Vibrational spectra, DFT calculations, conformational stabilities and assignments of the fundamentals of the 1-butylpiperazine

FT-IR and FT-Raman spectra of 1-butylpiperazine (1bpa) were experimentally recorded in the region of 4000-10 cm−1 and 4000-100 cm−1, respectively. The optimized geometric parameters, conformational equilibria, normal mode frequencies and corresponding vibrational assignments of 1bpa (C8H18N2) are theoretically examined by means of B3LYP hybrid density functional theory (DFT) method together with 6-31++G(d,p) basis set. Also, reliable conformational investigation and vibrational assignments have been performed by the potential energy surface (PES) and potential energy distribution (PED) analysis, respectively. Calculations are made for four possible conformations. According to the experimental and theoretical data, density functional B3LYP method provides reliable results for predicting vibrational wavenumbers and equatorial-equatorial conformer is considered to be the most stable form of 1bpa.