See image — Amines Chemistry Question

💡 Solution & Explanation

Step 1 - Identify the starting material: The starting material is 2-aminodiphenylmethane (2-benzylaniline), which has an NH2 group on a benzene ring at the ortho position relative to the CH2 group connecting two benzene rings. Step 2 - Reaction with NaNO2/H2SO4: This is a diazotization reaction. The primary aromatic amine (NH2) reacts with NaNO2 in the presence of H2SO4 to form a diazonium salt (ArN2+) at low temperature. Step 3 - Intramolecular cyclization: The diazonium salt formed is positioned ortho to the CH2 bridge connecting to the second benzene ring. The diazonium group can undergo intramolecular electrophilic aromatic substitution (or loss of N2 to form a carbocation/aryne, followed by cyclization) with the adjacent benzene ring. Since the NH2 is ortho to the CH2 group, the diazonium nitrogen is geometrically close to the second phenyl ring. Loss of N2 generates a highly reactive aryl cation (or the diazonium acts as electrophile) that attacks the neighboring benzene ring. Step 4 - Product formation: The intramolecular cyclization closes a five-membered ring between the two benzene rings via the CH2 bridge and the new C-C bond formed. This produces fluorene, a tricyclic compound with two benzene rings fused to a central cyclopentane (five-membered) ring. Step 5 - Why other options fail: - Option (a) would require formation of a six-membered central ring, but the CH2 bridge provides only one carbon, giving a five-membered ring upon cyclization. - Option (c) is anthracene-type with four rings, which is not consistent with the atom count. - Option (d) is naphthalene (two fused benzene rings) with no bridge carbon incorporated. The product with a five-membered central ring connecting the two benzene rings is fluorene, matching option (b). Therefore, the correct answer is B.