CBSE Class 12 Chemistry sample paper 2025-26: question 27

Hints

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Step-by-step solution

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1. I. ${\text{CH}}_3{\text{COCH}}_2{\text{CH}}_3\stackrel{{\text{C}}_2{\text{H}}_5\text{MgBr, dry ether}}{\to }({\text{C}}_2{\text{H}}_5{)}_2{\text{C(CH}}_3)\text{OMgBr}\stackrel{{\text{H}}_3{\text{O}}^{+}}{\to }({\text{C}}_2{\text{H}}_5{)}_2{\text{C(OH)CH}}_3$ (3-methylpentan-3-ol)

   1 mark

2. II. ${\text{C}}_6{\text{H}}_5{\text{OCH}}_3+{\text{CH}}_3\text{Cl}\stackrel{{\text{anhyd. AlCl}}_3}{\to }p{\text{-CH}}_3{\text{C}}_6{\text{H}}_4{\text{OCH}}_3$ (4-methoxytoluene, major) + some ortho isomer (Friedel–Crafts alkylation; –OCH${}_3$ is o/p directing).

   1 mark

3. III. ${\text{C}}_6{\text{H}}_5\text{OH}+\text{Zn}\stackrel{\Delta }{\to }{\text{C}}_6{\text{H}}_6+\text{ZnO}$ (distillation with zinc dust)

   1 mark

4. IV. Williamson synthesis: ${\text{C}}_2{\text{H}}_5\text{OH}+\text{Na}\to {\text{C}}_2{\text{H}}_5\text{ONa}$; then ${\text{C}}_2{\text{H}}_5\text{Cl}+{\text{C}}_2{\text{H}}_5\text{ONa}\to {\text{C}}_2{\text{H}}_5{\text{OC}}_2{\text{H}}_5+\text{NaCl}$ (alternatively, heat C${}_2$H${}_5$Cl with dry Ag${}_2$O).

Answer: I. Butan-2-one + C₂H₅MgBr, then H₃O⁺; II. CH₃Cl/anhyd. AlCl₃; III. Zn dust, heat; IV. C₂H₅ONa (Williamson synthesis). Any three carry 1 mark each.

Revise the chapter

• Chapter: Alcohols, Phenols and Ethers (notes, formulas, where marks are lost and every past question)
• Topic: Ethers: Williamson Synthesis and Cleavage