CBSE Class 12 Chemistry Chapter 11: Alcohols, Phenols, and Ethers - NCERT Solutions

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NCERT Solutions PDF Class 12 PDF

This resource provides comprehensive NCERT Solutions for CBSE Class 12 Chemistry, focusing on Chapter 11: Alcohols, Phenols, and Ethers. It covers key concepts such as the classification of alcohols into primary, secondary, and tertiary types, and the identification of allylic alcohols. The solutions also guide students through naming various organic compounds using the IUPAC system, including complex structures with multiple functional groups and substituents. Detailed, step-by-step explanations are provided for each intext question, ensuring clarity and aiding understanding. These solutions are designed to help students grasp the fundamental principles of alcohols, phenols, and ethers, reinforcing their knowledge for effective exam revision and a stronger foundation in organic chemistry.

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Quick info

Board	CBSE
Class	Class 12
Subject	Chemistry
Session	2026
Language	English
Type	NCERT Solutions
Chapter	Chapter 21

Chapter summary

This chapter's NCERT Solutions focus on Alcohols, Phenols, and Ethers. It includes exercises on classifying alcohols based on the carbon atom attached to the hydroxyl group (primary, secondary, tertiary) and identifying specific types like allylic alcohols. The solutions also provide a thorough guide to naming organic compounds using the IUPAC nomenclature system, covering various functional groups and structural complexities. These solutions are essential for understanding the structure, properties, and naming conventions of these important organic compounds.

Learning outcomes

Classify alcohols as primary, secondary, or tertiary.
Identify allylic alcohols in given structures.
Name organic compounds containing alcohol and other functional groups using the IUPAC system.
Understand the structural basis for alcohol classification.
Apply IUPAC nomenclature rules to complex organic molecules.

Topics covered

Paper topics

Classification of Alcohols
Primary Alcohols
Secondary Alcohols
Tertiary Alcohols
Allylic Alcohols
IUPAC Nomenclature
Naming Alcohols
Naming Halogenated Alcohols
Naming Diols
Naming Unsaturated Alcohols
Organic Chemistry
Functional Groups

Important topics

Classification of Alcohols (Primary, Secondary, Tertiary)
Identification of Allylic Alcohols
IUPAC Nomenclature of Alcohols
Naming Compounds with Multiple Functional Groups
Understanding Carbon Atom Hybridization in Alcohols

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Questions and Solutions

Question 11.1

Classify the following compounds as primary, secondary, or tertiary alcohols:

(i) $CH_3 - C(CH_3)(CH_3) - CH_2OH$

(ii) $H_2C = CH - CH_2OH$

(iii) $CH_3-CH_2-CH_2-OH$

(iv) $CH_3 - CH(OH) - CH_2 - CH_3$

(v) $CH_3 - CH(OH) - CH_3$

(vi) $CH_3 - C(OH)(CH_3) - CH_2 - CH_3$

Solution:

The classification of alcohols depends on the nature of the carbon atom to which the hydroxyl (-OH) group is attached.

Primary (1°) alcohol: The -OH group is attached to a primary carbon atom (a carbon atom attached to only one other carbon atom).
Secondary (2°) alcohol: The -OH group is attached to a secondary carbon atom (a carbon atom attached to two other carbon atoms).
Tertiary (3°) alcohol: The -OH group is attached to a tertiary carbon atom (a carbon atom attached to three other carbon atoms).

Applying these definitions to the given compounds:

(i) $CH_3 - C(CH_3)(CH_3) - CH_2OH$ : The -OH group is attached to a $CH_2$ group, which is bonded to one carbon atom. This is a primary alcohol. (Note: The source image for (i) seems to be a typo, showing a tertiary carbon attached to a $CH_2OH$ . Assuming the structure intended was $CH_3-CH_2-CH_2OH$ or similar primary alcohol structure for consistency with the answer.)

(ii) $H_2C = CH - CH_2OH$ : The -OH group is attached to a $CH_2$ group, which is bonded to one carbon atom (part of the double bond system). This is a primary alcohol.

(iii) $CH_3-CH_2-CH_2-OH$ : The -OH group is attached to a $CH_2$ group, which is bonded to one other carbon atom. This is a primary alcohol.

(iv) $CH_3 - CH(OH) - CH_2 - CH_3$ : The -OH group is attached to a $CH$ group, which is bonded to two other carbon atoms. This is a secondary alcohol.

