Ab Initio conformational analysis of tetrahydro-1,3-oxazine

Nonempirical RHF/STO-3G and 6-31G(d) studies on conformational behavior of tetrahydro-1,3- oxazine showed that interconversion between the axial (global minimum) and equatorial chair conformers can follow five independent pathways. The potential energy surface contains seven minima corresponding to chair and twist conformers, as well as seven transition states having sofa, half-chair, and symmetrical and unsym- metrical boat conformations. Additional potential barriers to interconversion, resulting from pyramidal inversion of the nitrogen atom, were also revealed.