Stereoelectronic interaction effects on the conformational properties of hydrogen peroxide and its analogues containing S and Se atoms: An ab initio, hybrid-DFT study and NBO analysis

Abstract

Ab initio molecular orbital (MP2/6-311+G**//MP2/6-31G+G**) and hybrid-density functional theory (B3LYP/6-311+G**//MP2/6-311+G**) methods and NBO analysis were used to study the stereoelectronic interaction effects on the conformational properties of hydrogen peroxide ( 1), hydrogen disulfide ( 2) and hydrogen diselenide ( 3). The results showed that the Gibbs free energy difference ( G T − G S ) values at 298.15 K and 1 atm between the skew ( S) and trans ( T) conformations (Δ G T– S ) increase from compound 1 to compound 2 but decrease from compound 2 to compound 3. The C conformations of compounds 1– 3 are less stable than their S and T conformations. Based on these results, the racemization processes of the axial symmetrical ( C 2 symmetry) conformations of compounds 1– 3 take place via their T conformations. Based on the optimized ground state geometries using the MP2/6-311+G** level of theory, the NBO analysis of donor–acceptor (bond–antibond) interactions revealed that the stabilization (resonance) energy associated with LP 2M2 → σ* M3-H4 electronic delocalization for the S conformations of compounds 1– 3 are 1.35, 5.94 and 4.68 kcal mol −1, respectively. There is excellent agreement between the variations of the calculated Δ G T– S and stabilization (resonance) energies associated with LP 2M2→σ* M3-H4 electronic delocalization for the S conformations of compounds 1– 3. The correlations between resonance energies, orbital integrals, dipole moments, bond orders, structural parameters and conformational behaviors of compounds 1– 3 have been investigated. Test were made of complete basis set methods (CBS-QB3, CBS-4 and CBS-Q), the first two gave results essentially indistinguishable from those we used, but the CBS-Q results were in disagreement with experimental and other theoretical results.