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:

  1. 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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