See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

# Tautomerism Analysis **Definition:** Tautomerism is dynamic isomerism involving rapid interconversion between two forms (usually keto-enol equilibrium) differing in position of a hydrogen atom and a double bond. **Key Requirement:** A compound must have an **α-hydrogen** (hydrogen on carbon adjacent to a carbonyl or similar electron-withdrawing group) to exhibit tautomerism. **Evaluation of each option:** **(A) Chloroethane** ($CH_3CH_2Cl$) - No carbonyl group; no electron-withdrawing group adjacent to a C-H bond - Cannot form tautomers ✗ **(B) Ethanol** ($CH_3CH_2OH$) - Contains an $OH$ group (electron-withdrawing) - Exhibits **keto-enol tautomerism:** $$CH_3CH_2OH \rightleftharpoons CH_2=CH_2 + H_2O \text{ (or internal form)}$$ - More accurately: $CH_3-\overset{H}{C}-OH \rightleftharpoons CH_2=CH-OH$ (enol form) - Shows tautomerism ✓ **(C) Ethoxyethane** ($CH_3OCH_2CH_3$) - No carbonyl or acidic group - Cannot exhibit tautomerism ✗ **(D) Nitroethane** ($CH_3CH_2NO_2$) - While $NO_2$ is electron-withdrawing, the compound doesn't readily show the typical keto-enol tautomerism under normal conditions ✗ **Answer: (B) Ethanol** exhibits tautomerism due to the acidic hydrogen on the $OH$ group allowing equilibrium between the alcohol and enol forms.