Question

In this $S_{N}Ar$ i.e. Substitution Nucleophilic aromatic reaction, which Fluorine has the highest tendency to get subsituted by the incoming nuclephile?

• A. Fluorine 1
• B. Fluorine 2
• C. Both have equal tendency.
• D. Cannot predict.

Answer 1

The correct option is A Fluorine 1

The negative charge of the intermediate formed when fluorine 1 is substituted by ${}^{-}OC{H}_3$ is stabilised by $–M$ effect of $–N{O}_2$ as shown:

Fluorine 2 is present at meta posiiton w.r.t $-N{O}_2$ group
$-M$ effect of $-N{O}_2$ stabilizes the negative charge only at ortho and para positions. So intermediate formed in case of substitution of fluorine 2 is not stabilized and hence less stable than the intermediate formed by replacing Fluorine 1
So, Fluorine 1 has higher tendency to get replaced by incoming nucleophile ${}^{-}OC{H}_3$