title: Evidence for spin diffusion in a H,H-NOESY study of imidazolium tetrafluoroborate ionic liquids.
abstract: The ionic liquids 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]) and 1-methyl-3-propylimidazolium tetrafluoroborate ([PMIM][BF4]) were studied by H,H-NOESY NMR using a cross-relaxation matrix analysis. Cross-peak intensities are seen to increase with increasing mixing time. Experimental and theoretical hydrogen-hydrogen distances are in agreement at short mixing times (50 ms). Mixing times longer than 50 ms result in an increasing contribution of spin diffusion that produces unrealistically short hydrogen-hydrogen distances. Gas-phase ab initio molecular structures are obtained using Hartree-Fock (HF) and density functional theory (B3LYP) methods at the 6311 + G(2d,p) basis set level. The hydrogen-hydrogen distances obtained from the theoretical structures are in reasonable agreement with those calculated from the cross-relaxation matrices.
authors.affiliation: Department of Chemistry, USAF Academy, Colorado 80840-6230, USA.
authors.forename: Norman E
authors.initials: NE
authors.lastname: Heimer
authors.forename: Rico E
authors.initials: RE
authors.lastname: Del Sesto
authors.forename: W Robert
authors.initials: WR
authors.lastname: Carper
mesh_terms: D004058:Diffusion; D007093:Imidazoles / Q000737:chemistry*; D007477:Ions / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008956:Models, Chemical; D015394:Molecular Structure; D013113:Spin Labels; D013997:Time Factors
chemical_list: C499119:1-ethyl-3-methylimidazolium tetrafluoroborate; C499120:1-methyl-3-propylimidazolium tetrafluoroborate; D007093:Imidazoles; D007477:Ions; D013113:Spin Labels