FTIR – spectroscopy of intermolecular interactions of pyrrole in solutions: The influence of media and cooperativity of hydrogen bonds

Rakipov, Ilnaz T.; Petrov, Аrtem А.; Akhmadiyarov, Aydar A.; Khachatrian, Artashes A.; Klimovitskii, Alexander E.; Varfolomeev, Mikhail A.; Solomonov, Boris N.

doi:10.1016/j.molliq.2018.12.117

Cited by 10 publications

(2 citation statements)

References 47 publications

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“…We determine the rather weak molecular association using the motionally averaged signals of the free and the bound catalyst in the NMR spectra, which shift upon hydrogen-bond formation. [18][19][20] The thus obtained association constants are confirmed, using the N-H stretching vibration of the catalyst in the infrared absorption spectra, in which the bound and free catalyst can be spectrally resolved. Our results show, that CF 3 -groups indeed enhance the binding to 1,3-diphenyl-2-propenone, however, the association markedly depends on the solvent with rather weak association in toluene and dichloromethane and virtually no interaction between catalyst and substrate in acetonitrile.…”

Section: Introductionsupporting

confidence: 56%

CF3-groups critically enhance the binding of thiourea catalysts to ketones – a NMR and FT-IR study

Ehrhard

Jäger

Malm

et al. 2019

Journal of Molecular Liquids

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Substituted phenylthioureas have been established as efficient organocatalysts and substituents containing electron withdrawing CF 3 groups have been shown to enhance catalytic efficiency. The effect of the CF 3 groups on binding of catalysts to substrates in solution has however remained elusive. Here, we report on the effect of CF 3 substituted diphenylthioureas on the association with the substrate 1,3-diphenyl-2propenone in solution by using a combination of nuclear magnetic resonance (NMR) and Fourier-transform infrared (FT-IR) spectroscopy. We use the ensemble-averaged chemical shift of the thiourea proton as function of substrate concentration to determine the association constants between catalyst and substrate. To experimentally discriminate between free and bound catalyst we use infrared absorption spectra, which show a red-shift of thiourea's N-H stretching vibration upon association with the substrate. With both methods, we find the association constant K to increase from ~1 L/mol to ~20 L/mol with increasing number of CF 3 substituents. This enhanced binding can explain the increased reaction rates observed for CF 3 substituted diphenylthiourea catalysts. For the efficient catalyst containing four CF 3groups (Schreiner's catalyst), the strongest association is observed in toluene as a solvent, while the binding strength is somewhat weaker in dichloromethane, and association to the substrate is not detectable in acetonitrile. Our results thus demonstrate that even weak association between the thiourea catalysts and the ketone can facilitate efficient catalytic conversion. However, the association with the ketone substrates is very susceptible to competing interactions with the solvent.

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Section: Introductionsupporting

confidence: 56%

CF3-groups critically enhance the binding of thiourea catalysts to ketones – a NMR and FT-IR study

Ehrhard

Jäger

Malm

et al. 2019

Journal of Molecular Liquids

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“…This parameter and approach to study the contributions of intermolecular interactions of soluble substances in solvents has been successfully tested in a series of works [ 16 , 26 , 27 , 28 , 29 ]. The absorption frequencies of the C=O groups of dipeptides in solvents and the S VW parameter were compared in this work ( Figure 4 ).…”

Section: Resultsmentioning

confidence: 99%

The Solvation Effect of C=O Group of Cyclic Anhydrides in Solution

Rakipov

Akhmadiyarov

Petrov

et al. 2023

IJMS

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The paper reports the results of investigation intermolecular interactions between alanine and sarcosine anhydride in organic solvents. The absorption frequencies of cyclic dipeptide in solvents were measured by IR spectroscopy. The effect of Van der Waals interactions and the hydrogen bonding of solvents on absorption frequencies of the C=O group of anhydrides was discussed. The spectroscopic parameters for C=O∙∙∙H-O hydrogen bonding complexes of anhydride with methanol in aprotic and proton donor solvent are obtained. In multi-particle complexes of dipeptides with aliphatic alcohols, the hydrogen bond enhancement was between 10 and 16%, which is significantly lower than it is for amide complexes.

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