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Fluoride ion works as a good leaving gro...

Fluoride ion works as a good leaving group in aromatic nucleophilic substitution of 2,4-dinitro fluorobenzene, even though it is a poor leaving group in aliphatic `S_(N)1andS_(N)2` mechanisms. Why?

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In aromatic nucleophilic substitution when the leaving group is Cl, Br or the rate differs only by a factor of 5. This behaviour is not expected in a reaction in which Ar X bond is broken in the rate determining step: An increase in the electronegativity of the leaving group such s F causes a decrease in the electron density at the ste of attack by the nucleophile, resulting in the last reaction When the leaving gras the rate is much faster compared to other to groups. This indicates that the mechanism is different from `S_(N)1andS_(N)2` path ways.
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