Heimer Norman E, Wilkes John S, Wahlbeck Phillip G, Carper W Robert
Department of Chemistry, USAF Academy, Colorado 80840-6230, USA.
J Phys Chem A. 2006 Jan 26;110(3):868-74. doi: 10.1021/jp056045+.
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.
一种从粘性溶液中芳香族碳的13C自旋晶格弛豫数据获取分子重取向动力学的新方法，被应用于离子液体1-乙基-3-甲基咪唑鎓丁磺酸盐（[EMIM]BSO3）中阳离子和阴离子的13C弛豫数据。利用13C假旋转相关时间，通过一个综合的各向同性偶极和核Overhauser效应（NOE）方程来计算校正后的最大NOE因子。然后，这些校正后的最大NOE因子被用于确定咪唑鎓环中每个芳香族13C核的总弛豫速率的偶极弛豫速率部分。将旋转相关时间与粘度数据进行比较，结果表明在278至328 K的温度范围内，[EMIM]BSO3发生了几次相变。采用对斯托克斯-爱因斯坦-德拜（SED）模型的修正来确定1-乙基-3-甲基咪唑鎓阳离子的分子半径。胡-茨万齐格校正得到的阳离子半径与密度泛函理论（DFT）气相计算B3LYP/(6-311+G(2d,p))的结果相当。获得了咪唑鎓阳离子中环以及紧邻的亚甲基和甲基碳，以及阴离子中最靠近磺酸根基团的三个碳原子的化学位移各向异性值Δσ。
