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

Abstract

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 unsymmetrical boat conformations. Additional potential barriers to interconversion, resulting from pyramidal inversion of the nitrogen atom, were also revealed.

Revealing halogen bonding interactions with anomeric systems: An ab initio quantum chemical studies

“…The interaction of interhalogen compounds with the axial and equatorial lone-pairs of tetrahydro-1,3-oxazine has been studied. The un-substituted tetrahydro-1,3-oxazine was reported to exist mainly as chair conformer with the axial N-H bond [26].…”

Conformational analysis of 3-methyltetrahydro-1,3-oxazine

“…Noteworthily, the latter conformer was unstable in the case of unsubstituted tetrahydro-1,3-oxazine; in the course of energy minimization it was irreversibly converted into the 2,5-Т а form [34].…”

“…In particular, computer simulation in the frame of HF/6-31G(d) approximation has demonstrated that there are seven minima on the potential energy surface of unsubstituted tetrahydro-1,3-oxazine. The corresponding conformations were axial (global minimum) and equatorial chair and five flexible forms: two 1,4-twist-(1,4-Т), two 2,5-twist-(2,5-Т), and one 3,6-twist-(3,6-Т) [34]. This work aimed to perform conformational analysis of 3-methyltetrahydro-1,3-oxazine I in the frame of the nonempirical HF/6-31G(d) approximation as implemented in HyperChem software [35], the hybrid DFT method PBE/3z, and the RI-МР2/λ2 method (the latter two available in PRIRODA software package [36]).…”