Class 12 Chemistry - HARYANA
Amines
The chapter 'Amines' in Class 12 Chemistry explores derivatives of ammonia where one or more hydrogen atoms are replaced by alkyl or aryl groups. Students learn about the classification, nomenclature, and general methods of preparation of aliphatic and aromatic amines, including reduction of nitro compounds and Hoffmann bromamide degradation. The physical and chemical properties are discussed in detail, highlighting their basic character and nucleophilic nature. Special emphasis is given to diazonium salts as synthetic intermediates for preparing various aromatic compounds. This chapter holds high weightage in Haryana (BSEH) board exams, frequently featuring direct name reactions, conversion problems, and reasoning questions.
Start Learning FreeKey Concepts
Classification and Structure
Amines are classified as primary (1°), secondary (2°), or tertiary (3°) depending on the number of hydrogen atoms replaced by alkyl or aryl groups on the nitrogen atom.
Basic Strength of Amines
Amines act as Lewis bases due to the presence of an unshared electron pair on nitrogen. Basic strength varies in aqueous and gaseous phases depending on inductive effect, steric hindrance, and solvation effect.
Hoffmann Bromamide Degradation
A standard method to prepare primary amines by treating an amide with bromine and caustic alkali, resulting in the descent of the series with the loss of one carbon atom.
Carbylamine Test
A chemical test used to distinguish primary amines by heating them with chloroform and ethanolic potassium hydroxide, producing foul-smelling isocyanides.
Diazonium Salts
Stable compounds with the general formula ArN2+ X- prepared by diazotization of primary aromatic amines, widely used for coupling and substitution reactions in synthetic chemistry.
Important Formulas
Board Exam Info
In the Haryana (BSEH) Class 12 Chemistry board exam, the chapter 'Amines' typically carries around 4 to 6 marks. Common question types include chemical conversions (e.g., nitrobenzene to aniline), naming reactions like Hoffmann bromamide degradation, distinguishing tests such as the carbylamine test and Hinsberg test, and reasoning questions based on boiling points and basic character.
Frequently Asked Questions
Why are aliphatic amines stronger bases than ammonia?
Aliphatic amines have alkyl groups that exert a +I (electron-releasing) effect, increasing electron density on the nitrogen atom and making the lone pair more readily available for donation.
How can you distinguish between primary, secondary, and tertiary amines?
They can be distinguished using the Hinsberg test (benzene sulphonyl chloride), where primary amines form a soluble alkali salt, secondary amines form an insoluble precipitate, and tertiary amines do not react.
Why cannot aromatic primary amines be prepared by Gabriel phthalimide synthesis?
Aryl halides do not undergo nucleophilic substitution with the anion formed by phthalimide under ordinary conditions because of the partial double bond character of the carbon-chlorine bond.
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