Elleuch S, Feki H, Abid Y
Laboratoire de Physique Appliquée, Faculté des Sciences de Sfax, BP 802, Sfax, Tunisia.
Spectrochim Acta A Mol Biomol Spectrosc. 2007 Nov;68(3):942-7. doi: 10.1016/j.saa.2007.01.007. Epub 2007 Jan 19.
The conformational stability and vibrational modes of the N-diethylendiamine organic cation (N-DD(2+)) were studied by experimental (Raman) spectroscopy combined with theoretical calculations. Various ab initio theories were used: Hartree-Fock (HF) theory, Möller-Plesset second-order perturbation (MP2) theory and density functional theory (DFT). Three stable conformers of N-DD(2+), trans-trans, gauche-gauche and gauche-trans were calculated. A comparison between the computed structural parameters of the conformers at both levels of theory and the X-ray data was made. It is demonstrated that the N-DD(2+) cation adopts more probably the gauche-gauche conformation at room temperature. In order to make a more detailed interpretation of the low temperature phase transition of N-DDHP, the Raman spectra of N-DDHP were recorded at room and low temperature in the 200-3400 cm(-1) region. The vibrational frequencies of the different conformers of N-DD(2+) were also calculated using the DFT/B3LYP (6-31G(d)) level of theory. By comparison between the experimental and theoretical results, the conformational dynamic of the N-DD(2+) organic cation was confirmed. It is shown that the N-DD(2+) cation configuration changes from gauche-gauche conformer to gauche-trans conformer when decreasing the temperature.
通过实验（拉曼）光谱结合理论计算研究了N-二亚乙基二胺有机阳离子（N-DD(2+)）的构象稳定性和振动模式。使用了各种从头算理论：哈特里-福克（HF）理论、莫勒-普莱斯塞二阶微扰（MP2）理论和密度泛函理论（DFT）。计算出了N-DD(2+)的三种稳定构象异构体，反式-反式、gauche- gauche和gauche-反式。对两种理论水平下构象异构体的计算结构参数与X射线数据进行了比较。结果表明，N-DD(2+)阳离子在室温下更可能采用gauche- gauche构象。为了更详细地解释N-DDHP的低温相变，在室温及低温下记录了200 - 3400 cm(-1)区域内N-DDHP的拉曼光谱。还使用DFT/B3LYP（6-31G(d)）理论水平计算了N-DD(2+)不同构象异构体的振动频率。通过实验结果与理论结果的比较，证实了N-DD(2+)有机阳离子的构象动力学。结果表明，当温度降低时，N-DD(2+)阳离子构型从gauche- gauche构象异构体转变为gauche-反式构象异构体。
