Introduction to NCERT Exemplar Solutions for Class 12 Chemistry Chapter 13: Amines
Amines are organic compounds derived from ammonia by replacing one or more hydrogen atoms with alkyl or aryl groups. They are important due to their occurrence in nature, industrial applications, and role as intermediates in the synthesis of medicines, dyes, and polymers. Chapter 13 of Class 12 Chemistry focuses on the structure, classification, properties, and reactions of amines. The Chemistry NCERT Exemplar Solutions provide detailed explanations of conceptual and numerical problems, enabling students to understand this functional group with clarity. Check out NCERT solutions for class 12 Chemistry.
Introduction and Classification of Amines
Amines are classified based on the number of hydrogen atoms substituted by alkyl or aryl groups:
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Primary amines: One hydrogen atom replaced, for example, methylamine and aniline.
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Secondary amines: Two hydrogen atoms replaced, such as dimethylamine.
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Tertiary amines: All three hydrogen atoms replaced, such as trimethylamine.
Exemplar questions test students’ ability to identify and classify amines based on structure and nomenclature.
Nomenclature of Amines
The International Union of Pure and Applied Chemistry (IUPAC) rules are used for naming amines. Primary amines are named as alkylamines or arylamines, depending on the group attached. Secondary and tertiary amines are named according to the groups present on nitrogen. Exemplar problems ensure students practice systematic naming and avoid confusion in structural representation.
Methods of Preparation
This chapter explains multiple synthetic routes to prepare amines:
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Reduction of nitro compounds using catalytic hydrogenation or metals in acidic medium.
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Reduction of nitriles and amides to obtain primary amines.
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Gabriel phthalimide synthesis to produce pure primary amines.
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Hofmann bromamide degradation of amides, yielding primary amines with one carbon less.
Exemplar solutions highlight mechanisms and stepwise reasoning behind these methods, strengthening conceptual clarity.
Physical Properties
The physical properties of amines depend on intermolecular hydrogen bonding and polarity:
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Lower amines are soluble in water due to hydrogen bonding.
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Boiling points are higher than hydrocarbons of similar molecular mass but lower than alcohols.
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Amines often have a characteristic fishy odor.
Exemplar questions involve comparing properties across primary, secondary, and tertiary amines based on bonding and molecular structure.
Chemical Properties
Amines are basic in nature due to the presence of a lone pair on the nitrogen atom. The extent of basicity depends on the type of amine and the solvent.
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Reactions as bases: Amines react with acids to form ammonium salts.
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Alkylation: Reaction with alkyl halides to form higher amines.
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Acylation: Reaction with acid chlorides or anhydrides to give amides.
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Carbylamine reaction: Primary amines react with chloroform and alcoholic potassium hydroxide to produce isocyanides with a foul odor.
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Diazotization of aromatic amines: Aniline reacts with nitrous acid to form diazonium salts, which are versatile intermediates in organic synthesis.
Exemplar questions often focus on predicting reaction products and explaining differences in reactivity among primary, secondary, and tertiary amines.
Applications of Diazonium Salts
Aromatic diazonium salts are important intermediates in the synthesis of dyes, azo compounds, and other aromatic derivatives. They undergo substitution reactions to yield phenols, halides, and cyanides. Exemplar solutions explain the significance of diazonium salts in industrial chemistry.
Uses and Applications of Amines
Amines have wide applications in industry and medicine:
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Used in the production of dyes, polymers, and pharmaceuticals.
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Aniline is essential in the synthesis of rubber processing chemicals and drugs.
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Aliphatic amines serve as intermediates in pesticide and drug manufacturing.
Exemplar questions often connect these applications with theoretical knowledge, allowing students to understand the real-world significance of amines.