Can acyclic conformational control be achieved via a sulfur-fluorine gauche effect?

The gauche conformation of the 1,2-difluoroethane motif is known to involve stabilising hyperconjugative interactions between donor (bonding, sigma(C-H)) and acceptor (antibonding, sigma*(C-F)) orbitals. This model rationalises the generic conformational preference of F-C-beta-C-alpha-X systems (phi(FCCX) approximate to 60 degrees), where X is an electron deficient substituent containing a Period 2 atom. Little is known about the corresponding Period 3 systems, such as sulfur and phosphorus, where multiple oxidation states are possible. Conformational analyses of beta-fluorosulfides, -sulfoxides and -sulfones are disclosed here, thus extending the scope of the fluorine gauche effect to the 3rd Period (F-C-C-S(O)(n); phi(FCCS) approximate to 60 degrees). Synergy between experiment and computation has revealed that the gauche effect is only pronounced in structures bearing an electropositive vicinal sulfur atom (S+-O-, SO2).