Question

In the following compunds which one will go the fastest ArSN reaction .

According to me the fastest would be among compound (B) & (D) due to -M . But how to compare among these.

Answer 1

reactivity depends on stability of ring and carbocation.. -NH2 gives electrons to carbonation (if formed) will stabilize it, so it is more likely to be reactive. NO2 is Withdrawer so it increases charge on carbocation and destabilize it. +ive charge is inversely related to stability of carbocation....2nd thing this effect decreases with distance..