title: HF, MP2 and DFT calculations and spectroscopic study of the vibrational and conformational properties of N-diethylendiamine.
abstract: 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.
authors.affiliation: Laboratoire de Physique Appliquée, Faculté des Sciences de Sfax, BP 802, Sfax, Tunisia. slimlpa@yahoo.fr
authors.forename: S
authors.initials: S
authors.lastname: Elleuch
authors.forename: H
authors.initials: H
authors.lastname: Feki
authors.forename: Y
authors.initials: Y
authors.lastname: Abid
mesh_terms: D003959:Diamines / Q000737:chemistry*; D005030:Ethylenes / Q000737:chemistry*; D008956:Models, Chemical; D008968:Molecular Conformation; D013059:Spectrum Analysis, Raman; D013816:Thermodynamics; D014732:Vibration
chemical_list: D003959:Diamines; D005030:Ethylenes; C526670:N-diethylendiamine