Raman spectra of acetonitrile in imidazolium ionic liquids

• Published in: Journal of Raman spectroscopy 2010-12, Vol.41 (12), p.1720-1724
• Main Authors: Garcia, Humberto C., de Oliveira, Luiz F. C., Nicolau, Bruno G., Ribeiro, Mauro C. C.
• Format: Article
• Language: English
• Subjects: Acetonitrile; Anions; Cations; Dielectric constant; Ionic liquids; Polarity; Raman spectra; Stretching
• ISSN: 0377-0486; 1097-4555; 1097-4555
• DOI: 10.1002/jrs.2628

Raman spectra of dilute solutions of acetonitrile in ionic liquids reveal the characteristic features of ionic liquids' polarity. This is accomplished by investigating the Raman bandshape of the ν (CN) band, corresponding to the CN stretching mode of CH3CN, which is a very sensitive probe of the local environment. The amphiphilic nature of the CH3CN molecule allows us to observe the effect of electron pair acceptor and electron pair donor characteristics on ionic liquids. It has been found that the overall polarity of nine different ionic liquids based on 1‐alkyl‐3‐methylimidazolium cations is more dependent on the anion than cation. The observed wavenumber shift of the ν (CN) band of CH3CN in ionic liquids containing alkylsulfate anions agrees with the significant different values previously measured for the dielectric constant of these ionic liquids. The conclusions obtained from the analysis of the ν (CN) band were corroborated by the analysis of the symmetric ν1 (CD3 ) stretching mode of deuterated acetonitrile in different ionic liquids. Copyright © 2010 John Wiley & Sons, Ltd. Raman bandshapes of the CN stretching mode of CH3CN, ν(CN) and the symmetric ν1 CD3 stretching mode of CD3CN, reveal characteristic features of ionic liquids' polarity.