A Displacement of fluorine from saturated carbon - Sn2 processes

A Displacement of fluorine from saturated carbon - Sn2 processes 

Of course, the extreme of 5.13A would be complete bond formation with the nucleophile in an addition-elimination process, such as can occur when fluorine is bound to unsaturated carbon. Since a fluorine atom attached to carbon leads to a very polar, yet very strong, bond, we have two conflicting effects (a) the attached carbon is 

Fluoride ions (or incipient fluoride ions) form very strong hydrogen bonds, much stronger than corresponding bonds to chloride, and so a change to a more hydrogen- 

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