Conformational structure of room temperature ionic liquid N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl) imide -: Raman spectroscopic study and DFT calculations
Conformational structure of room temperature ionic liquid N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl) imide -: Raman spectroscopic study and DFT calculations
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DOI：
10.1016/j.molliq.2006.08.054
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发表时间：
2007-03-15
影响因子：
6
通讯作者：
Ishiguro, Shin-ichi
中科院分区：
文献类型：
--
作者：
Fujimori, Takao;Fujii, Kenta;Ishiguro, Shin-ichi
用密度泛函理论和拉曼光谱研究了N-丁基-N-甲基-吡咯烷鎓（P-14（+））离子在其二（三氟甲磺酰基）酰亚胺（TFSI-）和溴化物盐中的构象结构. P-14（+）离子相对于吡咯烷鎓环和N-丁基基团给出各种类型的构象。DFT计算表明，正丁基分别位于赤道和轴向位置的eq-和ax-包络构象对包络吡咯烷鎓环（-NCH 2CH 2CH 2CH 2-）的平面C-4原子相对稳定，前者给出全局最小值.通过比较观测和计算的拉曼光谱，发现P-14（+）离子在P14+Br-晶体中主要以轴包络构象存在，而在P14+TFSI-离子液体中平衡存在eq-和轴包络构象。通过改变温度测量的拉曼光谱进一步支持构象平衡的存在。还确定了N-丁基的构象限于反式-TT，其中丁基相对于吡咯烷鎓环中最近的碳原子反式定位，并且丁基链中的所有碳原子彼此反式定位。(C)2006 Elsevier B. V.保留所有权利。
Conformational structure of the N-butyl-N-methyl-pyrrolidinium (P-14(+)) ion within its bis(trifluoromethanesulfonyl) imide (TFSI-) and bromide salts has been studied by means of DFT calculations and Raman spectroscopy. The P-14(+) ion gives various types of conformations with respect to the pyrrolidinium ring and N-butyl group. DFT calculations indicate that, among others, the eq- and ax-envelope conformers with the N-butyl group at equatorial and axial positions, respectively, against planar C-4 atoms of the envelope pyrrolidinium ring (-NCH2CH2CH2CH2-) are relatively stable, and the former gives the global minimum. It revealed by comparing observed and calculated Raman spectra that the P-14(+) ion is present mainly as the ax-envelope conformer in the P14+Br- crystal, whilst the eq- and ax-envelope conformers are present in equilibrium in the P14+TFSI- ionic liquid. The presence of conformational equilibrium is further supported by Raman spectra measured by varying temperature. It is also established that conformation of the N-butyl group is restricted to the trans-TT, in which the butyl group locates trans against its nearest carbon atom in the pyrrolidinium ring, and all carbon atoms in the butyl chain are located trans each other. (C) 2006 Elsevier B.V. All rights reserved.