Influence of methyl and propyl groups on the vibrational spectra of two imidazolium ionic liquids and their non-ionic precursors

Boumediene Haddad, Drai Mokhtar, Mimanne Goussem, El-habib Belarbi, Didier Villemin, Serge Bresson, Mustapha Rahmouni, Nilesh R. Dhumal, Hyung J. Kim, Johannes Kiefer* (Corresponding Author)

*Corresponding author for this work

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Imidazolium-based ionic liquids (ILs) are usually synthesized using non-ionic imidazole compounds as precursors. While the ILs have been extensively studied in the past, the precursors was not paid much attention to. The structural analysis of the precursors, however, may offer an opportunity to better understand the behavior of the ionic compounds of interest. In this paper, a comparative study of two ionic liquids and their imidazole precursors is presented. The precursors 1-methylimidazole [1-MIM] and 1,2dimethylimidazole [1,2-DMIM] are compared in order to explain the influences of the methyl group at the C(2) position (methylation). Since the imidazole compounds are non-ionic, the spectroscopic properties of [1-MIM] and [1,2-DMIM] are not affected by cation-anion interactions. In addition, the products obtained by alkylation using propyl iodide leading to the corresponding IL compounds 1-methyl-3-propylimidazolium iodide [1-MPrIM+][I-] and 1,2-dimethyl-3-propylimidazolium iodide [1,2-DMPrIM+][I-] were studied. For this purpose, vibrational spectroscopy in terms of FT -Raman and FTIR in the wavenumber range from [45 to 3500 cm(-1)] and from [600 to 4000 cm(-1)], respectively, was performed. Moreover, to aid the spectral assignment, density functional theory (DFT) calculations were carried out. The aim was to investigate the vibrational structure, to understand the effects of the propyl group at the N(3) and of the methyl group at the C(2) position, and to analyze the resulting cation-anion interactions. The data indicate that the iodide ion predominantly interacts with the C(2)-H group via hydrogen bonding. Upon methylation, the C(4/5)-H moiety becomes the main interaction site. However, an interaction takes place only with one of the two hydrogen atoms resulting in a split of the initially degenerate CH stretching modes. (C) 2017 Elsevier B.V. All rights reserved.

Original languageEnglish
Pages (from-to)582-590
Number of pages9
JournalJournal of Molecular Structure
Early online date3 Jan 2017
Publication statusPublished - 15 Apr 2017


  • Ionic liquids ILs
  • Fr-Raman
  • Imidazolium
  • Methylation
  • Propylation

Cite this

Haddad, B., Mokhtar, D., Goussem, M., Belarbi, E., Villemin, D., Bresson, S., Rahmouni, M., Dhumal, N. R., Kim, H. J., & Kiefer, J. (2017). Influence of methyl and propyl groups on the vibrational spectra of two imidazolium ionic liquids and their non-ionic precursors. Journal of Molecular Structure, 1134, 582-590.