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COMEDK2024Evening ShiftChemistryAlcohols Phenols and EthersActual

Which one of the following is the correct order of reagents to be used to convent [A] to [X] ? Reagents: PCC , PCl ₅, LiAlH ₄, KCN H ₃ O ⁺

Options

  1. APCC PCl ₅ K C N H ₃ O ⁺ LiAlH ₄
  2. BK C N H₃ O ⁺ PCl ₅ PCC LiAlH ₄
  3. CLiAlH ₄, K C N H₃ O ⁺ PCl ₅ PCC
  4. DPCl ₅, K C N H₃ O ⁺ LiAlH ₄ PCC

Correct answer

D. PCl ₅, K C N H₃ O ⁺ LiAlH ₄ PCC

Step-by-step solution

The goal is to convert R-CH₂-OH to R-CH₂-CHO (adding one carbon via chain extension). PCl₅ : Converts alcohol to alkyl chloride (good leaving group). R-CH₂-OH PCl₅ R-CH₂-Cl KCN : Nucleophilic substitution adds cyanide, extending the chain by one carbon. R-CH₂-Cl KCN R-CH₂-CN H₃O^+ : Acidic hydrolysis converts nitrile to carboxylic acid. R-CH₂-CN H₃O^+ R-CH₂-COOH LiAlH₄ : Reduces carboxylic acid to primary alcohol. R-CH₂-COOH LiAlH₄ R-CH₂-CH₂-OH PCC : Selectively oxidises primary alcohol to aldehyde (stops at aldehy

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