Pair and Bond Charge Models for Fluorohydrocarbons

Lone Pair and Bond Charge Models for Fluorohydrocarbons 

Since fluorine is more electronegative than nitrogen, it might be anticipated that lone pair effects on the electric potential would be larger at F than at N. A PD study of fluorohydrocarbons by Williams and Houpt does not support this anticipation. Table 11 shows PD models for three fluorohydrocarbons. 

Note that the fit of the AC model for hexafluorobenzene (11.0%) is better than the AC model for s-tetrazine (16.6%, Table 8), and also that the improvement in fit given by the LP model is less in hexafluorobenzene (4.3%) than in s-tetrazine (1.6%). So, contrary to expectation based on the larger electronegativity of fluorine, lone-pair effects as modeled here are less important in hexafluorobenzene than in s-tetrazine. In fact. Table 11 shows that a better fit to the electric potential of these fluorocarbons can be obtained by placing sites at the centers of the C—F bonds. 

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Table 11 Potential-Derived Lone-Pair and Bond-Charge Models for Fluorohydrocarbons...

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