ENERGETICAL an‎d STRUCTURAL INVESTIGATION FOR EQUATORIAL/AXIAL CONVERSION OF DIFFERENT SUBSTITUENTS ON PIPERIDINE an‎d PHOSPHORINANE: A THEORETICAL STUDY

Equatorial/axial conversion in piperidine and phosphorinane with different substituents were investigated with great details. Three possible routes, i.e. heteroatom inversion and two ring inversion type were considered. Ring conversion can occur via two pathways one starts with ring flattening from the heteroatom site (nitrogen in piperidine and phosphorous in phosphorinane) and the other initiates by ring flattening in the C4 position, facing the nitrogen/ phosphorous site. Density functional theory calculations are applied at B3LYP/6-311+G (d, p)// B3LYP/6-31G (d) level. The feasibility of equatorial/axial conversion for the substituted piperidine rings was found to be in the order of H>CH3>Cl~OH~F, whereas for phosphorinane it turns out to be as F>OH>Cl~H~CH3. In the piperidine derivatives hydrogen and methyl substituents the atom inversion route is dominant process while the other substituents (Cl, F, OH) one of the two possible ring inversion is favored. For the phosphorinane, however, ring inversion is the favored route for all substituents.