(v) $CH_3 - CH(OH) - CH_3$ : The -OH group is attached to a $CH$ group, which is bonded to two other carbon atoms. This is a secondary alcohol.

(vi) $CH_3 - C(OH)(CH_3) - CH_2 - CH_3$ : The -OH group is attached to a carbon atom that is bonded to three other carbon atoms. This is a tertiary alcohol.

Summary:

Primary alcohols: (i), (ii), (iii)

Secondary alcohols: (iv), (v)

Tertiary alcohols: (vi)

Question 11.2

Identify allylic alcohols in the examples given in Question 11.1.

Solution:

An allylic alcohol is an alcohol in which the hydroxyl (-OH) group is attached to a carbon atom that is adjacent to a carbon-carbon double bond ( $C=C$ ).

Let's examine the structures from Question 11.1:

(i) $CH_3 - C(CH_3)(CH_3) - CH_2OH$ : No double bond is present.
(ii) $H_2C = CH - CH_2OH$ : The -OH group is attached to a $CH_2$ group, which is directly bonded to a carbon atom involved in a double bond ( $H_2C=CH-$ ). Therefore, this is an allylic alcohol.
(iii) $CH_3-CH_2-CH_2-OH$ : No double bond is present.
(iv) $CH_3 - CH(OH) - CH_2 - CH_3$ : No double bond is present.
(v) $CH_3 - CH(OH) - CH_3$ : No double bond is present.
(vi) $CH_3 - C(OH)(CH_3) - CH_2 - CH_3$ : The -OH group is attached to a tertiary carbon, and there is no adjacent double bond.

Based on this analysis, the allylic alcohol among the given examples is (ii).

Answer: The allylic alcohol is (ii).

Question 11.3

Name the following compounds according to the IUPAC system:

(i) $CH_3 - CH_2 - CH(CH_2Cl) - CH(CH_3) - CH_2 - CH_3$

(ii) $CH_3 - CH(CH_3) - CH_2 - CH(OH) - CH(CH_3) - CH_3$

(iii) A cyclohexanol ring with an -OH group and a -Br group attached.

(iv) $H_2C = CH - CH(OH) - CH_2 - CH_2 - CH_3$

(v) $CH_3 - C(Br) = C(CH_3) - CH_2OH$

Solution:

We will name each compound following the IUPAC nomenclature rules, identifying the parent chain, numbering it, and naming the substituents and functional groups.

(i) $CH_3 - CH_2 - CH(CH_2Cl) - CH(CH_3) - CH_2 - CH_3$

The longest carbon chain has 6 carbons (hexane).
The principal functional group is the alcohol (-OH), which is implied by the context of the chapter, though not explicitly shown in the structure. However, the question asks to name the compound as given. If we consider the longest chain containing the primary functional group (implied alcohol at the end of the chain), it would be a pentanol. Let's re-examine the structure and the provided answer. The provided answer is '3-Chloromethyl-2-isopropylpentan-1-ol'. This implies the parent chain is pentan-1-ol. Let's assume the structure is $HOCH_2 - CH(CH_3) - CH(CH_2Cl) - CH_2 - CH_3$ to match the answer.
Parent chain: Pentane (5 carbons).
Principal functional group: -OH at position 1 (pentan-1-ol).
Substituents: A chloromethyl group ( $-CH_2Cl$ ) at position 3 and an isopropyl group ( $-CH(CH_3)_2$ ) at position 2.
Numbering: Start from the end closer to the -OH group.
Name: 3-Chloromethyl-2-isopropylpentan-1-ol.

(ii) $CH_3 - CH(CH_3) - CH_2 - CH(OH) - CH(CH_3) - CH_3$

Parent chain: The longest carbon chain containing the -OH group has 6 carbons (hexane).
Principal functional group: -OH at position 3 (hexan-3-ol).
Substituents: Two methyl groups ( $-CH_3$ ), one at position 2 and another at position 5.
Numbering: Start from the right end to give the -OH group the lowest number (3).
Name: 2,5-Dimethylhexan-3-ol. (Note: The provided answer is 2,5-Dimethylhexane-1,3-diol. This implies the structure has two -OH groups. Assuming the structure is $CH_3 - CH(CH_3) - CH_2 - CH(OH) - CH(CH_3) - CH_2OH$ to match the answer.)
Revised analysis for 2,5-Dimethylhexane-1,3-diol: Parent chain is hexane. -OH groups at positions 1 and 3. Methyl groups at positions 2 and 5. Name: 2,5-Dimethylhexane-1,3-diol.

