CBSE Class 12 Chemistry (2026–27)
Chapter 10: Amines
20 Important Questions and Answers
These questions cover the most important topics of the Amines chapter, including classification, preparation, basicity, reactions, diazotisation, and distinguishing tests that are frequently asked in CBSE examinations.
1. What are amines? How are they classified?
Answer:
Amines are organic compounds derived from ammonia (NH₃) by replacing one or more hydrogen atoms with alkyl or aryl groups. Depending on the number of hydrogen atoms replaced, amines are classified into primary (1°), secondary (2°), and tertiary (3°) amines. In primary amines, one hydrogen is replaced (RNH₂); in secondary amines, two hydrogens are replaced (R₂NH); and in tertiary amines, all three hydrogens are replaced (R₃N). Amines may also be classified as aliphatic or aromatic depending on whether the amino group is attached to an alkyl or aryl group. This classification helps predict their physical and chemical properties and reactions.
2. Why are amines basic in nature?
Answer:
Amines are basic because the nitrogen atom contains a lone pair of electrons. This lone pair can accept a proton (H⁺) from acids, making amines proton acceptors according to the Bronsted–Lowry concept. When amines react with acids, they form ammonium salts. The basicity depends on the availability of the lone pair. Electron-donating alkyl groups increase electron density on nitrogen and generally increase basicity, whereas resonance in aromatic amines like aniline decreases the availability of the lone pair, reducing basicity. Therefore, aliphatic amines are generally more basic than aromatic amines. Understanding basicity trends is important for solving reaction and reasoning-based questions.
3. Explain Gabriel Phthalimide Synthesis.
Answer:
Gabriel Phthalimide Synthesis is an important method used for preparing pure primary aliphatic amines. In this process, phthalimide is first converted into potassium phthalimide, which reacts with an alkyl halide through nucleophilic substitution. The resulting N-alkyl phthalimide is then hydrolysed to produce the corresponding primary amine. This method is useful because it avoids the formation of secondary and tertiary amines. However, it cannot be used for preparing aromatic amines since aryl halides do not undergo nucleophilic substitution easily. Gabriel synthesis is a common board examination topic and is often asked in reaction-based questions.
4. What is Hofmann Bromamide Reaction?
Answer:
Hofmann Bromamide Reaction, also called Hofmann degradation, is a method for preparing primary amines from amides. In this reaction, an amide is treated with bromine and potassium hydroxide. The amide loses the carbonyl carbon atom and forms a primary amine containing one carbon atom less than the original amide. For example, ethanamide produces methylamine. This reaction is important because it provides a convenient route for obtaining amines with a shorter carbon chain. The reaction is widely used in organic synthesis and is frequently included in CBSE board examinations as a named reaction requiring explanation and equation writing.
5. Why is aniline less basic than ethylamine?
Answer:
Aniline is less basic than ethylamine because the lone pair of electrons on the nitrogen atom in aniline participates in resonance with the benzene ring. Due to this delocalisation, the lone pair becomes less available for protonation. In ethylamine, the alkyl group exerts a positive inductive effect (+I), increasing electron density on nitrogen and making the lone pair more available for accepting a proton. As a result, ethylamine behaves as a stronger base than aniline. This difference in basicity is a frequently asked conceptual question and helps explain the influence of resonance and inductive effects on chemical behaviour.
6. What is the Carbylamine Reaction?
Answer:
The Carbylamine Reaction is a characteristic test for primary amines. When a primary amine is heated with chloroform and alcoholic potassium hydroxide, it forms an isocyanide or carbylamine having an unpleasant smell. Secondary and tertiary amines do not give this reaction. Therefore, it is used to distinguish primary amines from other classes of amines. The reaction is important in qualitative analysis and laboratory identification of amines. In board examinations, students are often asked to write the reaction, explain its significance, or identify the class of amines that responds positively to this test.
