Computational study of the anomeric effect in 2-[(4-substituted phenyl)seleno]-1,3-dithianes

The conformational equilibrium of 1,3-dithiane-2-selenol and 2-[(4-substituted phenyl)seleno]-1,3-dithianes with NO₂, H, CH₃, OCH₃ and N(CH₃)₂ as substituents has been studied with PM3 and HF/6-31G*. Both methods confirm the preference for the axial conformers for these compounds with electron witdrawing groups enhancing this trend. The structural parameters have been used to assess the presence of the endo and exo anomeric effects in the axial conformers. NBO analysis for 1,3-dithiane-2-selenol has shown that delocalization involving the sulfur and selenium lone pairs and the C2-Se anti-bonding orbital plays a role in stabilizing the axial conformer for this compound. Single point energy calculations in solution with HF/6-31G*//HF/6-31G* mimic the experimental results to a great extent.