FT-IR spectroscopic, AM1 and PM3 computational studies of conformation of natural products: cytisine

Infrared spectra were recorded for cytisine (1) and its model compounds: N-methyl-2-pyridone (2) and piperidine (3) in solution. Eight solvents of different polarity, polarizability and acid–base properties: CCl4, CS2, CHCl3, CDCl3 (for comparison with the NMR spectra), CH2Cl2, MeOH, Et2O and Et3N were chosen. Experimental FT-IR spectra were analysed with the help of those calculated for isolated derivatives at the AM1 and PM3 levels. Influence of environment on the conformational preferences in solvated cytisine was discussed and compared with those in the solid state (X-ray measurements) and in the gas phase (quantum-mechanical calculations).