above reaction is an example of Nucleophilic aromatic substitution. Which of the following halide (-X) is most readily replaced.

Options

A. `_F`
B. `-Cl`
C. `-Br`
D. `-I`

Answer

A

Explanation

Fluoride is the most reactive leaving group in nucleophilic aromatic substitution, iodide the least reactive.

Step 2: Elimination stage. Loss of halide from the cyclohexadienyl intermediate restores the aromaticity of the ring and gives the product of nucleophilic aromatic substitution.

Before leaving this mechanistic discussion, we should mention that the addition elimination mechanism for nucleophilic aromatic substitution illustrates a principle worth remembering. The words activating and deactivating as applied to substituent effects in organic chemistry are without meaning when they stand alone. When we say that group is activating or deactivating, we need to specify the reaction type that is being considered. A nitro group is a strongly deactivating substituent in electrophilic aromatic substitution, where it markedly destabilizes the key cyclohexadienyl cation intermediate.