Question 1

Why is concentrated sulfuric acid used during nitration of benzene?

Accepted Answer

Concentrated sulfuric acid helps generate the nitronium ion, NO₂⁺, from concentrated nitric acid. This nitronium ion is the electrophile that attacks the benzene ring.

Question 2

What is the actual structure of the nitro group in nitrobenzene?

Accepted Answer

It is a resonance hybrid with two equivalent N–O bonds and a planar, sp²-hybridised nitrogen. Formal contributors can be drawn with N⁺ and one O⁻, but these are not separate structures rapidly switching between one another.

Question 3

Why is a nitro group meta-directing?

Accepted Answer

The nitro group withdraws electron density from the ring through the –I inductive effect and –M resonance effect. It therefore strongly deactivates the ring and makes meta attack the major pathway. Ortho and para attack can still occur under suitable conditions.

Question 4

How is nitrobenzene converted into aniline?

Accepted Answer

Nitrobenzene is reduced with Sn/HCl, Fe/HCl, or H₂ in the presence of Ni. With Sn/HCl or Fe/HCl, the product is initially protonated, so alkaline work-up is required to obtain free aniline.

Question 5

How does nitration change the benzene ring?

Accepted Answer

The π electrons of benzene attack NO₂⁺ to form an arenium σ-complex. Loss of H⁺ restores aromaticity and produces nitrobenzene, C₆H₅NO₂, with water as the coproduct.

Nitro Compounds: A Group That Withdraws

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