A new method of obtaining molecular reorientational dynamics from 13C spin-lattice relaxation data of aromatic carbons in viscous solutions is applied to 13C relaxation data of the ionic liquid, 1-methyl-3-nonylimidazolium hexafluorophosphate ([MNIM]PF6). Spin-lattice relaxation times (13C) are used to determine pseudorotational correlation times for the [MNIM]PF6 ionic liquid. Pseudorotational correlation times are used to calculate corrected maximum NOE factors from a combined isotropic dipolar and nuclear Overhauser effect (NOE) equation. These corrected maximum NOE factors are then used to determine the dipolar relaxation rate part of the total relaxation rate for each aromatic 13C nucleus in the imidazolium ring. Rotational correlation times are compared with viscosity data and indicate several [MNIM]PF6 phase changes over the temperature range from 282 to 362 K. Modifications of the Stokes-Einstein-Debye (SED) model are used to determine molecular radii for the 1-methyl-3-nonylimidazolium cation. The Hu-Zwanzig correction yields a cationic radius that compares favorably with a DFT gas-phase calculation, B3LYP/(6-311+G(2d,p)). Chemical shift anisotropy values, delta sigma, are obtained for the ring and immediately adjacent methylene and methyl carbons in the imidazolium cation. The average delta sigma values for the imidazolium ring carbons are similar to those of pyrimidine in liquid crystal solutions.

The process of obtaining molecular reorientational dynamics from 13C spin−lattice relaxation data is simplified for aromatic carbons in viscous solutions. Spin−lattice relaxation times (13C) are used to determine pseudorotational correlation times for the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]). The pseudorotational correlation times are used to calculate corrected maximum nuclear Overhauser effect (NOE) factors from a combined isotropic dipolar and NOE equation. These corrected maximum NOE factors are then used to determine the dipolar relaxation rate part of the total relaxation rate for each 13C nucleus in the imidazolium ring. A consequence of this analysis is that a plot of the maximum NOE factors and the total spin−lattice relaxation times have minima at similar temperatures. Chemical shift anisotropy values, Δσ, for the aromatic carbons in the imidazolium cation are temperature dependent with maximum Δσ values at ca. the same temperature as observed for the spin−lattice relaxation times. The average Δσ values for the imidazolium ring carbons are similar to those of pyrimidine in liquid crystal solutions.

A new method of obtaining molecular reorientational dynamics from 13C spin-lattice relaxation data of aromatic carbons in viscous solutions is applied to 13C relaxation data of both the cation and anion in the ionic liquid, 1-ethyl-3-methylimidazolium butanesulfonate ([EMIM]BSO3). 13C pseudorotational correlation times are used to calculate corrected maximum NOE factors from a combined isotropic dipolar and nuclear Overhauser effect (NOE) equation. These corrected maximum NOE factors are then used to determine the dipolar relaxation rate part of the total relaxation rate for each aromatic 13C nucleus in the imidazolium ring. Rotational correlation times are compared with viscosity data and indicate several [EMIM]BSO3 phase changes over the temperature range from 278 to 328 K. Modifications of the Stokes-Einstein-Debye (SED) model are used to determine molecular radii for the 1-ethyl-3-methylimidazolium cation. The Hu-Zwanzig correction yields a cationic radius that compares favorably with a DFT gas-phase calculation, B3LYP/(6-311+G(2d,p)). Chemical shift anisotropy values, Deltasigma, are obtained for the ring and immediately adjacent methylene and methyl carbons in the imidazolium cation and for the three carbon atoms nearest to the sulfonate group in the anion.