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Class 12 Science (PCM)

Chemistry Part 2

Amines

Amines

Action PlanNotesQuestionsMock-Test
Study Action Plan (Sorted by Difficulty)
Importance of Diazonium Salts in Aromatic Synthesis
Accuracy: 0%
Total Attempted0
Total Correct0
Total Incorrect0
Difficulty Level:
High
Amine Salt Formation and Separation
Accuracy: 40%
Total Attempted5
Total Correct2
Total Incorrect3
Difficulty Level:
High
Diazonium Salt Preparation and Stability
Accuracy: 42%
Total Attempted12
Total Correct5
Total Incorrect7
Difficulty Level:
High
Basicity of Amines
Accuracy: 48%
Total Attempted23
Total Correct11
Total Incorrect12
Difficulty Level:
High
Preparation of Amines
Accuracy: 50%
Total Attempted14
Total Correct7
Total Incorrect7
Difficulty Level:
Medium
Reactions of Amines
Accuracy: 50%
Total Attempted26
Total Correct13
Total Incorrect13
Difficulty Level:
Medium
Protection of Amino Group by Acetylation
Accuracy: 54%
Total Attempted13
Total Correct7
Total Incorrect6
Difficulty Level:
Medium
Hinsberg Test for 1°, 2° and 3° Amines
Accuracy: 58%
Total Attempted12
Total Correct7
Total Incorrect5
Difficulty Level:
Medium
Diazonium Salts
Accuracy: 60%
Total Attempted20
Total Correct12
Total Incorrect8
Difficulty Level:
Medium
Electrophilic Substitution in Aniline
Accuracy: 60%
Total Attempted10
Total Correct6
Total Incorrect4
Difficulty Level:
Medium
Displacement Reactions of Diazonium Salts
Accuracy: 64%
Total Attempted22
Total Correct14
Total Incorrect8
Difficulty Level:
Medium
Ammonolysis and Alkylation of Amines
Accuracy: 66%
Total Attempted29
Total Correct19
Total Incorrect10
Difficulty Level:
Medium
Coupling Reactions of Diazonium Salts
Accuracy: 67%
Total Attempted9
Total Correct6
Total Incorrect3
Difficulty Level:
Medium
Physical Properties of Amines
Accuracy: 68%
Total Attempted19
Total Correct13
Total Incorrect6
Difficulty Level:
Medium
Nitrous Acid Reactions of Amines
Accuracy: 69%
Total Attempted16
Total Correct11
Total Incorrect5
Difficulty Level:
Medium
Acylation and Benzoylation of Amines
Accuracy: 69%
Total Attempted13
Total Correct9
Total Incorrect4
Difficulty Level:
Medium
Gabriel Phthalimide and Hoffmann Bromamide Reactions
Accuracy: 74%
Total Attempted27
Total Correct20
Total Incorrect7
Difficulty Level:
Medium
Nomenclature of Amines
Accuracy: 77%
Total Attempted13
Total Correct10
Total Incorrect3
Difficulty Level:
Low
Structure and Classification of Amines
Accuracy: 78%
Total Attempted9
Total Correct7
Total Incorrect2
Difficulty Level:
Low
Carbylamine Reaction
Accuracy: 100%
Total Attempted3
Total Correct3
Total Incorrect0
Difficulty Level:
Low

Learning Objectives

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Learning Objectives

  • Describe amines as derivatives of ammonia having a pyramidal structure.
  • Classify amines as primary, secondary, and tertiary.
  • Name amines using common names and the IUPAC system.
  • Describe some important methods of preparation of amines.
  • Explain the properties of amines.
  • Distinguish between primary, secondary, and tertiary amines.
  • Describe the method of preparation of diazonium salts and their importance in the synthesis of aromatic compounds including azo dyes.

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Revision Notes & Summary

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Notes on Amines

1. Classification of Amines

  • Primary Amines (1°): One hydrogen atom of ammonia is replaced by an alkyl or aryl group (RNH₂).
  • Secondary Amines (2°): Two hydrogen atoms are replaced (R-NHR').
  • Tertiary Amines (3°): All three hydrogen atoms are replaced (R-NR'R'').
  • Simple vs Mixed Amines: Simple amines have identical groups, while mixed amines have different groups.

