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 wereinvestigated with great details. Three possible routes, i.e. heteroatom inversion and two ring inversiontype were considered. Ring conversion can occur via two pathways one starts with ring flatteningfrom the heteroatom site (nitrogen in piperidine and phosphorous in phosphorinane) and the otherinitiates by ring flattening in the C4 position, facing the nitrogen/ phosphorous site. Densityfunctional theory calculations are applied at B3LYP/6-311+G(d,p)// B3LYP/6-31G(d) level. Thefeasibility of equatorial/axial conversion for the substituted piperidine rings was found to be in theorder of H>CH3>Cl~OH~F, whereas for phosphorinane it turns out to be as F>OH>Cl~ H~CH3. Inthe piperidine derivatives hydrogen and methyl substituents the atom inversion route is dominantprocess while the other substituents (Cl, F, OH) one of the two possible ring inversion is favored. Forthe phosphorinane, however, ring inversion is the favored route for all substituents.