Organic Chemistry is one of the most scoring yet concept-based sections of Class 12 Chemistry, and among its chapters,Class 12 Alcohols Phenols and Ethers Notes plays a very important role. Questions from this chapter are frequently asked in CBSE Board Exams, NEET, CUET, and other competitive exams.
This chapter mainly deals with oxygen-containing organic compounds, their structure, nomenclature, preparation methods, physical and chemical properties, and important reactions. A strong understanding of this chapter helps students easily solve reaction-based, mechanism-based, and numerical questions.
These notes are prepared in a student-friendly, exam-focused manner with formulas, reactions, examples, and important points, so that students can revise quickly and score high marks.
Class 12 Alcohols, Phenols and Ethers Notes – NCERT, Important Reactions & Formulas
1. Alcohols
Definition
Alcohols are organic compounds in which the hydroxyl group (–OH) is attached to a saturated carbon atom (sp³ hybridized).
General Formula
\text{R–OH}
Classification of Alcohols
(a) Based on number of –OH groups
- Monohydric alcohol: One –OH group (Ethanol)
- Dihydric alcohol: Two –OH groups (Ethylene glycol)
- Trihydric alcohol: Three –OH groups (Glycerol)
(b) Based on carbon attached to –OH
- Primary (1°) alcohol: –OH attached to carbon bonded with one alkyl group
Example: Ethanol (CH₃CH₂OH) - Secondary (2°) alcohol: –OH attached to carbon bonded with two alkyl groups
Example: Isopropyl alcohol - Tertiary (3°) alcohol: –OH attached to carbon bonded with three alkyl groups
Example: tert-Butyl alcohol
IUPAC Nomenclature of Alcohols
- Select the longest carbon chain containing –OH group
- Replace suffix –e of alkane with –ol
- Number the chain to give –OH lowest locant
Example:
CH₃CH₂OH → Ethanol
Preparation of Alcohols
(1) From Alkyl Halides
\text{R–X} + \text{KOH (aq)} \rightarrow \text{R–OH} + \text{KX}
(2) By Reduction of Aldehydes and Ketones
\text{R–CHO} \xrightarrow{[H]} \text{R–CH}_2\text{OH}
\text{R–CO–R’} \xrightarrow{[H]} \text{R–CHOH–R’}
Physical Properties of Alcohols
- Higher boiling points due to hydrogen bonding
- Soluble in water (lower alcohols)
- Boiling point increases with molecular mass
Chemical Properties of Alcohols
(1) Reaction with Sodium
2\text{R–OH} + 2\text{Na} \rightarrow 2\text{R–ONa} + \text{H}_2
(2) Dehydration Reaction
\text{R–OH} \xrightarrow{conc.\ H_2SO_4} \text{Alkene} + \text{H}_2O
(3) Oxidation
- 1° alcohol → Aldehyde → Acid
- 2° alcohol → Ketone
- 3° alcohol → No oxidation
2. Phenols
Definition
Phenols are compounds in which the –OH group is directly attached to an aromatic ring.
General Formula
\text{Ar–OH}
Preparation of Phenol
(1) From Chlorobenzene (Dow Process)
\text{C}_6\text{H}_5\text{Cl} \xrightarrow{NaOH, 623K} \text{C}_6\text{H}_5\text{ONa}
\rightarrow \text{Phenol}
Physical Properties of Phenols
- Higher boiling point
- Slightly soluble in water
- Strong intermolecular hydrogen bonding
Chemical Properties of Phenols
(1) Acidic Nature
Phenol is more acidic than alcohol due to resonance stabilization.
(2) Reaction with NaOH
\text{C}_6\text{H}_5\text{OH} + \text{NaOH} \rightarrow \text{C}_6\text{H}_5\text{ONa} + \text{H}_2\text{O}
(3) Electrophilic Substitution
- Nitration
\text{Phenol} + \text{HNO}_3 \rightarrow \text{o-, p-Nitrophenol}
Important Test
- Ferric Chloride Test: Violet coloration confirms phenol
3. Ethers
Definition
Ethers are compounds in which an oxygen atom is bonded to two alkyl or aryl groups.
General Formula
\text{R–O–R'}
Nomenclature of Ethers
- Smaller alkyl group → alkoxy
- Larger alkyl group → alkane
Example:
CH₃OCH₂CH₃ → Methoxyethane
Preparation of Ethers
(1) Williamson Ether Synthesis
\text{R–ONa} + \text{R'–X} \rightarrow \text{R–O–R'}
Physical Properties
- Low boiling point
- Pleasant smell
- Insoluble in water
Chemical Properties
(1) Cleavage with HI
\text{R–O–R'} + \text{HI} \rightarrow \text{R–I} + \text{R'–OH}
Important Formulas & Key Points
- Boiling point: Phenol > Alcohol > Ether
- Acidity order: Phenol > Alcohol > Ether
- Hydrogen bonding present in alcohols & phenols
- Ethers are least reactive
Example Questions
Example 1
Why phenol is more acidic than alcohol?
