See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Tautomerism Analysis **Tautomerism** requires structural isomers that can interconvert via migration of a hydrogen atom and a double bond (typically keto-enol tautomerism). ## Examining each option: **(1) Diketone (cyclohexanone derivative)** - Both carbonyls are in a saturated ring with bulky $tert$-butyl groups - No α-hydrogen available adjacent to carbonyl for enolization - **Cannot exhibit tautomerism** ✗ **(2) $CH_3-CH_2-N=\stackrel{O}{N}$ (N-nitrosoethylamine)** - Contains N=N-O structure with an α-hydrogen on the adjacent carbon - Can tautomerize: $CH_3-CH_2-N=N-O \rightleftharpoons CH_3-CH=N-NH-O$ - Forms a nitroso-amine tautomeric pair - **Exhibits tautomerism** ✓ **(3) 1,4-Benzoquinone** - Highly stable aromatic dione with conjugated system - No accessible α-hydrogens for tautomeric shift - Resonance stability prevents keto-enol conversion - **Cannot exhibit tautomerism** ✗ **(4) Benzaldehyde** - Aromatic aldehyde with aromatic ring directly attached - No α-hydrogen available (aromatic C-H is not labile) - Cannot form enol tautomer - **Cannot exhibit tautomerism** ✗ **Answer: (2)** exhibits tautomerism due to the presence of a labile α-hydrogen and the N=N-O functional group capable of proton-coupled double bond migration.