Structural behaviour of ionic liquids
Author(s)
Dolan, Andrew
Type
Thesis
Abstract
The ring flipping behaviour of some pyrrolidinium based ionic liquids has been examined
using variable temperature NMR spectroscopy, which allows the calculation
of the Gibb's free energy of activation of the ring flip. As it was impossible to
examine the neat ionic liquids, the work was carried out in solution. The role of
the solvent was investigated and its effect on the ring flip activation energy of N-methylpyrrolidinium
bis(trifluoromethylsulfonyl)imide was found to be accurately
described by the Kamlet-Taft parameters of the solvent. A range of ionic liquids
were examined in dimethylsulfoxide solutions. For a range of N-methylpyrrolidinium
ionic liquids there was no correlation found between any property of the system and
the ring flip activation energy. For a range of N-alkylpyrrolidinium hydrogensulfate
ionic liquids there was a positive correlation between the ring flip activation energy
and the free volume of the solution. While the free volume term correlates well, it
is believed to be indicative of some underlying entropic effect.
A range of 1-alkyl-3-methylimidazolium and 1,3-dialkylimidazolium ionic liquids
were examined using small angle X-Ray diffractometry. It was found that 1-alkyl-3-
methylimidazolium thiocyanates have a unique pre-peak in their diffraction patterns,
the structural origin of this peak is a repeating structure that is about twice the
length of the cation. Ionic liquids with other anions reported to date, and those
studied here, all have a pre-peak originating from a repeating structure that is
about the length of the cation. This strongly suggests 1-alkyl-3-methylimidazolium
thiocyanates have a different liquid structure than other ionic liquids. A pre-peak
was found in 1-butyl-3-methylimidazolium thiocyanate, which is the first report of
a pre-peak in an imidazolium based IL with such a short alkyl chain. It was also
found that 1,3-dihexylimidazolium ionic liquids have two peaks in the very small
angle regime. It was not possible to precisely determined the structural origin of
these peaks, however there are two possible explanations. Either first and second
order diffraction peaks of a repeating structure about twice the length of cation are
being seen, or there are two different structures being formed in the liquid, one of
which repeats on the length scale of one cation, the other of which repeats on the
length scale of two cations.
using variable temperature NMR spectroscopy, which allows the calculation
of the Gibb's free energy of activation of the ring flip. As it was impossible to
examine the neat ionic liquids, the work was carried out in solution. The role of
the solvent was investigated and its effect on the ring flip activation energy of N-methylpyrrolidinium
bis(trifluoromethylsulfonyl)imide was found to be accurately
described by the Kamlet-Taft parameters of the solvent. A range of ionic liquids
were examined in dimethylsulfoxide solutions. For a range of N-methylpyrrolidinium
ionic liquids there was no correlation found between any property of the system and
the ring flip activation energy. For a range of N-alkylpyrrolidinium hydrogensulfate
ionic liquids there was a positive correlation between the ring flip activation energy
and the free volume of the solution. While the free volume term correlates well, it
is believed to be indicative of some underlying entropic effect.
A range of 1-alkyl-3-methylimidazolium and 1,3-dialkylimidazolium ionic liquids
were examined using small angle X-Ray diffractometry. It was found that 1-alkyl-3-
methylimidazolium thiocyanates have a unique pre-peak in their diffraction patterns,
the structural origin of this peak is a repeating structure that is about twice the
length of the cation. Ionic liquids with other anions reported to date, and those
studied here, all have a pre-peak originating from a repeating structure that is
about the length of the cation. This strongly suggests 1-alkyl-3-methylimidazolium
thiocyanates have a different liquid structure than other ionic liquids. A pre-peak
was found in 1-butyl-3-methylimidazolium thiocyanate, which is the first report of
a pre-peak in an imidazolium based IL with such a short alkyl chain. It was also
found that 1,3-dihexylimidazolium ionic liquids have two peaks in the very small
angle regime. It was not possible to precisely determined the structural origin of
these peaks, however there are two possible explanations. Either first and second
order diffraction peaks of a repeating structure about twice the length of cation are
being seen, or there are two different structures being formed in the liquid, one of
which repeats on the length scale of one cation, the other of which repeats on the
length scale of two cations.
Date Issued
2013-02
Date Awarded
2013-06
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Welton, Tom
Publisher Department
Chemistry
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)