Answer: Due to resonance stabilization of phenoxide ion.
Example 2
Write the product of ethanol with conc. H₂SO₄ at 443 K.
Answer: Ethene
Conclusion
The chapter Alcohols, Phenols and Ethers is extremely important for Class 12 Chemistry and competitive exams. If students understand the concepts, reactions, mechanisms, and formulas, this chapter becomes very easy and scoring. Regular revision using short notes, reaction charts, and examples will help students secure full marks.
Repeated Questions – Alcohols Phenols and Ethers (Class 12)
Q1. Why phenol is more acidic than alcohol? (Very Repeated)
Answer:
Phenol alcohol se zyada acidic hota hai kyunki phenol se proton nikalne ke baad banne wala phenoxide ion resonance stabilized hota hai. Jabki alcohol me banne wala alkoxide ion resonance stabilized nahi hota.
👉 Order of acidity:
Phenol > Alcohol > Ether
Q2. Why alcohols have higher boiling points than ethers?
Answer:
Alcohols me intermolecular hydrogen bonding hoti hai due to –OH group, jabki ethers me hydrogen bonding absent hoti hai. Isliye alcohols ka boiling point ethers se zyada hota hai.
Q3. Write the reaction of ethanol with sodium metal.
Answer:
2CH_3CH_2OH + 2Na \rightarrow 2CH_3CH_2ONa + H_2 \uparrow
👉 Is reaction me hydrogen gas evolve hoti hai.
Q4. What happens when ethanol is heated with concentrated H₂SO₄ at 443 K?
Answer:
Ethanol dehydration ke through ethene gas banata hai.
CH_3CH_2OH \xrightarrow{conc.\ H_2SO_4,\ 443K} CH_2=CH_2 + H_2O
Q5. Explain Williamson Ether Synthesis. (Most Important)
Answer:
Williamson Ether Synthesis me alkoxide ion ko alkyl halide ke saath react karaya jata hai jisse ether banta hai.
R–ONa + R'–X \rightarrow R–O–R' + NaX
👉 Ye reaction SN2 mechanism follow karti hai.
Q6. Why phenol does not give alcohol tests?
Answer:
Phenol me –OH group aromatic ring se directly attached hota hai, jabki alcohol me –OH group alkyl group se attached hota hai. Isliye phenol alcohol tests nahi deta.
Q7. Write Ferric Chloride test for phenol.
Answer:
Phenol neutral FeCl₃ solution ke saath react karke violet color deta hai.
Phenol + FeCl_3 \rightarrow Violet\ Complex
👉 Ye phenol ka confirmatory test hai.
Q8. Why ethers are less reactive than alcohols?
Answer:
Ethers me –OH group absent hota hai aur oxygen ke lone pairs stable hote hain. Isliye ethers alcohols ke comparison me kam reactive hote hain.
Q9. Give the order of boiling points of alcohol, phenol and ether.
Answer:
Phenol > Alcohol > Ether
👉 Reason: Hydrogen bonding strength
Q10. What happens when ether reacts with excess HI?
Answer:
Ether cleavage hota hai aur alkyl iodide aur alcohol banta hai.
R–O–R' + HI \rightarrow R–I + R'–OH
(Excess HI me dono side iodide ban sakte hain)
Q11. Distinguish between Alcohol and Phenol. (Board Favourite)
| Alcohol | Phenol |
|---|---|
| –OH alkyl group se attached | –OH aromatic ring se attached |
| Weakly acidic | More acidic |
| NaOH se react nahi karta | NaOH se react karta hai |
Q12. Write IUPAC name of CH₃OCH₂CH₃.
Answer:
👉 Methoxyethane
Q13. Why tertiary alcohols do not undergo oxidation easily?
Answer:
Tertiary alcohols me α-hydrogen absent hota hai, isliye oxidation difficult hoti hai.
Q14. Name one important use of phenol.
Answer:
Phenol ka use:
- Disinfectant
- Bakelite (plastic) banane me
- Drugs aur dyes me
Q15. Which alcohol gives Lucas test immediately?
Answer:
👉 Tertiary alcohol gives immediate turbidity in Lucas test.
Complete Class 12 Alcohols Phenols and Ethers Notes