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CBSE Class 12 Chemistry★ 7-9 marks · CBSE Class 12 Chemistry Chapter 7; acidity of phenols and named reactions feature in JEE and NEET

Alcohols, Phenols, and Ethers

ALCOHOLS (R−OH), PHENOLS (Ar−OH), and ETHERS (R−O−R') are oxygen-containing organic compounds with VAST importance in chemistry, biology, and industry. CBSE Class 12 Chemistry Chapter 7.

⏱ 22 min readMedium difficulty✓ Free · NCERT-aligned

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By the end of this chapter you'll be able to…

1Classify and name alcohols, phenols, and ethers
2Describe preparation routes including Grignard and Williamson's synthesis
3Distinguish 1/2/3 degree alcohols using the Lucas test and oxidation
4Explain why phenols are more acidic than alcohols
5Describe Kolbe's, Reimer-Tiemann reactions and ether cleavage by HI

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Why this chapter matters

Alcohols, phenols, and ethers are fundamental oxygen-containing compounds central to medicine, industry, and the chemistry lab. Their preparation, the contrasting acidity of alcohols and phenols, and named reactions like Kolbe's and Williamson's synthesis are core organic chemistry.

Before you start — revise these

A 5-minute refresher here will save you 30 minutes of confusion below.

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Class 12 Chemistry: Haloalkanes and Haloarenes

Substitution reactions and Grignard reagents

Alcohols, Phenols, and Ethers

'The −OH group is the most VERSATILE functional group in organic chemistry — it can act as both an acid and a base depending on the context.'

1. Chapter Overview

This chapter covers three related classes of oxygen-containing organic compounds: ALCOHOLS (hydroxyl group attached to an sp³ carbon), PHENOLS (hydroxyl group attached to an AROMATIC ring), and ETHERS (an oxygen atom bonded to TWO alkyl or aryl groups). Topics include: CLASSIFICATION and NOMENCLATURE, METHODS OF PREPARATION, PHYSICAL PROPERTIES (boiling point, solubility, acidity), and CHEMICAL REACTIONS of each class — including reactions of the −OH group, reactions of the aromatic ring in phenols, and the cleavage of ethers.

2. Alcohols

Classification

Monohydric: One −OH group. Dihydric (glycols) : Two −OH. Trihydric (glycerol) : Three −OH.
1°, 2°, 3°: Based on the carbon bearing the −OH group.

Preparation Methods

From alkenes: Hydration (acid-catalysed, Markovnikov). Hydroboration-oxidation (ANTI-Markovnikov).
From carbonyl compounds: Reduction of aldehydes → 1° alcohols. Ketones → 2° alcohols. Using NaBH₄ or LiAlH₄.
From Grignard reagents: RMgX + R'CHO → R'CH(OH)R (with aldehyde). RMgX + R'COR'' → R'R''C(OH)R (with ketone). RMgX + HCHO → RCH₂OH (with formaldehyde).

Physical Properties

Boiling points: MUCH HIGHER than corresponding alkanes (due to HYDROGEN BONDING).
Solubility: Lower alcohols (methanol, ethanol) are MISCIBLE with water. Solubility DECREASES as carbon chain increases.
Comparison: bp order: 1° > 2° > 3° (for isomeric alcohols).

3. Chemical Reactions of Alcohols

Reactions Involving O−H Bond (Acidity)

ROH + Na → RONa + ½H₂. 'Alcohols react with SODIUM metal to form alkoxides — proving that the O−H bond is WEAKLY acidic.'
Acidity: CH₃OH > 1° > 2° > 3° (due to electron-releasing alkyl groups stabilising the alkoxide ion).

Reactions Involving C−O Bond (Cleavage)

ROH + HX → RX + H₂O. Reactivity: HI > HBr > HCl (ZnCl₂ needed for HCl).
Lucas test: Distinguishes 1°, 2°, 3° alcohols using ZnCl₂/HCl. 3° → IMMEDIATE turbidity. 2° → turbidity in 5 min. 1° → NO turbidity at room temp.

Oxidation of Alcohols

1° alcohol → Aldehyde → Carboxylic acid (using K₂Cr₂O₇/H⁺, KMnO₄, PCC).
2° alcohol → Ketone (using K₂Cr₂O₇/H⁺).
3° alcohol → RESIST oxidation (no α-hydrogen).

