See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

# Analysis of Tautomerism in Each Compound **Tautomerism** requires a mobile hydrogen atom adjacent to an unsaturated group (typically $C=O$ or $C=N$), allowing keto-enol or similar equilibria. ## Checking Each Option: **(A) $CH_3NO_2$ (Nitromethane)** - Contains $N=O$ groups with an adjacent $CH_3$ group - The $\alpha$-hydrogen is acidic and can migrate to oxygen - **Exhibits tautomerism** ✓ **(B) $CH_3CH_2NO_2$ (Nitroethane)** - Contains $N=O$ groups with $\alpha$-hydrogens on the ethyl chain - Acidic hydrogens can tautomerize similarly to nitromethane - **Exhibits tautomerism** ✓ **(C) $C_6H_5CH=CH-OH$ (Cinnamyl alcohol)** - Contains an $OH$ group attached directly to a $C=C$ double bond (enol form) - This is already an **enol**, not a ketone - No acidic hydrogen adjacent to $C=O$ for keto-enol tautomerism - The $OH$ cannot migrate to form a more stable tautomer - **Does NOT exhibit tautomerism** ✗ **(D) $CH_3CH_2OH$ (Ethanol)** - Simple alcohol with no unsaturated groups nearby - No tautomerism possible - But this is trivially obvious ## Answer: **(C)** is correct because it's already an enol form with no carbonyl group present, so no tautomeric equilibrium can be established. The structural rearrangement that would constitute tautomerism cannot occur.