7. What is Hinsberg’s Test?
Answer:
Hinsberg’s Test is used to distinguish primary, secondary, and tertiary amines. The amine is treated with benzenesulphonyl chloride in the presence of alkali. Primary amines form soluble sulphonamides due to the presence of an acidic hydrogen atom. Secondary amines form insoluble sulphonamides because they lack an acidic hydrogen. Tertiary amines do not react with the reagent under these conditions. This difference in behaviour allows identification of the type of amine present. Hinsberg’s Test is a standard laboratory method and an important examination topic because it combines concepts of reactivity, structure, and functional group identification.
8. What is diazotisation?
Answer:
Diazotisation is the process of converting a primary aromatic amine into a diazonium salt by treating it with nitrous acid at low temperature (273–278 K). Aniline reacts with sodium nitrite and hydrochloric acid to form benzene diazonium chloride. The reaction must be carried out at low temperature because diazonium salts are unstable at higher temperatures. Diazotisation is important because diazonium salts act as versatile intermediates in organic synthesis and can be converted into various aromatic compounds. Questions related to diazotisation frequently appear in board examinations because of its industrial and synthetic significance.
9. Why are diazonium salts important in organic synthesis?
Answer:
Diazonium salts are highly valuable intermediates because the diazonium group can be replaced by many other functional groups. Through suitable reactions, chlorine, bromine, iodine, fluorine, hydroxyl, and cyano groups can be introduced into the aromatic ring. Such transformations are difficult to achieve directly. Therefore, diazonium salts serve as key intermediates in the preparation of dyes, pharmaceuticals, and aromatic compounds. Their versatility makes them an important topic in organic chemistry. Board examinations often include questions regarding their preparation, reactions, and applications in synthetic chemistry.
10. What is the Sandmeyer Reaction?
Answer:
The Sandmeyer Reaction involves the replacement of the diazonium group in an aryl diazonium salt by chlorine, bromine, or cyanide using cuprous salts. For example, benzene diazonium chloride reacts with cuprous chloride to form chlorobenzene. This reaction is important because it allows the preparation of substituted aromatic compounds that cannot be obtained easily by direct substitution. The reaction is widely used in organic synthesis and serves as a useful method for introducing different functional groups into benzene derivatives. It is one of the most important named reactions from the Amines chapter.
11. Differentiate between aliphatic and aromatic amines.
Answer:
Aliphatic amines contain the amino group attached to an alkyl group, whereas aromatic amines contain the amino group attached directly to an aromatic ring. Examples include methylamine and aniline respectively. Aliphatic amines are generally more basic because alkyl groups donate electrons to nitrogen through the inductive effect. Aromatic amines are less basic because the lone pair on nitrogen is delocalised into the aromatic ring by resonance. Their chemical behaviour also differs in electrophilic substitution and diazotisation reactions. Understanding these differences is important for predicting reactivity and solving conceptual questions in board examinations.
12. Why do lower amines dissolve in water?
Answer:
Lower amines are soluble in water because they can form hydrogen bonds with water molecules. The nitrogen atom possesses a lone pair of electrons that interacts with hydrogen atoms of water. This hydrogen bonding facilitates dissolution. As the carbon chain length increases, the hydrophobic hydrocarbon portion becomes larger, reducing solubility. Therefore, lower amines such as methylamine and ethylamine are highly soluble in water, while higher amines become less soluble. The solubility behaviour of amines is often compared with alcohols and is a common theory question in CBSE examinations.
13. What is acylation of amines?
Answer:
Acylation is the reaction in which an amine reacts with an acid chloride or acid anhydride to form an amide. During the reaction, a hydrogen atom attached to nitrogen is replaced by an acyl group. Primary and secondary amines undergo acylation readily, whereas tertiary amines do not because they lack a replaceable hydrogen atom on nitrogen. Acylation is useful in protecting amino groups during organic synthesis and reducing the basicity of amines. It is an important reaction that demonstrates the nucleophilic nature of the amino group and is frequently asked in board examinations.
