See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Reactivity with Concentrated HCl: Alcohol Substitution **Reaction Type:** These compounds undergo nucleophilic substitution with HCl to form alkyl chlorides. **Key Factor:** Reactivity depends on the **stability of the carbocation intermediate** formed during the $S_N1$ mechanism. ## Analysis of Each Option: **(A)** $C_6H_5-CH_2-CH_2-OH$ → Primary alcohol forms **primary carbocation** (unstable, least reactive) **(B)** $C_6H_5-CH(OH)-CH_3$ → Secondary alcohol forms **secondary benzylic carbocation** (highly stabilized by resonance with benzene ring) **(C)** $C_6H_5-OH$ → Phenol (aromatic $OH$) — does **not** undergo substitution readily due to $C-O$ bond aromaticity **(D)** $C_6H_5-CH_2-OH$ → Primary benzylic alcohol forms **primary carbocation** (less stable than secondary) ## Why B is Fastest: Option **(B)** forms a **secondary benzylic carbocation** that is stabilized by: - Resonance delocalization into the benzene ring - Hyperconjugation effects The benzylic stabilization makes this carbocation formation fastest, leading to rapid $S_N1$ substitution with HCl. **Answer: (B)**