Ab Initio Calculations of the Conformational Preferences of 1,3-Oxathiane S-Oxide and its Analogs Containing S and SE Atoms—Evidence for Stereoelectronic Interactions Associated with the Anomeric Effects

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Stereoelectronic interactions associated with the AE and also the conformational and structural properties of 1,3-oxathiane S-oxide (1), 1,3-dithiane S-oxide (2), 1,3-thiaselenane S-oxide (3), 1,3-oxaselenane Se-oxide (4), 1,3-thiaselenane Se-oxide (5), and 1,3-diselenane Se-oxide (6) were investigated using quantum mechanical methods. These compounds were fully optimized at the B3LYP/6 – 311 + G** and HF/6 – 311 + G** levels of theory. The Gibbs Free Energy, Enthalpy, and Entropy differences (i.e., ΔG, ΔH, and ΔS) between the axial and equatorial conformations were calculated at the B3LYP/6 – 311 + G** and HF/6 – 311 + G** levels of theory. The decrease of the AE is corresponding to the decreases of calculated Δ(G ax – G eq) value of the above mentioned compounds. The calculated AE values are more significant for the justification of the conformational dominances of the compounds than steric effects. In this work, the relations between the Anomeric Effects, donor and acceptor orbital energies, occupancies, structural parameters, dipole–dipole interactions, and conformational behavior of the compounds have been studied.