2. Structure of Amines

  • Geometry: Nitrogen in amines is sp³ hybridized, leading to a pyramidal structure.
  • Bond Angles: The bond angle C-N-E is less than 109.5°, typically around 108° in trimethylamine.

3. Physical Properties

  • State: Lower aliphatic amines are gases; primary amines with three or more carbons are liquids; higher amines are solids.
  • Solubility: Lower aliphatic amines are soluble in water due to hydrogen bonding; solubility decreases with increasing molecular mass.
  • Boiling Points: Primary amines have higher boiling points than secondary and tertiary amines due to stronger hydrogen bonding.

4. Preparation of Amines

  1. Reduction of Nitro Compounds: Nitro compounds can be reduced to amines using hydrogen gas in the presence of catalysts like nickel or palladium.
    • Example:
      • NO₂ → NH₂ (using H₂/Pd)
  2. Ammonolysis of Alkyl Halides: Alkyl halides react with ammonia to form amines.
    • Example:
      • R-X + NH₃ → R-NH₃X (substituted ammonium salt)

5. Reactions of Amines

  • Acid-Base Reactions: Amines can act as bases and react with acids to form ammonium salts.
  • Diazotization: Aromatic amines can be converted to diazonium salts, which are useful intermediates in organic synthesis.

6. Key Reactions and Conversions

  • Hofmann Bromamide Reaction: Converts amides to primary amines.
  • Carbylamine Reaction: Used to identify primary amines by producing a foul-smelling gas.
  • Coupling Reaction: Diazotized amines can couple with phenols to form azo dyes.

7. Important Concepts

  • Basicity: Aliphatic amines are generally stronger bases than aromatic amines due to the electron-donating effect of alkyl groups.
  • Acidity: Amines are less acidic than alcohols of comparable molecular mass due to the presence of the unshared pair of electrons on nitrogen.

8. Common Mistakes and Tips

  • Identifying Amines: Use p-toluenesulphonyl chloride for distinguishing between primary, secondary, and tertiary amines.
  • Reactivity: Remember that the presence of an amino group in an aromatic ring enhances reactivity compared to aliphatic amines.
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Practice Test – MCQs, True/False

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Multiple Choice Questions

A.

pp-Hydroxyazobenzene

B.

pp-Aminoazobenzene

C.

Benzenediazonium chloride

D.

Aniline
Correct Answer: A

Solution:

Diazonium salts couple with phenols through electrophilic substitution to form azo compounds such as pp-hydroxyazobenzene.

Chapter Concept:

Coupling Reactions of Diazonium Salts

A.

Hydroxide ion (OH−OH^-)

B.

Iodide ion (I−I^-)

C.

Cyanide ion (CN−CN^-)

D.

Fluoride ion (F−F^-)
Correct Answer: C

Solution:

In the Sandmeyer reaction, the diazonium group is replaced by Cl−Cl^-, Br−Br^-, or CN−CN^- ions in the presence of copper(I) salts.

Chapter Concept:

Displacement Reactions of Diazonium Salts

A.

Hinsberg reaction

B.

Carbylamine reaction

C.

Acylation

D.

Electrophilic substitution
Correct Answer: B

Solution:

The carbylamine reaction is used to test for primary amines as it forms foul-smelling isocyanides.

Chapter Concept:

Reactions of Amines

A.

Sandmeyer reaction

B.

Gabriel synthesis

C.

Hofmann bromamide reaction

D.

Friedel-Crafts reaction
Correct Answer: A

Solution:

The Sandmeyer reaction is used to replace the diazonium group with halide ions such as Cl−Cl^-, Br−Br^-, or CN−CN^-.

Chapter Concept:

Diazonium Salts

A.

2,4,6-tribromoaniline

B.

2-bromoaniline

C.

4-bromoaniline

D.

3-bromoaniline
Correct Answer: A

Solution:

Aniline reacts with bromine water to give 2,4,6-tribromoaniline as the major product due to the strong activating effect of the -NH_2 group, which directs substitution to the ortho and para positions.

Chapter Concept:

Electrophilic Substitution in Aniline

A.

Ammonolysis of alkyl halides produces only primary amines.

B.

Ammonolysis of alkyl halides can lead to the formation of secondary, tertiary amines, and quaternary ammonium salts.

C.

Ammonolysis of alkyl halides is carried out at room temperature.

D.

