Class 12 Chemistry – Chapter 11 Alcohols Phenols and Ether Notes
1. Classification
(A) Alcohols (R–OH)
Based on the carbon attached to –OH group:
Primary (1°) → R–CH₂–OH
Secondary (2°) → R₂CH–OH
Tertiary (3°) → R₃C–OH
(B) Phenols
–OH group directly attached to benzene ring
Example: C₆H₅OH
(C) Ethers (R–O–R′)
Symmetrical ether → R–O–R
Unsymmetrical ether → R–O–R′
2. Nomenclature (IUPAC)
Alcohols
Longest carbon chain containing –OH
–OH gets lowest possible number
Suffix: –ol
📌 Example:
CH₃–CH(OH)–CH₃ → Propan-2-ol
Phenols
–OH at position 1 of benzene
Substituents numbered accordingly
Ethers
Named as alkoxy alkanes
Smaller group → alkoxy (–OR)
📌 Example:
CH₃–O–C₂H₅ → Methoxyethane
3. Structure of Functional Groups
Alcohol / Phenol → –OH (polar)
Ether → –O– (less polar than alcohol)
4. Alcohols and Phenols – Physical Properties
Hydrogen Bonding
Alcohols & phenols form intermolecular H-bonding
Leads to:
Higher boiling point
Higher solubility in water (lower members)
📌 Ethanol > Ether (no H-bonding)
5. Chemical Properties of Alcohols
(A) Reactions with HX (HCl, HBr, HI)
3° alcohol → fastest (SN1)
1° alcohol → slowest (SN2)
📌 Lucas Test:
3° → immediate turbidity
2° → slow turbidity
1° → no turbidity (at room temp)
(B) Dehydration of Alcohols
Acid catalysed (conc. H₂SO₄)
Produces alkenes
Follows Saytzeff rule
📌 Ease of dehydration:
(C) Oxidation
1° alcohol → aldehyde → acid
2° alcohol → ketone
3° alcohol → resistant to oxidation
6. Some Commercially Important Alcohols
Methanol → solvent, fuel
Ethanol → beverages, antiseptic
Ethylene glycol → antifreeze
Glycerol → cosmetics, medicines
7. Phenols – Chemical Properties
(A) Acidic Nature
Phenol is more acidic than alcohol
Due to resonance stabilisation of phenoxide ion
📌 Order of acidity:
(B) Electrophilic Substitution
–OH group shows +R effect
Activates benzene ring
Directs substitution to ortho & para
📌 Important reactions:
Bromination → 2,4,6-tribromophenol
Nitration → o- & p-nitrophenol
(C) Reimer–Tiemann Reaction
Phenol + CHCl₃ + NaOH
Forms salicylaldehyde
(D) Kolbe’s Reaction
Sodium phenoxide + CO₂ (pressure)
Forms salicylic acid
8. Preparation of Phenol
From chlorobenzene
From cumene (industrial method)
From benzene via sulphonation
9. Ethers
Physical Properties
Lower boiling point than alcohols
Slightly soluble in water
Pleasant smell
Chemical Properties
(A) Williamson Ether Synthesis
Alkyl halide + sodium alkoxide
Proceeds via SN2
Best with primary alkyl halide
📌 Secondary & tertiary halides → elimination
(B) Reaction with HI
Cleavage of ether
Gives alkyl iodide + alcohol / phenol
10. Important Reason-Based Points (Exam Favourite)
✔ Phenol is more acidic than ethanol (resonance)
✔ o-Nitrophenol is steam volatile (intramolecular H-bonding)
✔ p-Nitrophenol has higher b.p. (intermolecular H-bonding)
✔ Ethers do not show hydrogen bonding
✔ 3° alcohols dehydrate fastest
✔ Williamson synthesis fails with tertiary halides
11. Order & Trends to Remember
Boiling Point
Acidity
Reactivity with HX
12. One-Line Revision (Last Minute)
Alcohol → substitution, elimination, oxidation
Phenol → acidic, o/p-directing, resonance
Ether → Williamson synthesis, cleavage by HI
–OH activates benzene ring
H-bonding controls b.p. & solubility
✍️ Top 10 Short Question–Answers (Board Exam Oriented)
What are alcohols?
Organic compounds in which –OH group is attached to an sp³ hybridised carbon.What are phenols?
Compounds in which –OH group is directly attached to a benzene ring.What are ethers?
Organic compounds having –O– linkage between two alkyl/aryl groups.Why do alcohols have higher boiling points than ethers?
Due to intermolecular hydrogen bonding in alcohols.What is Lucas test used for?
To distinguish between 1°, 2° and 3° alcohols.Which alcohol reacts fastest with HX?
Tertiary (3°) alcohol.Why is phenol more acidic than alcohol?
Due to resonance stabilisation of phenoxide ion.What is Williamson ether synthesis?
Preparation of ethers by reaction of alkyl halide with sodium alkoxide.Why do ethers have lower boiling points than alcohols?
Because ethers do not show hydrogen bonding.Which alcohol does not undergo oxidation easily?
