88. The number of distinct products formed after the nitration of tetralone in the presence of HNO₃ and H₂SO₄ is ________. (in integer)

Number of Distinct Products Formed After Nitration of Tetralone

Correct Answer

✅ Correct Answer: 4

Understanding the Structure of Tetralone

Tetralone (commonly 1-tetralone) consists of a benzene ring fused with a six-membered cyclohexanone ring. The carbonyl group is present in the saturated ring, while the benzene ring remains aromatic and undergoes electrophilic substitution during nitration.

Under nitrating conditions, nitric acid and sulfuric acid generate the electrophile, the nitronium ion (NO₂⁺), which attacks the aromatic ring. Since the reaction is an electrophilic aromatic substitution, nitration occurs only on the benzene ring and not on the saturated cyclohexanone ring.

Effect of the Carbonyl Group

The carbonyl group is an electron-withdrawing substituent that decreases the electron density of the fused aromatic system through its inductive effect. Although it influences the reactivity of the benzene ring, the aromatic ring still undergoes nitration under strongly acidic conditions.

Because of the fused bicyclic structure, the aromatic carbon atoms are not all equivalent. Careful examination of the symmetry of tetralone shows that four different aromatic positions are chemically distinguishable for mononitration.

Counting the Distinct Nitration Products

During electrophilic aromatic substitution, a nitro group may be introduced at each chemically unique aromatic carbon.

Analysis of the molecular symmetry of tetralone shows that:

• Equivalent positions generated by symmetry produce the same compound.
• Non-equivalent aromatic carbons give different constitutional isomers.
• The benzene ring contains four chemically distinct substitution sites.

Therefore, mononitration of tetralone produces a total of four distinct constitutional isomers.

Why the Answer is Four

Although the aromatic ring contains several carbon atoms, molecular symmetry reduces the number of unique substitution products. After accounting for equivalent positions created by the fused ring system, only four different nitro derivatives can be formed.

No additional products are counted because only one nitro group is introduced during mononitration.

Final Answer

Mononitration of tetralone using concentrated nitric acid and sulfuric acid produces four distinct constitutional isomers.

✅ Correct Answer: 4