While there has been much effort in recent years to characterise ionic liquids in terms of parameters that are well described for molecular solvents, using these to explain reaction outcomes remains problematic. Herein we propose that many reaction outcomes in ionic liquids may be explained by considering the electrostatic interactions present in the solution; that is, by recognising that ionic liquids are salts. This is supported by evidence in the literature, along with studies presented here.

Ionic liquids are frequently touted as alternatives to traditional molecular solvents but are limited in their applicability as the outcome of reactions may be altered on moving from a molecular to an ionic solvent. This manuscript summarizes our progress towards a predictive framework through understanding how ionic solvents affect organic processes, with an emphasis on how these findings might be applied. Particularly, we will consider the importance of the mole fraction of the ionic liquid used, including some hitherto undisclosed results, as well as the importance of understanding the key interactions of the solvent with the components along the reaction coordinate.

The effect of a series of ionic liquids on the regioselectivity of the azide-alkyne cycloaddition process was investigated, demonstrating an increased selectivity for the least hindered triazole. The effects of an ionic liquid on the activation parameters for the process were determined and found to be intermediate between coordinating and non-coordinating salts. The importance of knowing the water content of the system is demonstrated by marked changes in the activation parameters in the presence of small concentrations of water.

A series of aromatic hydrocarbons were investigated so as to compare the reactivity of corannulene with planar aromatic hydrocarbons. Corannulene was found to be more reactive than benzene, naphthalene and triphenylene to Friedel-Crafts acylation whilst electrophilic aromatic bromination was also used to confirm that triphenylene was less reactive than corannulene and that pyrene, perylene and acenaphthene were more so. The stabilisation of a neighbouring carbocation by the various aromatic systems was investigated through consideration of the rates of methanolysis of a series of benzylic alcohols. The reactivity series was found to parallel that observed for the electrophilic aromatic substitutions and both series are supported by computational studies. As such, a reactivity scale was devised that showed that corannulene was less reactive than would be expected for an aromatic planar species of similar pi electron count.

A range of substituted benzhydrols and fluorenols were prepared and subjected to acid catalysed methanolysis. Analysis of the rates of each of these processes showed correlation with Hammett σ(+) parameters as is consistent with the significant build-up of positive charge adjacent to the ring. In combination with the similarity of the electronic susceptibility of the processes, these data suggest that both reactions proceed through a unimolecular rate-determining step. This shows that the effect of fusion of the phenyl systems (and hence potentially introducing an antiaromatic carbocation intermediate) is only to slow the rate of reaction rather than change the mechanism of the process.