Stereoelectronic interaction effects (associated with the anomeric effects) on the stability of the stereoisomers of 1,4,5,8-tetraoxadecalin, 1,4,5,8-tetrathiadecalin and 1,4,5,8-tetraselenadecalin. An ab initio study and NBO analysis

Abstract

NBO analysis, hybrid-density functional theory (hybrid-DFT: B3LYP/6-311+G∗∗//HF/6-311+G∗∗) and ab initio molecular orbital (MO: MP2/6-311+G∗∗//HF/6-311+G∗∗) based methods were used to study the anomeric effects ( AE) on the stability of the cis- and trans-stereoisomers of 1,4,5,8-tetraoxadecalin ( 1), 1,4,5,8-tetrathiadecalin ( 2) and 1,4,5,8-tetraselenadecalin ( 3). The B3LYP/6-311+G∗∗//HF/6-311+G∗∗ results revealed that the cis-stereoisomers of compounds 1–3 are more stable than their trans-stereoisomers by about 4.26, 1.03 and 0.70 kcal mol −1, respectively. Also, the cis-stereoisomers of compounds 1–3 are more stable than their trans-stereoisomers by about 4.18, 2.11 and 01.18 kcal mol-1, respectively, as calculated at the MP2/6-311+G∗∗//HF/6-311+G∗∗ level of theory. In addition, HF/6-311+G∗∗//HF/6-311+G∗∗ results revealed that the Gibbs free energy difference ( G cis − G trans) values (e.g. GFED cis–trans) between the cis- and trans-stereoisomers decrease from compound 1 to compound 3. On the other hand, the NBO analysis of donor–acceptor (bond-antibond) interactions revealed that the anomeric effects ( AE) for compounds 1–3 are −22.08, −17.84 and −13.22 kcal mol −1, respectively. The decrease of the AE could fairly explain the decrease of the GFED cis–trans from compound 1 to compound 3. On the other hand, the decrease of the donor–acceptor interactions associated with LP axM1 → σ∗ C9–O8 electronic delocalizations could fairly explain the increase of occupancies of LP axM1 non-bonding orbitals and the decrease of occupancies of σ∗ C9–O8 anti-bonding orbitals from the cis-stereoisomers of compound 1 to compound 3.