Ammonolysis of alkyl halides favors the formation of tertiary amines when excess ammonia is used.
Correct Answer: B

Solution:

Ammonolysis of alkyl halides involves nucleophilic substitution where the halogen is replaced by an amino group, leading to the formation of primary, secondary, tertiary amines, and quaternary ammonium salts.

Chapter Concept:

Ammonolysis and Alkylation of Amines

A.

Benzamide

B.

N-Phenylethanamide

C.

N-Methylbenzamide

D.

N,N-Dimethylaniline
Correct Answer: B

Solution:

When aniline reacts with benzoyl chloride in the presence of pyridine, the major product is N-Phenylethanamide, also known as acetanilide.

Chapter Concept:

Acylation and Benzoylation of Amines

A.

Nitration

B.

Sulphonation

C.

Bromination with bromine water

D.

Friedel-Crafts alkylation
Correct Answer: C

Solution:

Aniline reacts with bromine water to give 2,4,6-tribromoaniline as the product.

Chapter Concept:

Electrophilic Substitution in Aniline

A.

Phenol

B.

Benzenediazonium chloride

C.

Aniline hydrochloride

D.

Azobenzene
Correct Answer: B

Solution:

Aromatic amines like aniline react with nitrous acid at low temperatures (273-278 K) to form stable diazonium salts, such as benzenediazonium chloride.

Chapter Concept:

Nitrous Acid Reactions of Amines

A.

Primary amines have more hydrogen atoms available for hydrogen bonding.

B.

Tertiary amines have stronger van der Waals forces.

C.

Primary amines have larger molecular weights.

D.

Tertiary amines form stronger ionic bonds.
Correct Answer: A

Solution:

Primary amines have two hydrogen atoms available for hydrogen bonding, whereas tertiary amines lack hydrogen atoms bonded to nitrogen, reducing their ability to engage in hydrogen bonding.

Chapter Concept:

Physical Properties of Amines

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True or False

Correct Answer: False

Solution:

Gabriel phthalimide synthesis cannot be used to prepare aromatic primary amines because aryl halides do not undergo nucleophilic substitution with the anion formed by phthalimide.

Chapter Concept :

Preparation of Amines

Correct Answer: True

Solution:

Diazonium salts undergo coupling reactions with phenols and anilines through electrophilic substitution to form azo compounds such as pp-hydroxyazobenzene and pp-aminoazobenzene. These compounds have extended conjugation, making them suitable as dyes.

Chapter Concept :

Coupling Reactions of Diazonium Salts

Correct Answer: False

Solution:

Benzenediazonium chloride is stable only at low temperatures (273–278 K) and decomposes easily at higher temperatures. It is not stored for long periods and is used immediately after preparation.

Chapter Concept :

Diazonium Salt Preparation and Stability

Correct Answer: False

Solution:

The carbylamine reaction is specific to primary amines, both aliphatic and aromatic, and does not occur with secondary or tertiary amines.

Chapter Concept :

Carbylamine Reaction

Correct Answer: True

Solution:

Lower aliphatic amines are indeed gases with a fishy odour and are soluble in water because they can form hydrogen bonds with water molecules.

Chapter Concept :

Physical Properties of Amines

Correct Answer: False

Solution:

Primary aliphatic amines react with nitrous acid to form aliphatic diazonium salts, which are unstable and decompose to liberate N2N_2 gas and form alcohols.

Chapter Concept :

Nitrous Acid Reactions of Amines

Correct Answer: True

Solution:

Ammonolysis of alkyl halides involves the nucleophilic substitution of the halogen atom by an amino group. Using a large excess of ammonia favors the formation of primary amine as the major product.

Chapter Concept :

Ammonolysis and Alkylation of Amines

Correct Answer: True

Solution:

Acetylation converts aniline to acetanilide, which decreases the electron donation from the nitrogen atom, thus controlling the reactivity and allowing for selective monosubstitution.

Chapter Concept :

Protection of Amino Group by Acetylation

Correct Answer: True

Solution:

According to the IUPAC nomenclature, primary amines are named by replacing the 'e' in alkane with 'amine', as stated in the text.

Chapter Concept :

Nomenclature of Amines

Correct Answer: False

Solution:

Aromatic amines are weaker bases than aliphatic amines because the lone pair on the nitrogen is delocalized into the aromatic ring, reducing its availability for protonation.

Chapter Concept :

Basicity of Amines

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