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首页> 外文期刊>The journal of physical chemistry, B. Condensed matter, materials, surfaces, interfaces & biophysical >Conformational analysis of 1-butyl-3-methylimidazolium by CCSD(T) level ab initio calculations: Effects of neighboring anions
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Conformational analysis of 1-butyl-3-methylimidazolium by CCSD(T) level ab initio calculations: Effects of neighboring anions

机译：通过CCSD（T）级从头算起的1-丁基-3-甲基咪唑鎓构象分析：邻近阴离子的影响

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摘要

Conformational energies for the butyl group of 1-butyl-3-methylimidazolium (bmim) were calculated by high-level ab initio methods. Estimated relative energies for the TT, GT and G'T rotamers of an isolated bmim cation at the CCSD(T)/cc-pVTZ level are 0.0 -0.02 and -0.50 kcal/mol, respectively. The close contact of a Cl anion to the C-2-H of imidazolium considerably increases the relative stability of the GT rotamer. Estimated relative energies for the three rotamers of the [bmim]Cl complex, in which the Cl anion exists close to the C-2-H, are 0.0, -1.61 and -0.25 kcal/mol, respectively. The GT rotamer is favored by the strong attractive electrostatic interaction between the bmim cation and Cl anion. The C-2-H group in the GT rotamer has a larger positive charge Compared with those in the TT and G'T rotamers. The contact of a Br anion to the C-2-H also stabilizes the GT rotamer. The effects of the Cl anion close to the C-4-H and C-5-H are small. The anion effects suggest that the GT rotamer is the most stable in ionic liquids. The positive charge on imidazolium ring does not largely change the conformational energies. Estimated relative energies for the three rotamers of N-butylimidazole (0.0, -0.29 and -0.75 kcal/mol, respectively) are not largely different from those for isolated bmim. Calculated MP2/cc-pVTZ level torsional potential for the C-im-N-im-C-C bond has a minimum when the torsional angle is close to 90 degrees. Coplanar conformation is not a stable structure. Calculated torsional barrier height between the two nonplanar minima is less than 1 kcal/mol.
机译：通过高级从头算法计算了1-丁基-3-甲基咪唑鎓（bmim）丁基的构象能。在CCSD（T）/ cc-pVTZ水平下，孤立的bmim阳离子的TT，GT和G'T旋转异构体的估计相对能量分别为0.0 -0.02和-0.50 kcal / mol。 Cl阴离子与咪唑的C-2-H紧密接触大大提高了GT旋转异构体的相对稳定性。 Cl阴离子存在于C-2-H附近的[bmim] Cl络合物的三个旋转异构体的估计相对能量分别为0.0，-1.61和-0.25 kcal / mol。 GT旋转异构体因bmim阳离子和Cl阴离子之间的强吸引力静电相互作用而受到青睐。与TT和G'T旋转异构体相比，GT旋转异构体中的C-2-H基团具有更大的正电荷。 Br阴离子与C-2-H的接触也会稳定GT旋转异构体。 Cl阴离子接近C-4-H和C-5-H的作用很小。阴离子效应表明GT旋转异构体在离子液体中最稳定。咪唑环上的正电荷不会大大改变构象能。 N-丁基咪唑的三个旋转异构体（分别为0.0，-0.29和-0.75 kcal / mol）的估计相对能量与孤立的bmim的相对能量没有太大差异。当扭转角接近90度时，C-im-N-im-C-C键的计算出的MP2 / cc-pVTZ级扭转势最小。共面构象不是稳定的结构。两个非平面最小值之间的计算得出的扭转势垒高度小于1 kcal / mol。

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