Dehydration

ROH → Alkene + H₂O (using conc. H₂SO₄, Al₂O₃, or H₃PO₄).
Saytzeff rule: The MORE substituted alkene is the major product.
Ease of dehydration: 3° > 2° > 1°.

4. Phenols

Preparation

From chlorobenzene (Dow process) : C₆H₅Cl + NaOH (high P, T) → C₆H₅ONa → C₆H₅OH.
From cumene: C₆H₅CH(CH₃)₂ + O₂ → C₆H₅OH + CH₃COCH₃ (phenol + acetone).
From diazonium salts: C₆H₅N₂⁺ + H₂O → C₆H₅OH + N₂.

Acidity

Phenols are MORE acidic than alcohols (pKa ≈ 10 vs. pKa ≈ 16 for alcohols).
'The phenoxide ion is STABILISED by resonance with the aromatic ring — the charge is DELOCALISED.'
Effect of substituents: ELECTRON-WITHDRAWING groups (NO₂, Cl) INCREASE acidity. ELECTRON-RELEASING groups (CH₃) DECREASE acidity.
Picric acid (2,4,6-trinitrophenol) is a STRONG ACID (pKa ≈ 0.3).

Reactions

Esterification: C₆H₅OH + RCOCl → C₆H₅OCOR + HCl.
Electrophilic substitution (activating effect of −OH) : Bromination (2,4,6-tribromophenol — WHITE precipitate), Nitration, Friedel-Crafts.
Kolbe's reaction: CO₂ + C₆H₅ONa → salicylic acid (precursor of aspirin).
Reimer-Tiemann reaction: CHCl₃ + C₆H₅OH + NaOH → salicylaldehyde.

5. Ethers

Preparation

Williamson's synthesis: RONa + R'X → ROR' + NaX. 'The BEST method for preparing ethers — both symmetrical and unsymmetrical.'
- Use PRIMARY alkyl halide (to avoid elimination).
- For aryl ethers: C₆H₅ONa + R−X → C₆H₅OR + NaX.
Dehydration of alcohols: 2ROH → ROR + H₂O (conc. H₂SO₄, 140°C). 'At 140°C, ether forms. At 170°C, alkene forms.'

Physical Properties

'Ethers have NO hydrogen bonding capabilities (no −OH) — so their boiling points are LOWER than alcohols but higher than alkanes.'
ETHERS are SLIGHTLY SOLUBLE in water (can form H-bonds with water via the oxygen).
Diethyl ether: bp 35°C — highly VOLATILE and FLAMMABLE.

Chemical Reactions

Cleavage by acids: ROR' + HI → ROH + RI (first) → 2RI + H₂O (second, with excess HI).
'When unsymmetrical ether is cleaved by HI, the SMALLER alkyl group forms the alkyl iodide.'
Autoxidation: Ethers form EXPLOSIVE peroxides when exposed to air and light.

6. Comparison Table: Acidity

Compound	pKa	Explanation
Water	15.7	Reference
Ethanol	16	Alkyl group stabilises ethoxide — LESS acidic than water
Phenol	10	Resonance stabilises phenoxide — MORE acidic than water and alcohols
Acetic acid	4.76	Carboxylate ion resonance — STRONGER acid than phenol

7. Common Mistakes

Lucas test confusion: Tertiary alcohols react INSTANTLY — it is NOT about the TIME but the RAPIDITY of turbidity.
Williamson's synthesis: Always use the ALKOXIDE of the LESS hindered alcohol and the alkyl HALIDE of the MORE hindered group. Using a tertiary alkyl halide leads to ELIMINATION, not substitution.
Oxidation of primary alcohols: The product DEPENDS on the oxidising agent. With PCC: aldehyde stops. With K₂Cr₂O₇/H⁺: goes to carboxylic acid.
Phenol is NOT an alcohol: The −OH group is DIRECTLY attached to the aromatic ring. The properties are DISTINCT — phenol is acidic, alcohol is not significantly acidic.

