Structures of the Octahedral Persulfuranes H₄SF₂, H₂SF₄, Me₂SH₄ and Me₂SF₄, and Activation Enthalpies for Their cis/trans Isomerization

Abstract

Eight hypothetical persulfurane molecules of the type X 2 SY 4 (X, Y = H, F, Me) have been studied by ab initio MO calculations at the G3(MP2) level of theory. Depending on the substituents either the cis or the trans isomers of these octahedral molecules are most stable. While H 4 SF 2 is most stable as the cis isomer, the global minimum structures of H 2 SF 4 , Me 2 SH 4 , and Me 2 SF 4 are the trans isomers. The enthalpy differences between the corresponding isomers are in the range 7−53 kJ·mol −1 . The transition states for the intramolec-

Computational design of Oligo-sulfuranes

“…The sulfuranes we considered are shown in Figure 7, so chosen, as to match the symmetry of CH 2 and also to invoke electronegativity perturbation. Our qualitative arguments are difficult to support by quantitative diagrams or numbers because of several reasons: (1) Since there are lone pairs on F, which often mix with the radial orbital combinations, it is difficult to show a one-to-one relationship between the qualitative MO pictures and the computed MOs; (2) The sulfurane geometries considered are not the optimized geometries, they are constructed by the removal of adjacent H atoms from the corresponding persulfuranes, as indicated in Figure 7 (these persulfuranes were studied computationally by Steudel et al 26 ). This was necessary, as the structures 4 and 5 cannot be obtained as stationary points after optimization.…”