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

Hybrid-density functional theory (B3LYP/Def2-TZVPP) based method and NBOinterpretation were used to investigate the conformational behavior of 1,2-dihalodisilanes[halo=F (1), Cl (2), Br (3), I (4)]. The B3LYP/Def2-TZVPP results showed that the anticonformations of compounds 1-4 are more stable than their corresponding gaucheconformations. The stability of the anti conformation compared to the gauche conformationincreases from compound 1 to compound 4. The NBO analysis of donor-acceptor interactionsshowed that the generalized anomeric effect (GAE) is in favor of the gauche conformations ofcompounds 1 and 2. Contrary to compounds 1 and 2, GAE is in favor of the anti conformationsof compounds 3 and 4. The GAE values calculated (i.e. GAEanti-GAEgauche) increase fromcompound 1 to compound 4. On the other hand, the calculated dipole moment values for thegauche conformations increase from compound 1 to compound 3 but decreases from compound3 to compound 4. Based on the results obtained, there is no conflict between the GAE and theelectrostatic model impacts on the conformational preferences in compounds 1-3 but theelectrostatic model can not rationalize the increase of the instability of the gauche conformationof compound 4 compared to its anti conformation on going from compound 3 to compound 4.Consequently, in the conflict between the GAE and the electrostatic model, the former succeededin accounting for the increase of the anti conformation stability from compound 1 to compound4. There is a direct correlation between the calculated GAE, Δ[rSi-Si(G)-rSi-Si(A)] parameters. Thecorrelations between the GAE, bond orders, ΔGAnti-Gauche, ΔG‡(Gauche→Gauche′, C2v),ΔG‡(Anti→Gauche, C2), dipole-dipole interactions, structural parameters and conformationalbehaviors of compounds 1-4 have been investigated.