Theoretical investigation of vinylogous anomeric effect on 4-halo-4-H-pyran and 4-halo-4-H-thiopyran molecules

In this study, the stability of the 4-halo-4-H-pyran and 4-halo-4-H-thiopyran molecules in planar and puckered conformations was investigated in the B3LYP/6-311++G(d,p) level of theory. The total energy, dipole moment, the energies of frontier orbitals, and HOMO–LUMO gaps of the molecules were calculated. Natural bond orbital (NBO) analysis was used to illustrate vinylogous anomeric effect on the puckering of ring. The responsible interactions of this effect were determined. The interaction energy, off-diagonal elements and dipole moment values of their NBO were calculated. In addition, total steric exchange energy values of theses interaction were evaluated.