## 4 Conclusions  
In this study, we have investigated the role of the C(2) position in imidazolium-based ionic liquids with highly symmetric anions. A series of compounds in which the C(2) position was either protonated or methylated was analyzed with respect to the thermal and structural (IR, Raman, and H-NMR) properties. In the ILs exhibiting a proton at C(2), this functional group represents the predominant site for interionic interactions via hydrogen bonding. When the proton is replaced by a methyl group, this possibility is removed and the anion rearranges itself at the opposite side of the ring. It forms a new hydrogen bond with either the C(4) or C(5) proton. The split of the initially degenerate C(4)/(5)-H stretching band into red- and blue-shifted new peaks suggests that only one of the two aromatic CH groups is involved in this hydrogen bond. With increased diameter of the anion,  
Figure 5: Schematic interaction geometries of (**a**) [MMPrIm\({}^{+}\)][I\({}^{-}\)] and (**b**) [MMPrIm\({}^{+}\)][BF\({}_{4}{}^{-}\)]. The geometries were energetically optimized using the MM2 function of ChemDraw, but they may not accurately represent the true configuration due to the simplistic underlying model. They are meant to serve as a general illustration of the interaction. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Assignment** & \begin{tabular}{c} \(\left[\text{MPrIm}{}^{+}\right]\) \\ \(\left[\text{I}{}^{-}\right]\) \\ \end{tabular} & \begin{tabular}{c} \(\left[\text{MPrIm}{}^{+}\right]\) \\ \(\left[\text{I}{}^{-}\right]\) \\ \end{tabular} & \begin{tabular}{c} \(\left[\text{MPrIm}{}^{+}\right]\) \\ \(\left[\text{BF}_{4}{}^{-}\right]\) \\ \end{tabular} & \begin{tabular}{c} \(\left[\text{MPrIm}{}^{+}\right]\) \\ \(\left[\text{BF}_{6}{}^{-}\right]\) \\ \end{tabular} & \
\begin{tabular}{c} \(\left[\text{MPrIm}{}^{+}\right]\) \\ \(\left[\text{PF}_{6}{}^{-}\right]\) \\ \end{tabular} &
\begin{tabular}{c} \(\left[\text{MPrIm}{}^{+}\right]\) \\ \(\left[\text{PF}_{6}{}^{-}\right]\) \\ \end{tabular} \\ \hline C(2)–H & 9.08 & & 9.05 & & 9.21 & \\ C(4)–H & 7.72 & 7.63 & 7.71 & 7.33–7.34 & 7.82 & 7.31–7.34 \\ C(5)–H & 7.67 & 7.60 & 7.65 & 7.26 & 7.75 & 7.24–7.26 \\ C(6)–H & 3.86 & 3.75 & 3.85 & 3.66 & 3.87 & 3.67 \\ C(7)–H & 4.11–4.14 & 4.06–4.09 & 4.10–4.14 & 3.85–3.89 & 4.13–4.17 & 3.84–3.90 \\ C(8)–H & 1.79–1.84 & 1.71–1.77 & 1.78–1.83 & 1.48–1.55 & 1.76–1.82 & 1.51–1.59 \\ C(9)–H & 0.85–0.88 & 0.86–0.89 & 0.85–0.88 & 0.62–0.65 & 0.81–0.85 & 0.63–0.69 \\ C(10)–H & & 2.58 & & 2.49 & & 2.48–2.50 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: \({}^{1}\)H-NMR peaks and assignments. additional interactions seem to take place with the propyl side chain. This is suggested by the NMR spectra. The spectroscopic observations indicate an increase in the homogeneity of the electron distribution upon methylation. This gain in symmetry is reflected at the macroscopic level by an increase in viscosity and melting point. In other words, the methylated ILs are characterized by lower fluid mobility and easier arrangement in a solid crystalline network. Similar behavior has also been found for imidazolium-based ILs with nonsymmetric anions, thus it appears to be a universal phenomenon. A further interesting observation was that methylation of the C(2) position resulted in an increased decomposition temperature. This implies that the changes in the chemical structure and interactions lead to enhanced stability of the compounds. Therefore it may be speculated that the thermal decomposition likely starts at the C(2) moiety. Analyzing the decomposition in more detail would require coupling the TGA with FTIR and mass spectrometry analysis of the blue gas. Conceptualization: D.V., H.B., and B.H. ; methodology: H.B., S.B., O.A., and A.P. ; synthesis: H.B. and D.V. ; characterization: S.B., O.A., and O.P. ; data analysis: B.H., J.K., O.P., and S.B. ; writing-original draft preparation: B.H. and O.P. ; writing-review and editing: J.K. and A.P. ; supervision: H.B., E.B., and M.R. This research received no external funding.