Introduction to NCERT Exemplar Solutions for Class 12 Chemistry Chapter 11: Alcohols, Phenols, and Ethers
Alcohols, phenols, and ethers are important classes of organic compounds containing oxygen atoms. These compounds not only occur widely in nature but also form the basis of many industrial and laboratory processes. Chapter 11 of Class 12 Chemistry explains their structure, properties, methods of preparation, and reactivity. The NCERT Exemplar Solutions for this chapter provide step-by-step guidance to complex problems, ensuring clarity of concepts and practice of higher-level reasoning.
Introduction to Alcohols, Phenols, and Ethers
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Alcohols contain a hydroxyl group attached to an alkyl chain, such as ethanol and methanol.
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Phenols are compounds where the hydroxyl group is bonded directly to an aromatic ring, such as phenol itself.
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Ethers contain an oxygen atom connected to two alkyl or aryl groups, for example, diethyl ether.
Exemplar questions introduce students to classification, structural variations, and the general importance of these compounds.
Methods of Preparation
The chapter covers several synthetic routes:
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Alcohols can be prepared from alkenes through hydration, from carbonyl compounds by reduction, and from haloalkanes through substitution.
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Phenols are obtained from haloarenes, diazonium salts, or by hydrolysis of aryl sulfonic acids.
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Ethers are prepared by Williamson’s synthesis, where an alkoxide reacts with a primary alkyl halide.
Exemplar solutions provide detailed reaction equations and mechanisms, helping students understand the logic behind each method.
Physical Properties
These compounds exhibit interesting physical properties due to hydrogen bonding and the polarity of their functional groups.
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Alcohols and phenols generally have higher boiling points compared to hydrocarbons of similar molecular weight.
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Solubility in water decreases as the size of the alkyl chain increases.
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Ethers have lower boiling points than alcohols of similar molecular mass because they cannot form hydrogen bonds with each other.
Exemplar questions often compare these properties across different compounds, strengthening conceptual understanding.
Chemical Properties
The reactivity of alcohols, phenols, and ethers depends on their functional groups:
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Alcohols undergo reactions such as oxidation to aldehydes and carboxylic acids, esterification with carboxylic acids, and dehydration to form alkenes.
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Phenols are more acidic than alcohols due to resonance stabilization of the phenoxide ion. They undergo electrophilic substitution reactions like nitration, halogenation, and sulphonation.
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Ethers are relatively inert but can be cleaved by strong acids such as hydrogen iodide or hydrogen bromide.
Exemplar solutions provide step-by-step mechanisms, ensuring that students can predict reaction pathways and products.
Mechanism of Reactions
This chapter emphasizes reaction mechanisms, such as the dehydration of alcohols, the electrophilic substitution of phenols, and the acid-catalyzed cleavage of ethers. Exemplar problems often ask students to justify why certain pathways are preferred or why reactivity differs between compounds.
Applications and Uses
Alcohols, phenols, and ethers have wide-ranging applications in daily life and industry:
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Alcohols: Ethanol is used in alcoholic beverages, as an industrial solvent, and as a fuel additive. Methanol is employed as an industrial feedstock.
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Phenols: Used in the manufacture of plastics, resins, antiseptics, and dyes.
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Ethers: Diethyl ether was historically used as an anesthetic and still finds use as a laboratory solvent.
Chemistry Exemplar questions frequently link these applications with theoretical knowledge, helping students appreciate the practical relevance of the topic.