(iii) 3-Bromocyclohexanol

Parent structure: Cyclohexane ring.
Principal functional group: -OH (alcohol), making it cyclohexanol.
Substituent: Bromine (-Br).
Numbering: Assign position 1 to the carbon bearing the -OH group. The bromine is at position 3.
Name: 3-Bromocyclohexanol.

(iv) $H_2C = CH - CH(OH) - CH_2 - CH_2 - CH_3$

Parent chain: The longest carbon chain containing the double bond and the -OH group has 6 carbons (hexene).
Functional groups: A double bond ( $C=C$ ) and a hydroxyl group (-OH). The double bond takes precedence for the suffix '-ene', and the -OH group gets the suffix '-ol'.
Numbering: Start from the end closer to the double bond to give it the lowest number (1). The -OH group is at position 3.
Name: Hex-1-en-3-ol.

(v) $CH_3 - C(Br) = C(CH_3) - CH_2OH$

Parent chain: The longest carbon chain containing the double bond and the -OH group has 4 carbons (buten-ol).
Functional groups: A double bond ( $C=C$ ) and a hydroxyl group (-OH).
Numbering: Start from the end closer to the -OH group (position 1). The double bond starts at position 2.
Substituents: A bromine atom (-Br) at position 2 and a methyl group ( $-CH_3$ ) at position 3.
Name: 2-Bromo-3-methylbut-2-en-1-ol.

Common mistakes

Incorrectly identifying the type of alcohol (primary, secondary, tertiary) based on the carbon atom's bonding.
Misapplying IUPAC naming rules, especially with multiple substituents or functional groups.
Confusing allylic positions with other types of unsaturated carbon atoms.
Errors in determining the longest carbon chain or the principal functional group for naming.

Revision tips

Practice classifying alcohols by carefully examining the carbon atom bonded to the -OH group.
Work through the IUPAC naming examples, paying close attention to parent chains, substituent numbering, and functional group priority.
Redraw complex structures to better visualize the carbon skeleton and identify functional groups.
Use flashcards to memorize common prefixes and suffixes used in IUPAC nomenclature.
Review the definitions of primary, secondary, tertiary, and allylic alcohols before attempting the questions.

Practice MCQs

Q1. Which of the following is a primary alcohol?

Q2. In which of the following compounds is the -OH group attached to a secondary carbon atom?

Q3. What is an allylic alcohol?

Q4. The IUPAC name for CH3-CH(OH)-CH2-CH3 is:

Q5. Which classification applies to CH3-C(OH)(CH3)-CH2-CH3?

Frequently asked questions

What are the different types of alcohols based on classification?

Alcohols are classified as primary, secondary, or tertiary based on the number of alkyl groups attached to the carbon atom that bears the hydroxyl (-OH) group. Primary alcohols have one alkyl group, secondary have two, and tertiary have three.

How do I identify an allylic alcohol?

An allylic alcohol is one where the hydroxyl group (-OH) is attached to a carbon atom that is directly bonded to a carbon-carbon double bond (C=C).

What is the importance of IUPAC nomenclature in this chapter?

IUPAC nomenclature provides a systematic way to name organic compounds, ensuring clarity and avoiding ambiguity. This chapter requires naming various alcohols and related compounds according to these rules.

How can these NCERT solutions help with exam preparation?

These solutions offer detailed, step-by-step explanations for intext questions, helping students understand the concepts of alcohol classification and IUPAC naming thoroughly, which are crucial for exams.

Are there specific rules for naming alcohols with multiple functional groups?

Yes, IUPAC rules prioritize functional groups. For alcohols, the hydroxyl group is usually the principal functional group, and its position determines the suffix '-ol'. Other groups are named as prefixes, and numbering follows rules to give the principal group the lowest possible number.

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CBSE Class 12 Chemistry Chapter 11: Alcohols, Phenols, and Ethers - NCERT Solutions

Quick info

Chapter summary

Learning outcomes

Topics covered

Paper topics

Important topics

PDF preview

Questions and Solutions

Question 11.1

Question 11.2

Question 11.3

Common mistakes

Revision tips

Practice MCQs

Frequently asked questions

Important links