See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

# Solution: HCN and HNC Isomerism **Step 1: Identify the structures** - $HCN$: $H-C\equiv N$ (hydrogen cyanide) - $HNC$: $H-N\equiv C$ (isocyanide/hydrogen isocyanide) **Step 2: Check molecular formula** Both have the same molecular formula: $C_1H_1N_1$ ✓ **Step 3: Analyze the type of isomerism** - **Functional isomerism** (A): Requires different functional groups. Here, both contain C≡N bonds with hydrogen attached — not different functional groups. - **Tautomerism** (B): A special type of structural isomerism involving **rapid interconversion** between two isomers through migration of a hydrogen atom (or proton) and a double bond, occurring in dynamic equilibrium. **Step 4: Verify tautomerism criteria** $$HCN \rightleftharpoons HNC$$ This conversion involves: - Migration of H between C and N atoms - Shift of electron density (π electrons) - Dynamic equilibrium between two forms - Same molecular formula maintained These are characteristic features of **tautomerism**. **Answer: (B) tautomerism** HCN and HNC represent keto-enol type tautomerism, where hydrogen rapidly oscillates between the two more electronegative atoms.