8. CBSE Exam Focus

Classification and IUPAC naming of alcohols, phenols, and ethers
Preparation of alcohols — from alkenes (hydration, hydroboration), carbonyl compounds, Grignard
Distinction between 1°, 2°, 3° alcohols (Lucas test, oxidation)
Acidity of phenols — comparison with alcohols, effect of substituents
Kolbe's and Reimer-Tiemann reactions of phenol
Williamson's synthesis of ethers
Cleavage of ethers by HI

9. Self-Test

Q1: Distinguish between ethanol and phenol using a chemical test. A1: Add neutral FeCl₃ solution. Phenol gives a VIOLET colour (due to [Fe(OC₆H₅)₆]³⁻). Ethanol gives NO colour.

Q2: What is the product when phenol is treated with excess bromine water? A2: 2,4,6-Tribromophenol (WHITE precipitate). This is a TEST for phenol.

Q3: Arrange in decreasing order of acidity: Water, Ethanol, Phenol, p-Nitrophenol. A3: p-Nitrophenol > Phenol > Water > Ethanol. (Electron-withdrawing NO₂ increases acidity. Phenoxide is resonance-stabilised. Ethoxide is NOT stabilised by resonance.)

Q4: Write the product when anisole (CH₃OC₆H₅) is treated with HI. A4: C₆H₅OH (phenol) + CH₃I (methyl iodide). 'The methyl group, being SMALLER, forms the alkyl iodide.'

Q5: Complete and name the reaction: C₆H₅ONa + CO₂ (followed by H⁺) → ? A5: Kolbe's reaction. Product: Salicylic acid (2-hydroxybenzoic acid). Used in the synthesis of ASPIRIN.

10. Conclusion

Alcohols, phenols, and ethers are FUNDAMENTAL oxygen compounds:

ALCOHOLS: 'Versatile — can be oxidised, dehydrated, substituted. They are the STARTING POINT for many organic syntheses.'
PHENOLS: 'Acidic (unlike alcohols). Undergo electrophilic substitution READILY. The foundation of antiseptics and pharmaceuticals.'
ETHERS: 'Excellent solvents (inert, dissolve many organics). Williamson's synthesis is the GO-TO method for making them.'
'From the ethanol in sanitiser to the phenol in antiseptic to the ether in the chemistry lab — these compounds are EVERYWHERE in daily life.'

Key formulas & results

Everything you need to memorise, in one card. Screenshot this for revision.

Acidity order

Carboxylic acid > phenol > water > alcohol

Phenoxide is resonance-stabilised; alkoxide is not.

Williamson's synthesis

RONa + R'X -> ROR' + NaX

Use a primary alkyl halide to avoid elimination.

Ether cleavage by HI

ROR' + HI -> ROH + R'I (smaller group forms the iodide)

Excess HI converts both parts to iodides.

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Common mistakes & fixes

These are the exact errors that cost students marks in board exams. Read them once, save yourself the trouble.

WATCH OUT

✗ Reading the Lucas test by time alone

✓ It is the rapidity of turbidity that matters: tertiary alcohols turn cloudy immediately, secondary in minutes, primary not at room temperature.

WATCH OUT

✗ Using a tertiary halide in Williamson's synthesis

✓ Tertiary alkyl halides give elimination; use the alkoxide of the more hindered alcohol with a primary halide.

WATCH OUT

✗ Assuming primary alcohol oxidation always gives an acid

✓ PCC stops at the aldehyde, while K2Cr2O7/H+ oxidises further to the carboxylic acid.

WATCH OUT

✗ Treating phenol as just another alcohol

✓ Phenol's -OH is attached to an aromatic ring, making it acidic and reactive in electrophilic substitution, unlike alcohols.

NCERT exercises (with solutions)

Every NCERT exercise from this chapter — what it covers and how many questions to expect.

Alcohols

Preparation, Lucas test, oxidation, dehydration

Questions

Phenols

Acidity, Kolbe's and Reimer-Tiemann reactions

Questions

Ethers

Williamson's synthesis and HI cleavage

Questions

Practice problems

Try each one yourself before tapping "Show solution". Active recall > rereading.

Q1EASY· Distinction

Distinguish between ethanol and phenol using a chemical test.

▶ Show solution

Add neutral FeCl3: phenol gives a violet colour, while ethanol gives no colouration.

Q2EASY· Reaction

What is the product when phenol reacts with excess bromine water?

▶ Show solution

2,4,6-tribromophenol, formed as a white precipitate -- a test for phenol.

