[IIT 1992] Nitrobenzene, treated with Br₂ in the presence of FeBr₃, gives *m*-bromonitrobenzene as the major product. Which of the following correctly explain(s) why the *meta* isomer predominates?
(A)The relative electron density on the *meta* ring carbon is higher than at *ortho*/*para*, since attack at *ortho*/*para* would place the developing positive charge of the arenium intermediate directly on (or adjacent to) the already electron-poor, nitro-bearing carbon, which is strongly destabilisingCorrect
(B)Loss of aromaticity when Br⁺ attacks the ring is, in effect, more easily "paid back" (i.e., the arenium intermediate is less destabilised) when attack occurs at the *meta* position rather than *ortho*/*para*Correct
(C)Nitrobenzene's ring is activated overall for electrophilic substitution
(D)*meta*-Substitution requires no arenium (Wheland) intermediate at all
Answer: (A),(B)
Solution
The strongly electron-withdrawing nitro group destabilises positive charge most severely when that charge falls on the carbon bearing (or directly adjacent to) the nitro group — which happens in the *ortho*/*para*-attack arenium ions but not in the *meta*-attack arenium ion. Both (A) and (B) describe this same
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