NMR Parameters of Imidazolium Ionic Liquids as Indicators of Their State and Properties in Aqueous Solutions
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NMR Parameters of Imidazolium Ionic Liquids as Indicators of Their State and Properties in Aqueous Solutions A. A. Shahkhatuni1 · A. G. Shahkhatuni1 · S. S. Mamyan1 · V. P. Ananikov2 · A. S. Harutyunyan1 Received: 18 March 2020 / Accepted: 29 August 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Seven 1-methylimidazolium-based ionic liquids (ILs) and their aqueous solutions were systematically investigated in order to explore how the NMR spectroscopic properties (chemical shifts, spin–spin coupling constants) are connected or correlated with several physical and chemical properties (density, viscosity, water content, etc.) of ILs and their aqueous mixtures. 1H and 13C NMR chemical shifts of ILs vary markedly depending on different anions, alkyl chain length, and water content. Addition of water affected the NMR parameters in various manners, altering several of them significantly, while others did not change distinctly. Dissimilar behavior of NMR parameters in various solvents at various concentrations allows one to conclude that they reflect several contributions from different properties of ILs and can be used for deep structural investigations. Keywords Ionic liquids · NMR spectroscopy · Chemical shifts · Spin–spin coupling constants · Aqueous mixtures
1 Introduction Ionic liquids (ILs) are a relatively novel class of compounds widely used as solvents in modern chemistry and chemical technology [1–4] due to a number of their attractive properties: thermal and chemical stability, low melting point, wide temperature range of the liquid state, low vapor pressure, incombustibility, good electrical conductivity, etc. The rapidly growing scope of IL applications requires the development of reliable and easily measured physicochemical parameters that efficiently describe (and possibly predict) the state and properties of a given medium. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s1095 3-020-01044-5) contains supplementary material, which is available to authorized users. * A. A. Shahkhatuni [email protected] 1
Molecule Structure Research Center, Scientific Technological Center of Organic and Pharmaceutical Chemistry, National Academy of Sciences, Yerevan, Armenia
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N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow, Russia
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Vol.:(0123456789)
Journal of Solution Chemistry
Therefore the search for molecular indicators of the state of IL with the aim to govern the physicochemical processes in the ILs is an important fundamental task. Reliable measurable parameters connected both with molecules of the IL itself and with the molecules of other compounds (probes) can be used as plausible indicators. Ionic liquids and their solutions are very complex, multicomponent, structured, heterophasic systems with branched hydrogen bonding networks. Due to structural features and practical applications of ILs, determined by this complexity [4–8], the properties characterizing ILs as solvents (d
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