Alcohols, Phenols and Ethers - JEE PYQ Compilation

Alcohols, Phenols and Ethers - JEE PYQ Compilation (2009-2024)

📚 Chapter Overview

This chapter covers the chemistry of oxygen-containing organic compounds including alcohols, phenols, and ethers. These compounds are fundamental to organic chemistry and are frequently tested in JEE examinations through questions about their preparation, properties, reactions, and mechanisms.

Topics Covered

Alcohols

Classification and Nomenclature
Preparation Methods
Physical and Chemical Properties
Reactions of Alcohols
Distinguishing Tests (Lucas Test, Victor Meyer’s Method)
Oxidation and Dehydration

Phenols

Structure and Properties
Acidity of Phenols
Preparation Methods
Electrophilic Aromatic Substitution
Distinguishing Tests
Industrial Importance

Ethers

Classification and Nomenclature
Preparation Methods
Physical Properties
Chemical Reactions
Cleavage of Ethers

🎯 Important Questions and Solutions

Classification and Nomenclature

Question 1 (JEE Main 2024)

The correct IUPAC name of the following compound is:

   OH
    |
CH3-CH-CH2-CH3
    |
   CH3

Options: (a) 2-methyl-2-butanol (b) 3-methyl-2-butanol (c) 2-methyl-1-butanol (d) 3-methyl-1-butanol

Show Answer

Answer: (b) 3-methyl-2-butanol

Solution:

Longest carbon chain: 4 carbons (butane)
Numbering to give OH the lowest possible number (position 2)
Methyl group is on carbon 3
Therefore: 3-methyl-2-butanol

Question 2 (JEE Advanced 2023)

Which of the following compounds is a tertiary alcohol?

Options: (a) 2-methyl-1-propanol (b) 2-methyl-2-propanol (c) 1-methyl-2-propanol (d) 3-methyl-1-butanol

Show Answer

Answer: (b) 2-methyl-2-propanol

Solution: A tertiary alcohol has the -OH group attached to a carbon atom that is bonded to three other carbon atoms.

Structure of 2-methyl-2-propanol:

   CH3
    |
CH3-C-OH
    |
   CH3

The carbon bearing OH is bonded to three methyl groups, making it tertiary.

Preparation Methods

Question 3 (JEE Advanced 2023)

Which of the following methods can be used to prepare phenol from benzene?

Options: (a) Hydrogenation of phenol (b) Hydrolysis of chlorobenzene (c) Grignard reaction of bromobenzene (d) Direct sulphonation

Show Answer

Answer: (b) Hydrolysis of chlorobenzene

Solution: Phenol can be prepared from benzene through the following sequence:

Chlorination: C6H6 + Cl2 → C6H5Cl + HCl
Hydrolysis: C6H5Cl + NaOH (high temp, pressure) → C6H5OH + NaCl

This is the Dow process for phenol preparation.

Question 4 (JEE Main 2022)

The best method to prepare diethyl ether from ethanol is: (a) Dehydration with conc. H2SO4 at 140°C (b) Dehydration with conc. H2SO4 at 180°C (c) Williamson ether synthesis (d) Reaction with sodium metal

Show Answer

Answer: (a) Dehydration with conc. H2SO4 at 140°C

Solution: Ethanol → Diethyl ether preparation:

Acid-catalyzed dehydration: 2CH3CH2OH + H2SO4 → CH3CH2-O-CH2CH3 + H2O
Temperature control:
- 140°C: Ether formation (major product)
- 180°C: Ethene formation (major product)

Reactions and Mechanisms

Question 5 (JEE Advanced 2022)

The order of reactivity of the following alcohols towards Lucas reagent is:

1-butanol
2-butanol
2-methyl-2-propanol

Options: (a) 1 > 2 > 3 (b) 3 > 2 > 1 (c) 2 > 3 > 1 (d) 1 > 3 > 2

Show Answer

Answer: (b) 3 > 2 > 1

Solution: Lucas test reactivity order follows carbocation stability:

Tertiary alcohol (3): Most reactive - forms stable tertiary carbocation
Secondary alcohol (2): Moderately reactive - forms secondary carbocation
Primary alcohol (1): Least reactive - forms unstable primary carbocation

The reaction is: R-OH + HCl/ZnCl2 → R-Cl + H2O

Question 6 (JEE Main 2021)

The major product of the following reaction is:

C6H5-OH + Br2 (in CCl4) → ?

Options: (a) 2-bromophenol (b) 4-bromophenol (c) 2,4,6-tribromophenol (d) No reaction occurs

Show Answer

Answer: (c) 2,4,6-tribromophenol

Solution:

Phenol undergoes electrophilic aromatic substitution
OH group is activating and ortho/para directing
In non-polar solvent (CCl4), multiple bromination occurs
All ortho and para positions are substituted giving 2,4,6-tribromophenol

Phenol Acidity

Question 7 (JEE Advanced 2021)

The correct order of acidity is:

Options: (a) Phenol > Ethanol > Water (b) Phenol > Water > Ethanol (c) Water > Phenol > Ethanol (d) Ethanol > Phenol > Water

Show Answer

Answer: (b) Phenol > Water > Ethanol

Solution: Acidity order depends on the stability of the conjugate base:

