1′E)‐hydrazine‐1,2‐diylidenebis(methan‐1‐yl‐1‐ylidene)diphenol (salicylaldazine) in the solid state and in solution

Silva

Claramunt

et al. 2013

Magnetic Reson in Chemistry

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A combination of NMR spectroscopy and theoretical methods Density functional theory including dispersion corrections (DFT‐D) was used to study the structures of Lumogen and salicylaldazine. In the solid state, Lumogen exists as the dihydroxy tautomer 1a (an azine, CN–NC) as was already known from an X‐ray determination. In a deuterated dimethyl sulfoxide solution, another tautomer is observed besides 1a; its structure corresponds to the hydroxy‐oxo tautomer 1b (a hydrazone, CN–NH–Csp2). In what concerns salicylaldazine, we have observed only the dihydroxy tautomer 2a. Copyright © 2013 John Wiley & Sons, Ltd.

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“…This approach, however, is limited by phase transitions of the used solvent and the thermal stability of the analyzed compounds. Solid-state NMR spectroscopy, in particular 13 C CP-MAS (cross-polarization magic angle spinning) NMR methods, has been successfully used for complete structural description of various tautomeric compounds [ 20 , 21 , 22 , 23 ] and even for their metal complexes [ 24 , 25 , 26 ]. In most cases, the experimental data are correlated with theoretical calculations, usually taking into account both the molecular forms and the media effects on tautomerism—either as a polarity or discrete intermolecular interactions [ 27 ].…”

Section: Introductionmentioning

confidence: 99%

13C CPMAS NMR as a Tool for Full Structural Description of 2-Phenyl Substituted Imidazoles That Overcomes the Effects of Fast Tautomerization

et al. 2020

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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, signals from the imidazole ring are not detectable. To avoid this problem, we used 13C CP-MAS NMR as an alternative spectroscopic method for unambiguous spectroscopic characterization of the studied series of 2-phenylimidazoles. The data were analyzed in combination with quantum chemical DFT-GIAO methods by considering the tautomerization process and the intermolecular interactions. The DFT (B3LYP/6-31G(d,p)) calculations allowed to identify and suggest the preferred tautomer in the gas phase and in DMSO solvent, which for alcohols are (2-phenyl-1H-imidazol-4-yl)methanol and its analogs, and for the aldehydes are the 2-phenyl-1H-imidazole-5-carbaldehydes. The gas-phase calculated energy differences between the two possible tautomeric forms are in the range 0.645–1.415 kcal/mol for the alcohols and 2.510–3.059 kcal/mol for the aldehydes. In the DMSO solvent, however, for all compounds, the calculated energy differences go below 1.20 kcal/mol. These data suggest that both tautomeric forms of the studied 2-phenylimidazoles can be present in solution at room temperature. Our data from detailed 2D NMR measurements in the solid state (1H-13C HETCOR and 1H-1H double-quantum coherence MAS NMR) suggested that also in the solid state both tautomers coexist in different crystalline domains. This fact does not obscure the 13C CP-MAS NMR spectra of the studied 2-phenyl substituted imidazoles and suggests this spectroscopic method as a powerful tool for a complete structural description of tautomeric systems with aromatic conjugation.

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The structure of azines derived from C‐formyl‐1H‐imidazoles in solution and in the solid state: tautomerism, configurational and conformational studies

Cited by 18 publications

References 71 publications

An experimental and theoretical NMR study of NH-benzimidazoles in solution and in the solid state: proton transfer and tautomerism

An experimental and theoretical NMR study of NH-benzimidazoles in solution and in the solid state: proton transfer and tautomerism

The structures of two aldazines: [1,1′‐(1E,1′E)‐hydrazine‐1,2‐diylidenebis(methan‐1‐yl‐1‐ylidene)dinaphthalen‐2‐ol] (Lumogen) and 2,2′‐(1E,1′E)‐hydrazine‐1,2‐diylidenebis(methan‐1‐yl‐1‐ylidene)diphenol (salicylaldazine) in the solid state and in solution

13C CPMAS NMR as a Tool for Full Structural Description of 2-Phenyl Substituted Imidazoles That Overcomes the Effects of Fast Tautomerization

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