See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

# Tautomerism Analysis **Tautomerism** is the equilibrium between two readily interconvertible structural isomers that differ in the position of a hydrogen atom and a double bond. ## Evaluating Each Option: **(A) Phenylvinyl alcohol** ($C_6H_5-CH=CH-OH$) - Can undergo keto-enol tautomerism - The OH group can shift: $C_6H_5-CH=CH-OH \rightleftharpoons C_6H_5-CH_2-CHO$ - **Exhibits tautomerism** ✗ **(B) p-Benzoquinone** ($O=\underset{\text{para}}{\phantom{A}}-=O$) - This is an aromatic quinone (fully conjugated cyclic diketo compound) - Cannot undergo simple keto-enol tautomerism - The structure is stabilized by aromatic character; any proton migration would break aromaticity - **Does NOT exhibit tautomerism** ✓ **(C) Benzaldehyde** ($C_6H_5-CHO$) - Can undergo keto-enol tautomerism: $$C_6H_5-CHO \rightleftharpoons C_6H_5-CH=OH$$ - The aldehyde H can shift to the aromatic ring - **Exhibits tautomerism** ✗ **(D) Salicylic acid derivative** (HO-phenol with COOH) - Can show keto-enol tautomerism between the carboxylic acid and phenolic forms - **Exhibits tautomerism** ✗ ## Answer: **Options B and C do NOT exhibit tautomerism** because p-benzoquinone is too stable (aromatic stabilization prevents H migration), and benzaldehyde represents a limit case where the enol form is extremely unstable.