Structural and spectral properties of quinolizidine alkaloids: quantum chemical calculations

Structural and spectroscopic properties of quinolizidine alkaloids lupinine and epilupinine stereoisomers were studied theoretically. The influence of the calculation method and structural change in the molecule on the results of geometry and other properties of compounds was considered. The equilibrium geometry, harmonic vibrational frequencies and infrared intensities were obtained by means of density functional theory (DFT/B3LYP) calculations with the splitvalence medium-sized 6-31G(d) basis and Dunning’s correlation consistent basis set cc-pVDZ. From the optimized structure of the (+)-lupinine and (+)-epilupinine molecules, geometric parameters were compared with the literature X-ray experimental data. Structural and vibrational parameters for the (-)-lupinine and (-)-epilupinine molecules are predicted by theoretical calculations at B3LYP/6-31G(d) and B3LYP/cc-pVDZ levels of theory. Some physical characteristics for the title compounds, such as total electronic energy, zero-point energy, rotational constants and dipole moments were also defined by DFT methods. The thermodynamic functions of the title compounds were performed at the same theory levels. Stationary points are identified by the solution of the oscillatory problem.