Question

Which of the following is easily nitrated using a mixture of \(HNO_3\) and \(H_2SO_4\) :

• A. Toluene
• B. Fluorobenzene
• C. Chlorobenzene
• D. Nitrobenzene

Answer 1

The Correct Option is A

The correct option is (A): Toluene.

Answer 2

Electrophilic aromatic nitration with a HNO3/H2SO4 mixture proceeds fastest on rings that are activated (electron-rich), and is slowed down on rings bearing electron-withdrawing or strongly deactivating substituents. Each option can be judged by the electronic effect of its substituent:

1. Toluene: The methyl group on toluene is an electron-donating group that increases the electron density of the benzene ring through hyperconjugation, activating the ring toward electrophilic attack and directing the incoming nitro group to the ortho and para positions. This makes toluene react faster than benzene itself in nitration.
2. Fluorobenzene: Fluorine is an ortho/para director through resonance donation of a lone pair, but it is strongly electronegative and withdraws electron density inductively, so on balance fluorobenzene is less reactive than benzene toward electrophilic substitution, not more.
3. Chlorobenzene: Like fluorine, chlorine directs ortho/para but is inductively electron-withdrawing overall, making the ring less activated than benzene and slower to nitrate than toluene.
4. Nitrobenzene: The nitro group is a powerful electron-withdrawing, meta-directing group that strongly deactivates the ring, making nitrobenzene considerably harder to nitrate further, requiring more forcing conditions than the other substrates listed.

Since an electron-donating alkyl substituent activates the ring while halogens and especially a nitro group deactivate it to varying degrees, the ring bearing the methyl group nitrates most readily.

Therefore, the correct answer is Toluene.