Q3MEDIUM· Acidity

Arrange in decreasing order of acidity: water, ethanol, phenol, p-nitrophenol.

▶ Show solution

p-nitrophenol > phenol > water > ethanol. The electron-withdrawing nitro group increases acidity; phenoxide is resonance-stabilised; ethoxide is not.

Q4MEDIUM· Ethers

Write the product when anisole (CH3OC6H5) reacts with HI.

▶ Show solution

Phenol (C6H5OH) and methyl iodide (CH3I); the smaller methyl group forms the alkyl iodide.

Q5MEDIUM· Named Reaction

Name and complete: C6H5ONa + CO2 followed by H+ gives what?

▶ Show solution

Kolbe's reaction, giving salicylic acid (2-hydroxybenzoic acid), a precursor of aspirin.

5-minute revision

The whole chapter, distilled. Read this the night before the exam.

•Alcohols classified as mono/di/tri-hydric and 1/2/3 degree.
•Prepare alcohols from alkenes, carbonyls (NaBH4/LiAlH4), and Grignard reagents.
•Acidity: CH3OH > 1 > 2 > 3 degree alcohols; alcohols react with Na to give alkoxides.
•Lucas test distinguishes 1/2/3 degree alcohols; oxidation gives aldehyde/ketone/acid.
•Phenols are more acidic than alcohols (resonance-stabilised phenoxide).
•Kolbe's reaction gives salicylic acid; Reimer-Tiemann gives salicylaldehyde.
•Williamson's synthesis (RONa + R'X) is the best ether preparation; HI cleaves ethers.

CBSE marks blueprint

Where the marks come from in this chapter — so you can plan your prep.

Typical chapter weightage: 7-9 marks across the chapter

Question type	Marks each	Typical count	What it tests
Phenol acidity / reactions	3-5	1	Acidity comparison and named reactions
Alcohol preparation/reactions	3	1	Lucas test, oxidation, dehydration
Ethers	2-3	1	Williamson's synthesis and HI cleavage

Prep strategy

Compare acidity with reasons (resonance, substituents)
Learn the Lucas test and oxidation products
Memorise Kolbe's and Reimer-Tiemann reactions
Master Williamson's synthesis and ether cleavage

Where this shows up in the real world

This chapter isn't just an exam topic — it lives in the world around you.

Antiseptics and drugs

Phenol-based compounds are antiseptics, and salicylic acid is the basis of aspirin.

Solvents and fuels

Ethanol is a fuel and solvent; ethers are common laboratory solvents.

Industrial chemicals

Alcohols and phenols are feedstocks for plastics, resins, and many fine chemicals.

Exam strategy

Battle-tested tips from teachers and toppers for this chapter.

Justify acidity order with resonance and substituent effects
State reagents and conditions for each preparation
Recall named reactions (Kolbe, Reimer-Tiemann, Williamson)
Use distinguishing tests (FeCl3, bromine water) accurately

Going beyond the textbook

For olympiad aspirants and curious learners — topics that build on this chapter.

Analyse the mechanism and selectivity of ether cleavage by HI.
Compare acidity of substituted phenols quantitatively using Hammett constants.

Where else this chapter is tested

CBSE board isn't the only one — other exams test this chapter too.

CBSE Class 12 Chemistry examHigh

JEE Main and Advanced (Alcohols/Phenols/Ethers)High

NEET ChemistryMedium

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Questions students ask

The real ones — pulled from the Q&A community and tutor sessions.

When phenol loses its proton, the resulting phenoxide ion is stabilised by resonance: the negative charge is delocalised into the aromatic ring over several positions. This makes the phenoxide relatively stable, so phenol readily donates its proton (pKa about 10). In ethanol, the ethoxide ion has no resonance stabilisation -- the negative charge stays on the oxygen and is even destabilised by the electron-releasing alkyl group -- so ethanol is a much weaker acid (pKa about 16).

Williamson's synthesis is an SN2 reaction between an alkoxide and an alkyl halide. SN2 works best with primary halides, where there is little steric hindrance. If a secondary or tertiary halide is used, the strongly basic alkoxide instead causes elimination, giving an alkene rather than the ether. So to make an unsymmetrical ether, you pair the alkoxide of the more hindered group with a primary alkyl halide of the less hindered group, ensuring substitution dominates over elimination.

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