Hypervalent Sulfur Fluorides

The four equatorial fluorines of p-tolyl-SF4Cl appear as a singlet at +137.7 ppm. Since sulfur has a significant (4.3%) 34-isotope, there appears a small signal just upfield that is due to the isotope effect on the fluorine chemical shift of the S-34 component. 

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Hexacoordinate, hypervalent sulfur fluorides have an octahedral geometry that is symmetrical for SF6, which appears as a sharp singlet at +56 ppm, but which has magnetically nonequivalent (axial and equatorial, ab4 system) fluorines for compounds of the structure R-SF5. Compounds with the general structure R-SF4-X can exist as cis- and trans-isomers, the former having three types of fluorine, and the latter only one (Scheme 7.17). 

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