Theoretical Evidence for the Relevance of n(F) → σ*(C-X) (X = H, C, O, S) Stereoelectronic Interactions.

Theoretical calculations on r-1,c-3,c-5-trifluorocyclohexane (1), r-2,c-4,c-6-trifluoro-1,3,5-trioxane (2), and r-2,c-4,c-6-trifluoro-1,3,5-trithiane (3) confirm the importance of n(F) → σ*(C-Y)gem, where Y = H, C, O, S, hyperconjugative interactions; that is, contrary to common wisdom, fluorine is a good lone pair electron donor toward geminal sigma bonds. This conclusion is in line with the recent observations reported by O'Hagan and co-workers, who synthesized and examined all-cis 1,2,3,4,5,6-hexafluoro-cyclohexane (Nat. Chem. 2015, 7, 483-488).