Aromatic Compounds Containing Nitrogen - Result Question 32
33. When nitrobenzene is treated with $Br _2$ in the presence of $FeBr _3$, the major product formed is $m$-bromonitrobenzene. Statements which are related to obtain the $m$-isomer, are
$(1992,1 M)$
(a) the electron density on meta carbon is more than that on ortho and para positions
(b) the intermediate carbonium ion formed after initial attack of $Br^{+}$at the meta position is less destabilised
(c) loss of aromaticity when $Br^{+}$attacks at the ortho and para positions and not at meta position
(d) easier loss of $H^{+}$to regain aromaticity from meta position than from ortho and para positions
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Answer:
Correct Answer: 33. (a,b)
Solution:
- Nitro group withdraws electrons more from ortho/para position than from meta position. Also the $\sigma$-complex formed from meta attack is less destabilised than from ortho/para positions.
Nitro group not destabilising the positive charge by resonance.
Nitro group destabilises the positive charge directly by resonance, less stable $\sigma$-complex.
Similar phenomenon is observed with ortho attack.
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