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.