14. How are amines prepared by reduction of nitro compounds?
Answer:
Amines can be prepared by reducing nitro compounds using reducing agents such as hydrogen in the presence of a catalyst, tin and hydrochloric acid, or iron and hydrochloric acid. For example, nitrobenzene is reduced to aniline. During reduction, the nitro group (–NO₂) gains hydrogen and converts into an amino group (–NH₂). This method is particularly important for the preparation of aromatic amines. It is widely used in laboratories and industries because nitro compounds are readily available. Questions involving reaction sequences and conversions often use this preparation method as an important step.
15. Explain the reaction of amines with nitrous acid.
Answer:
The reaction of amines with nitrous acid varies according to the type of amine. Primary aliphatic amines form unstable diazonium salts that decompose to give alcohols and nitrogen gas. Primary aromatic amines form stable diazonium salts at low temperatures. Secondary amines produce nitrosoamines, while tertiary amines generally form salts without nitrogen evolution. These differences help distinguish between various classes of amines. The reaction is important both for identification and for preparing diazonium salts used in synthesis. It is commonly included in board examination questions involving reasoning and reaction mechanisms.
16. Why is aniline ortho- and para-directing?
Answer:
In aniline, the amino group donates electrons to the benzene ring through resonance. This increases electron density at the ortho and para positions, making them more reactive toward electrophilic substitution reactions. As a result, incoming electrophiles preferentially attack these positions. Therefore, aniline behaves as an ortho- and para-directing group. The activating effect of the amino group makes aniline more reactive than benzene in electrophilic substitution reactions such as bromination and nitration. Understanding directing effects is important for predicting reaction products in aromatic chemistry and frequently appears in CBSE examinations.
17. What are azo dyes?
Answer:
Azo dyes are coloured compounds containing the azo group (–N=N–) linking two aromatic rings. They are prepared through coupling reactions involving diazonium salts and aromatic compounds such as phenols or aromatic amines. Azo dyes exhibit bright colours due to extensive conjugation in their molecular structure. They are widely used in textile, paper, leather, and food industries. The preparation of azo dyes demonstrates the synthetic importance of diazonium salts. Questions regarding their formation and applications are often asked in examinations because they connect organic chemistry with industrial uses.
18. Why do tertiary amines not undergo acylation?
Answer:
Tertiary amines do not undergo acylation because the nitrogen atom does not possess any hydrogen atom attached to it. Acylation involves the replacement of a hydrogen atom bonded to nitrogen by an acyl group. Since tertiary amines contain three alkyl or aryl groups attached to nitrogen, no replaceable hydrogen is available. Consequently, they cannot form amides through acylation reactions. This behaviour helps distinguish tertiary amines from primary and secondary amines and is frequently used in identification and qualitative analysis problems.
19. Write the significance of the Carbylamine Test.
Answer:
The Carbylamine Test is significant because it specifically identifies primary amines. When heated with chloroform and alcoholic potassium hydroxide, primary amines produce foul-smelling isocyanides. Secondary and tertiary amines fail to respond to this test. Thus, it serves as a reliable qualitative method for distinguishing primary amines from other nitrogen-containing compounds. The test is widely used in laboratory analysis and practical chemistry. In board examinations, students are often asked to explain the reaction, identify the amines involved, and discuss its importance as a diagnostic test.
20. Compare the basic strength of methylamine, ammonia, and aniline.
Answer:
The order of basic strength is:
Methylamine > Ammonia > Aniline
Methylamine is more basic than ammonia because the methyl group donates electrons through the positive inductive effect, increasing electron density on nitrogen. Ammonia has a lone pair available for protonation but lacks electron-donating alkyl groups. Aniline is the least basic because the nitrogen lone pair is delocalised into the benzene ring through resonance, reducing its availability for accepting a proton. This order illustrates the combined influence of inductive and resonance effects on basicity. Questions based on this comparison are among the most frequently asked conceptual questions from the Amines chapter.