Schooling · Class 12 · Chemistry · Alcohols, Phenols and Ethers · Chapter on a page
CBSE Class 12 · Chemistry · NCERT Chemistry-II
Alcohols, Phenols and Ethers: chapter on a page
A cut of Shishya's notes for this chapter: the first paragraph of the introduction and the key ideas, formulas and facts, common mistakes and quick revision lists, word for word. Nothing is added or reworded; the worked examples are left out (they are on the chapter page).
About the notes: Written by Shishya's AI on 27 Sept 2026 from the chapter's title and class level, in Shishya's own words — not a copy or summary of the textbook. Read the official chapter for the book's own text, activities and exercises.
Fact-checked on 21 Oct 2026: an AI-assisted check of this note against cited sources; the errors it found were corrected that day. Some errors may remain.
Mind map
Drawn from the same notes by a fixed rule (no AI): each label is the item's own words — its bold term, its label before a colon, a short formula as written, or its first words.
The mind map as a list
- Key ideas
- Alcohols are classified as primary…
- Phenols are more acidic than…
- Hydrogen bonding between –OH groups…
- Alcohols undergo nucleophilic…
- Dehydration of alcohols with…
- Ethers are relatively inert but…
- The Williamson synthesis prepares…
- Formulas and facts
- General formula of alcohols
- Acidity order
- Lucas test
- Iodoform test
- Kolbe reaction
- Reimer–Tiemann reaction
- Williamson synthesis
- Worked examples
- IUPAC naming
- Predicting product of dehydration
- Williamson ether synthesis
- Watch out for
- Writing phenol as an alcohol because…
- Expecting ethers to react with…
- Applying Sₙ2 conditions to tertiary…
- Confusing the temperature conditions…
- Forgetting resonance stabilisation…
What this chapter is about
This chapter introduces three important families of organic compounds that contain oxygen bonded to carbon: alcohols, phenols and ethers. Alcohols have a hydroxyl group (–OH) attached to a saturated carbon atom; phenols have the –OH group bonded directly to a benzene ring; ethers have an oxygen atom bonded to two carbon groups. All three are widespread in daily life—ethanol in sanitisers, phenol in disinfectants, diethyl ether as an anaesthetic solvent.
Key ideas
- Alcohols are classified as primary (1°), secondary (2°) or tertiary (3°) depending on the number of carbon atoms attached to the carbon bearing the –OH group.
- Phenols are more acidic than alcohols because the phenoxide ion (C₆H₅O⁻) is stabilised by resonance with the benzene ring.
- Hydrogen bonding between –OH groups raises the boiling points of alcohols and phenols compared to ethers of similar molar mass.
- Alcohols undergo nucleophilic substitution: the –OH is replaced by halogen when treated with HX, PCl₃, PCl₅ or SOCl₂.
- Dehydration of alcohols with concentrated H₂SO₄ or Al₂O₃ at high temperature gives alkenes; the ease follows the order 3° > 2° > 1°.
- Ethers are relatively inert but undergo cleavage with concentrated HI or HBr to give alcohols and alkyl halides.
- The Williamson synthesis prepares ethers by reacting a sodium alkoxide with an alkyl halide through an Sₙ2 mechanism.
- Phenols show electrophilic aromatic substitution—bromination, nitration, Kolbe and Reimer–Tiemann reactions—due to the activating –OH group.
Formulas and facts to remember
- General formula of alcohols: CₙH₂ₙ₊₁OH (for saturated, mono-hydroxy alcohols).
- Acidity order: alcohols (pKₐ ≈ 16–18) < water (pKₐ ≈ 15.7) < phenol (pKₐ ≈ 10).
- Lucas test: tertiary alcohols react immediately with Lucas reagent (anhydrous ZnCl₂ + conc. HCl) giving a turbid layer; secondary alcohols react in 5–10 minutes; primary alcohols do not react at room temperature.
- Iodoform test: ethanol and any secondary alcohol with a CH₃–CHOH– unit give a yellow precipitate of CHI₃ when warmed with I₂ and NaOH.
- Kolbe reaction: phenol + NaOH → sodium phenoxide; then CO₂ at 400 K and 4–7 atm → sodium salicylate → salicylic acid on acidification.
- Reimer–Tiemann reaction: phenol + CHCl₃ + aqueous NaOH → salicylaldehyde (ortho-hydroxybenzaldehyde).
- Williamson synthesis: R–O⁻Na⁺ + R′–X → R–O–R′ + NaX (works best when R′–X is a primary halide to favour Sₙ2).
- Dehydration temperature guide: ethanol requires about 443 K with excess conc. H₂SO₄ to form ethene; at 413 K diethyl ether forms instead.
Common mistakes
- Writing phenol as an alcohol because both have –OH → Remember: in phenol the –OH is directly attached to the benzene ring, giving different acidity and reactions.
- Expecting ethers to react with dilute acids or bases as alcohols do → Ethers lack an acidic hydrogen and are largely unreactive except with strong halogen acids.
- Applying Sₙ2 conditions to tertiary substrates in Williamson synthesis → Tertiary halides favour elimination; always use a primary halide with the bulkier group as the alkoxide.
- Confusing the temperature conditions for alcohol dehydration → Lower temperature (around 413 K) favours ether formation; higher temperature (around 443 K) favours alkene.
- Forgetting resonance stabilisation when comparing acidity of phenol and alcohols → The phenoxide ion delocalises negative charge into the ring, making phenol about 10⁶ times more acidic than ethanol.
Quick revision
- Alcohols: –OH on saturated C; phenols: –OH on benzene; ethers: C–O–C linkage.
- Hydrogen bonding raises boiling points of alcohols and phenols above those of ethers.
- Phenol is acidic enough to dissolve in aqueous NaOH; alcohols are not.
- Lucas test distinguishes 1°, 2° and 3° alcohols by turbidity time.
- Williamson synthesis: alkoxide + primary alkyl halide → ether (Sₙ2 pathway).
- Concentrated HI cleaves ethers; the smaller alkyl group usually leaves as the iodide.