Hybrid-DFT study and NBO interpretations of the conformational behavior of 1,2-dihalodisilanes

Abstract

Hybrid-density functional theory (B3LYP/Def2-TZVPP) based method and NBO<br />interpretation were used to investigate the conformational behavior of 1,2-dihalodisilanes<br />[halo=F (1), Cl (2), Br (3), I (4)]. The B3LYP/Def2-TZVPP results showed that the anti<br />conformations of compounds 1-4 are more stable than their corresponding gauche<br />conformations. The stability of the anti conformation compared to the gauche conformation<br />increases from compound 1 to compound 4. The NBO analysis of donor-acceptor interactions<br />showed that the generalized anomeric effect (GAE) is in favor of the gauche conformations of<br />compounds 1 and 2. Contrary to compounds 1 and 2, GAE is in favor of the anti conformations<br />of compounds 3 and 4. The GAE values calculated (i.e. GAEanti-GAEgauche) increase from<br />compound 1 to compound 4. On the other hand, the calculated dipole moment values for the<br />gauche conformations increase from compound 1 to compound 3 but decreases from compound<br />3 to compound 4. Based on the results obtained, there is no conflict between the GAE and the<br />electrostatic model impacts on the conformational preferences in compounds 1-3 but the<br />electrostatic model can not rationalize the increase of the instability of the gauche conformation<br />of compound 4 compared to its anti conformation on going from compound 3 to compound 4.<br />Consequently, in the conflict between the GAE and the electrostatic model, the former succeeded<br />in accounting for the increase of the anti conformation stability from compound 1 to compound<br />4. There is a direct correlation between the calculated GAE, Δ[rSi-Si(G)-rSi-Si(A)] parameters. The<br />correlations between the GAE, bond orders, ΔGAnti-Gauche, ΔG‡(Gauche→Gauche′, C2v),<br />ΔG‡(Anti→Gauche, C2), dipole-dipole interactions, structural parameters and conformational<br />behaviors of compounds 1-4 have been investigated.