Hon Man Yau

Ionic liquids: just Molten salts after all?

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.

Investigating the origin of entropy-derived rate accelerations in ionic liquids

The effects on the rate and activation parameters of a series of Menschutkin processes on changing from a molecular solvent to an ionic liquid were investigated. The removal of delocalised pi-systems from the reagents does not affect the change in activation parameters on changing solvent. In each of the cases investigated, rate accelerations observed on moving to the ionic liquid could be attributed to an increase in reaction entropy. This suggests a specific interaction of the ionic liquid with the nucleophilic centre, rather than the delocalised pi-systems of either the electrophile or the nucleophile.

Does the cation really matter? The effect of modifying an ionic liquid cation on an SN2 process

The rate of reaction of a Menschutkin process in a range of ionic liquids with different cations was investigated, with temperature-dependent kinetic data giving access to activation parameters for the process in each solvent. These data, along with molecular dynamics simulations, demonstrate the importance of accessibility of the charged centre on the cation and that the key interactions are of a generalised electrostatic nature.

Using Supramolecular Binding Motifs To Provide Precise Control over the Ratio and Distribution of Species in Multiple Component Films Grafted on Surfaces: Demonstration Using Electrochemical Assembly from Aryl Diazonium Salts

Supramolecular interactions between two surface modification species are explored to control the ratio and distribution of these species on the resultant surface. A binary mixture of aryl diazonium salts bearing oppositely charged para-substituents (either -SO3(-) or -N(+)(Me)3), which also reduce at different potentials, has been examined on glassy carbon surfaces using cyclic voltammetry and X-ray photoelectron spectroscopy (XPS). Striking features were observed: (1) the two aryl diazonium salts in the mixed solution undergo reductive adsorption at the same potential which is distinctively less negative than the potential required for the reduction of either of the two aryl diazonium salts alone; (2) the surface ratio of the two phenyl derivatives is consistently 1:1 regardless of the ratio of the two aryl diazonium salts in the modification solutions. Homogeneous distribution of the two oppositely charged phenyl species on the modified surface has also been suggested by XPS survey spectra. Diffusion coefficient measurements by DOSY NMR and DFT based computation have indicated the association of the two aryl diazonium species in the solution, which has led to changes in the molecular orbital energies of the two species. This study highlights the potential of using intermolecular interactions to control the assembly of multicomponent thin layers.

Reaction mechanisms: polar reactions

Highlights of mechanistic work pertaining to polar reactions published in 2012 are provided in this report. Such reactions cover a wide range of biologically, chemically and industrially-relevant processes, and although they have been broadly classified here, a number could span one or more general categories. Areas such as biological reactions and their models, metal ion-catalysed reactions, and ionic-mediated reactions are all featured.