When the aromatic hydrocarbon naphthalene reacts with nitric and sulfuric acids, two compounds containing one nitro group are formed. What are the structures of these two compounds?
The two compounds are 1-nitronaphthalene and 2-nitronaphthalene.
The nitration of naphthalene is an electrophilic aromatic substitution.
It involves the attack of nitronium ion, NO₂⁺, on the aromatic system.
Attack at C-1
Nitration at C-1 produces a carbocation that has 7 resonance contributors.
Four of these ( 1, 2, 6, and 7) preserve the aromaticity (six π electrons) of the second ring.
Attack at C-2
Nitration at C-2 produces a carbocation that has 6 resonance contributors.
Two of these (1 and 6) preserve the aromaticity of the second ring.
So attack at C-1 is favoured, because it forms the most stable intermediate.
The major product is 1-nitronaphthalene. The minor product is 2-nitronaphthalene.