T. Fujimori, K. Fujii, R. Kanzaki
Mar 15, 2007
Citations
4
Influential Citations
65
Citations
Journal
Journal of Molecular Liquids
Abstract
Abstract Conformational structure of the N-butyl-N-methyl-pyrrolidinium (P14+) ion within its bis(trifluoromethanesulfonyl) imide (TFSI−) and bromide salts has been studied by means of DFT calculations and Raman spectroscopy. The P14+ ion gives various types of conformations with respect to the pyrrolidinium ring and N-butyl group. DFT calculations indicate that, among others, the eq- and ax-envelope conformers with the N-butyl group at equatorial and axial positions, respectively, against planar C4 atoms of the envelope pyrrolidinium ring (–NCH2CH2CH2CH2–) are relatively stable, and the former gives the global minimum. It revealed by comparing observed and calculated Raman spectra that the P14+ ion is present mainly as the ax-envelope conformer in the P14+Br− crystal, whilst the eq- and ax-envelope conformers are present in equilibrium in the P14+TFSI− ionic liquid. The presence of conformational equilibrium is further supported by Raman spectra measured by varying temperature. It is also established that conformation of the N-butyl group is restricted to the trans-TT, in which the butyl group locates trans against its nearest carbon atom in the pyrrolidinium ring, and all carbon atoms in the butyl chain are located trans each other.