title: Novel chiral ionic liquids: physicochemical properties and investigation of the internal rotameric behaviour in the neat system.
abstract: Optically active S-alkyl-N,N'-bis((S)-1-phenylethyl)thiouronium salts, abbreviated as (S)-[C(n)petu]Y (where Y is an anion; n = 1, 2, 3, 4, 6, 8, 10, 12 or 16), have been prepared and studied by a broad spectrum of analyses. This consists of density, viscosity, and conductivity determination, followed by a discussion of relevant correlations. Unusual trends depending on the S-alkyl chain length were documented for (S)-[C(n)petu][NTf2] series (where [NTf2](-) = bis{(trifluoromethyl)sulfonyl}amide), including the viscosity decreasing with increasing chain length, and the conductivity showing a maximum between the S-butyl and the S-hexyl derivative. In addition, a hindered rotamerism of the thiouronium cation in dmso-d6 solution was recognised by (1)H and (13)C NMR techniques. Thorough analysis of NMR spectra confirmed that the main contribution comes from rotation about the partial double C-S bond. For the first time, a neat thiouronium ionic liquid system has been subjected to quantitative analysis of hindered rotamerism by dynamic NMR coalescence studies, with estimated activation energy for rotation of 63.9 ± 0.4 kJ mol(-1). Finally, the application of (S)-[C(n)petu]Y salts as chiral discriminating agents for carboxylates by (1)H NMR spectroscopy was further investigated, demonstrating the influence of the S-alkyl chain length on chiral recognition; (S)-[C2petu][NTf2] ionic liquid with the mandelate anion gave the best results.
authors.affiliation: QUILL Research Centre, School of Chemistry and Chemical Engineering, The Queen's University of Belfast, Belfast BT9 5AG, Northern Ireland, UK. mforeiter01@qub.ac.uk n.gunaratne@qub.ac.uk.
authors.forename: Magdalena B
authors.initials: MB
authors.lastname: Foreiter
authors.forename: H Q Nimal
authors.initials: HQ
authors.lastname: Gunaratne
authors.forename: Peter
authors.initials: P
authors.lastname: Nockemann
authors.forename: Kenneth R
authors.initials: KR
authors.lastname: Seddon
authors.forename: Geetha
authors.initials: G
authors.lastname: Srinivasan