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Alcohols, Phenols & Ethers | Class 12 Organic Chemistry | SM-Educate

Alcohols, Phenols & Ethers | Class 12 Organic Chemistry | SM-Educate
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CS-991 · Module O-XII2

Alcohols, Phenols & Ethers

Class XII · Organic Chemistry
🎥 Video lesson coming soon

🍺 Alcohols (R-OH)

Preparation:

  • Hydration of alkenes (acid-catalysed addition of water)
  • Reduction of aldehydes/ketones (using NaBH₄ or LiAlH₄)
  • Reaction of a Grignard reagent with a carbonyl compound

Reactions: oxidation (to aldehydes/ketones/acids), esterification with carboxylic acids, and dehydration to alkenes.

⚖️ Phenols (Ar-OH)

Phenols are more acidic than ordinary alcohols because the negative charge on the phenoxide ion (formed after losing H⁺) is stabilized by resonance delocalization into the aromatic ring.

Phenols are commonly prepared industrially via the cumene process, or in the lab by hydrolysis of a diazonium salt.

The -OH group strongly activates the benzene ring, making phenols undergo electrophilic aromatic substitution much more readily than benzene itself.

🔗 Ethers & Williamson Synthesis

The Williamson Ether Synthesis is the standard method for preparing ethers:

R-O⁻ Na⁺ + R'-X → R-O-R' + NaX

An alkoxide ion (from an alcohol + Na or NaH) acts as a nucleophile and attacks an alkyl halide in an SN2 mechanism. It works best with a primary alkyl halide, since a bulkier secondary or tertiary halide favours elimination instead.

📝 Practice MCQs

Q1: Phenols are more acidic than alcohols because:
a) They contain more carbon atoms b) The phenoxide ion is resonance-stabilized c) They have a lower boiling point d) They are aromatic only
Show Answer
✅ b) The phenoxide ion is resonance-stabilized
Q2: The Williamson synthesis is used to prepare:
a) Alcohols b) Ethers c) Carboxylic acids d) Amines
Show Answer
✅ b) Ethers
Q3: The Williamson synthesis works best with which type of alkyl halide?
a) Primary b) Secondary c) Tertiary d) Aromatic
Show Answer
✅ a) Primary
Q4: Phenols undergo electrophilic aromatic substitution more readily than benzene because:
a) The -OH group deactivates the ring b) The -OH group activates the ring c) Phenols are not aromatic d) There is no effect
Show Answer
✅ b) The -OH group activates the ring
Q5: The Williamson synthesis mechanism is best described as:
a) SN1 b) SN2 c) E1 d) E2
Show Answer
✅ b) SN2
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