Vibrational investigation of 1-cyclopentylpiperazine: A combined experimental and theoretical study

FT-IR and Raman spectra of 1-cyclopentylpiperazine (1cppp) have been experimentally examined in the region of 4000-200 cm^?1. The optimized geometric parameters, conformational equilibria, normal mode frequencies and corresponding vibrational assignments of 1cppp (C₉H₁₈N₂) are theoretically examined by means of B3LYP hybrid density functional theory (DFT) method together with 6-31++G (d, p) basis set. On the basis of potential energy distribution (PED) reliable vibrational assignments have been made and the thermodynamics functions, highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) of 1cppp have been predicted. Calculations are employed for four different conformations in C₁ and C_s point groups of 1cppp in gas phase. Comparison between the experimental and theoretical results indicates that B3LYP method is able to provide satisfactory results for predicting vibrational frequencies and the structural parameters, vibrational frequencies and assignments. Furthermore, C₁ (equatorial-axial) point group has been found as the most stable conformer of 1cppp.