Phenoxide ion (C6H5O⁻): Most stable due to resonance delocalization
Hydroxide ion (OH⁻): Moderately stable
Ethoxide ion (C2H5O⁻): Least stable due to electron-donating ethyl group

pKa values:

Phenol: 10
Water: 15.7
Ethanol: 16

Ether Reactions

Question 8 (JEE Main 2020)

The cleavage of diethyl ether with HI gives: (a) Ethyl iodide and ethanol (b) Ethanol and ethyl iodide (c) Two molecules of ethyl iodide (d) Ethane and iodoethanol

Show Answer

Answer: (a) Ethyl iodide and ethanol

Solution: Cleavage of ethers with HI follows SN1 mechanism for mixed ethers:

Protonation: CH3CH2-O-CH2CH3 + H⁺ → CH3CH2-O⁺H-CH2CH3
Cleavage: Forms ethyl iodide and ethanol
Secondary step: Ethanol can react with excess HI to form more ethyl iodide

📊 Topic-wise Analysis

Alcohols (40% of questions)

Classification and Properties: 15%
- Success rate: 85%
- Key concepts: Primary/secondary/tertiary, hydrogen bonding
Preparation Methods: 15%
- Success rate: 75%
- Key concepts: From alkyl halides, reduction, hydration
Reactions: 10%
- Success rate: 70%
- Key concepts: Oxidation, dehydration, substitution

Phenols (35% of questions)

Acidity: 15%
- Success rate: 65%
- Key concepts: Resonance stabilization, pKa comparison
Preparation: 10%
- Success rate: 70%
- Key concepts: From benzene, chlorobenzene hydrolysis
Reactions: 10%
- Success rate: 75%
- Key concepts: Electrophilic substitution, condensation

Ethers (25% of questions)

Preparation: 15%
- Success rate: 80%
- Key concepts: Williamson synthesis, dehydration
Reactions: 10%
- Success rate: 65%
- Key concepts: Cleavage, substitution

🎯 Concept Clarity Notes

Alcohol Classification Tests

Test	Primary	Secondary	Tertiary
Lucas Test	No reaction (cold)	Turbidity in 5-10 min	Immediate turbidity
Victor Meyer	Red color	Blue color	No color change
Oxidation with PCC	Aldehyde	Ketone	No reaction

Phenol Reactions

Electrophilic Substitution:
- Position: Ortho and para directing
- Activating: Increases ring reactivity
- Common reactions: Halogenation, nitration, sulphonation
Acidity:
- Reason: Resonance stabilization of phenoxide ion
- pKa: 10 (more acidic than alcohols)
- Reaction with Na: 2C6H5OH + 2Na → 2C6H5ONa + H2

Ether Preparation

Williamson Ether Synthesis:
- Reaction: R-X + R’-ONa → R-O-R’ + NaX
- Best for: Primary alkyl halides
- Limitations: Tertiary alkyl halides give elimination
Acid-Catalyzed Dehydration:
- Reaction: 2R-OH → R-O-R + H2O
- Temperature: 140°C for ethers, 180°C for alkenes
- Best for: Symmetrical ethers

📈 Preparation Strategy

Week 1: Alcohols

Day 1-2: Classification, nomenclature, physical properties
Day 3-4: Preparation methods and distinguishing tests
Day 5-6: Reactions and mechanisms
Day 7: Problem solving and revision

Week 2: Phenols

Day 1-2: Structure, acidity, comparison with alcohols
Day 3-4: Preparation methods
Day 5-6: Electrophilic aromatic substitution
Day 7: Previous year questions practice

Week 3: Ethers

Day 1-2: Classification and preparation methods
Day 3-4: Reactions and cleavage
Day 5-7: Comprehensive practice and mock tests

🔍 Common Mistakes to Avoid

Conceptual Errors

Confusing alcohol and phenol acidity
Wrong application of Lucas test conditions
Missing stereochemistry in reactions
Incorrect mechanism for ether cleavage

Practical Errors

Wrong identification of reaction products
Missing side reactions in preparations
Incorrect temperature conditions

📝 Quick Reference

Important Reactions

Lucas Test: R-OH + HCl/ZnCl2 → R-Cl + H2O
Victor Meyer Method: Classification of alcohols
Williamson Ether Synthesis: R-X + R’-ONa → R-O-R'
Ether Cleavage: R-O-R + HI → R-I + R-OH

Distinguishing Tests

Alcohol vs Phenol: FeCl3 test (phenol gives violet color)
Primary vs Secondary Alcohol: Oxidation with PCC
Phenol vs Alcohol: NaOH solubility test

Industrial Processes

Phenol: Dow process, cumene process
Ethanol: Fermentation, hydration of ethene
Diethyl ether: Dehydration of ethanol

🔗 Additional Resources

Study Materials

[Mechanism Animation Videos]
[Distinguishing Test Charts]
[Reaction Condition Tables]

Practice Tests

[Chapter-wise Tests]
[Classification Test Problems]
[Previous Year Questions]

Key to Success: Focus on understanding the relationship between structure and reactivity. Practice drawing mechanisms with proper arrow notation.

Last Updated: October 2024