F2SO, F2SS, and CH3 2SO

If it is assumed that an oxygen lone-pair electron delocalizes into a sulphur 3d orbital for either molecule, Lewis structures (11) and (12) are obtained. The latter 

Each of the tetrahedral AX3Y molecules of this Section has 32 valence-shell electrons, as have the sulphones and AO4 anions of Sections 17-4 and 17-5. Consideration of the bonding for these AX3Y molecules provides some support for the hypothesis that fluorine atoms can stabilize Pauling 3-electron-bonds in 4-electron 3-centre bonding units for neutral molecules, and that Lewis structures with expanded valence-shells for sulphur atoms could be appropriate if the sulphur atoms acquire +2 formal charges in the Lewis octet structures. 

For F3NO, the standard Lewis structures are of types (13)-(15). The N-F and N-0 bond-lengths of 1.432 A and 1.159 A for this molecule are respectively longer than the N-F bonds of NFj (1.37 A) and similar to the bond-length 

For F3SN, the standard Lewis stractures are of types (21)-(23). These structures satisfy the Lewis-Langmuir octet rule, but each carries a formal charge of +2 on the sulphur atom. 

To help decide which set of delocalizations predominates, initially we shall give consideration to the bonding for FSN. For this molecnle, the S-N and S-F bond-lengths of 1.45 A and 1.65 A are respectively shorter than 1.50 A for free SN (with the Panling 3-electron bond structure (28)), 

---