Tertiary alcohol.
📝 Long Answer Questions
1. Classify alcohols, phenols and ethers with examples.
Alcohols (R–OH):
Primary (1°): R–CH₂–OH
Secondary (2°): R₂CH–OH
Tertiary (3°): R₃C–OH
Phenols:
–OH group directly attached to benzene ring
Example: C₆H₅OH
Ethers (R–O–R′):
Symmetrical ethers: R–O–R
Unsymmetrical ethers: R–O–R′
2. Explain chemical reactions of alcohols.
(a) Reaction with HX
3° alcohol → fastest (SN1)
1° alcohol → slowest (SN2)
Lucas Test:
3° → immediate turbidity
2° → slow turbidity
1° → no turbidity at room temperature
(b) Dehydration
Acid catalysed (conc. H₂SO₄)
Forms alkenes
Follows Saytzeff rule
(c) Oxidation
1° alcohol → aldehyde → acid
2° alcohol → ketone
3° alcohol → resistant to oxidation
3. Explain chemical properties of phenols.
(a) Acidic nature
Phenol is more acidic than alcohol
Due to resonance stabilisation of phenoxide ion
(b) Electrophilic substitution
–OH group activates benzene ring
Directs substitution to ortho and para positions
Important reactions:
Bromination → 2,4,6-tribromophenol
Nitration → o- and p-nitrophenol
(c) Reimer–Tiemann reaction
Phenol + CHCl₃ + NaOH → salicylaldehyde
(d) Kolbe’s reaction
Sodium phenoxide + CO₂ → salicylic acid
PYQs (Previous Years’ Questions – CBSE Board Oriented)
🔹 1 Mark PYQs
What are phenols?
Why do alcohols have higher boiling points than ethers?
Which alcohol reacts fastest with Lucas reagent?
What is the functional group present in ethers?
Why are tertiary alcohols resistant to oxidation?
Name the reaction used to prepare ethers from alkyl halides.
Which is more acidic: phenol or ethanol?
Why do ethers not show hydrogen bonding?
🔹 2 Mark PYQs
Differentiate between alcohols and phenols (any two points).
What is Lucas test? Write its use.
Why is phenol more acidic than alcohol?
What is Saytzeff rule?
Why does Williamson ether synthesis fail with tertiary alkyl halides?
Write two physical properties of alcohols.
What is Reimer–Tiemann reaction?
Write two uses of ethanol.
🔹 3 Mark PYQs
Explain dehydration of alcohols with mechanism and order of reactivity.
Explain acidic nature of phenol.
Describe Williamson ether synthesis with suitable example.
Explain oxidation reactions of primary and secondary alcohols.
Explain Kolbe’s reaction of phenol.
Why is o-nitrophenol steam volatile but p-nitrophenol is not?
🔹 5 Mark PYQs
(a) Classify alcohols with examples.
(b) Explain reactions of alcohols with HX.(a) Explain chemical properties of phenols.
(b) Why is phenol more acidic than ethanol?(a) What are ethers?
(b) Explain preparation of ethers by Williamson synthesis.(a) Explain Lucas test.
(b) How does it distinguish between 1°, 2° and 3° alcohols?(a) Describe preparation and properties of ethanol.
(b) Write its uses.
🔑 Most Repeated PYQ Areas (Exam Favourite)
✔ Phenol vs alcohol (acidity reasons)
✔ Lucas test
✔ Williamson ether synthesis
✔ Dehydration of alcohols
✔ Oxidation of alcohols
✔ o-Nitrophenol vs p-Nitrophenol
✔ Saytzeff rule
❓ FAQs (Concept Clarity)
Why does phenol show acidic behaviour?
Because phenoxide ion is stabilised by resonance.Why is o-nitrophenol steam volatile?
Due to intramolecular hydrogen bonding.Why does p-nitrophenol have higher boiling point?
Due to intermolecular hydrogen bonding.Why does Williamson ether synthesis fail with tertiary halides?
Because elimination reaction occurs instead of substitution.Why are lower alcohols soluble in water?
Due to hydrogen bonding with water molecules.
| Chapter No. | Chapter Name | Visit |
|---|---|---|
| 1 | The Solid State | Visit |
| 2 | Solutions | Visit |
| 3 | Electrochemistry | Visit |
| 4 | Chemical Kinetics | Visit |
| 5 | Surface Chemistry | Visit |
| 6 | General Principles and Processes of Isolation of Elements | Visit |
| 7 | The p-Block Elements | Visit |
| 8 | The d and f Block Elements | Visit |
| 9 | Coordination Compounds | Visit |
| 10 | Haloalkanes and Haloarenes | Visit |
| 11 | Alcohols, Phenols and Ethers | Visit |
| 12 | Aldehydes, Ketones and Carboxylic Acids | Visit |
| 13 | Amines | Visit |
| 14 | Biomolecules | Visit |
| 15 | Polymers | Visit |
| 16 | Chemistry in Everyday Life | Visit |
0 Comments