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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.

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 reaction

D.

Bromination reaction
Correct Answer: B

Solution:

The carbylamine reaction is used to test for primary amines. It involves heating the amine with chloroform and alcoholic KOHKOH, resulting in the formation of isocyanides (carbylamines), which have a foul smell.

Chapter Concept:

Reactions of Amines

A.

C6H5NH2C_6H_5NH_2 (Aniline)

B.

(C2H5)2NH(C_2H_5)_2NH (Diethylamine)

C.

(CH3)3N(CH_3)_3N (Trimethylamine)

D.

C6H5N(CH3)2C_6H_5N(CH_3)_2 (N,N-Dimethylaniline)
Correct Answer: A

Solution:

Aniline (C6H5NH2C_6H_5NH_2) is a primary amine because it has one alkyl or aryl group attached to the nitrogen atom.

Chapter Concept:

Structure and Classification of Amines

A.

Secondary amines form diazonium salts.

B.

Secondary amines form nitrosoamines.

C.

Secondary amines liberate N2N_2 gas.

D.

Secondary amines undergo no reaction.
Correct Answer: B

Solution:

Secondary amines react with nitrous acid to form nitrosoamines, not diazonium salts or N2N_2 gas.

Chapter Concept:

Nitrous Acid Reactions of Amines

A.

Conversion of amides to nitriles.

B.

Conversion of amides to primary amines with one carbon less.

C.

Conversion of amides to secondary amines.

D.

Conversion of amides to carboxylic acids.
Correct Answer: B

Solution:

The Hoffmann bromamide degradation reaction converts amides into primary amines with one carbon less via the use of bromine and sodium or potassium hydroxide.

Chapter Concept:

Gabriel Phthalimide and Hoffmann Bromamide Reactions

A.

It acts as a catalyst.

B.

It acts as a solvent.

C.

It acts as a base to remove HClHCl.

D.

It acts as an oxidizing agent.
Correct Answer: C

Solution:

Pyridine acts as a base to remove HClHCl formed during the acetylation of aniline, thereby shifting the equilibrium to the right and facilitating the reaction.

Chapter Concept:

Protection of Amino Group by Acetylation

A.

Benzene

B.

Phenol

C.

Aniline

D.

Nitrobenzene
Correct Answer: A

Solution:

When benzenediazonium chloride is treated with hypophosphorous acid, it reduces to benzene with the release of nitrogen gas.

Chapter Concept:

Diazonium Salts

A.

RN2XRN_2X

B.

R2N2XR_2N_2X

C.

R3N2XR_3N_2X

D.

R2N3XR_2N_3X
Correct Answer: A

Solution:

The general formula for diazonium salts is RN2XRN_2X, where RR is an aryl group and XX is an anion.

Chapter Concept:

Diazonium Salts

A.

To increase the electron donation from nitrogen

B.

To control the high activating effect of the −NH2-NH_2 group

C.

To enhance the basicity of the amine

D.

To prevent the formation of diazonium salts
Correct Answer: B

Solution:

Acetylation reduces the electron donation from nitrogen, allowing controlled monosubstitution, which is crucial for protecting the amino group during reactions.

Chapter Concept:

Protection of Amino Group by Acetylation

A.

Aniline

B.

Benzenamine

C.

Phenylamine

D.

Aminobenzene
Correct Answer: B

Solution:

The IUPAC name for C6H5NH2C_6H_5NH_2 is Benzenamine. Aniline is the common name, but in IUPAC nomenclature, the suffix 'amine' is added to the name of the parent hydrocarbon, benzene.

Chapter Concept:

Nomenclature of Amines

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True or False

Correct Answer: True

Solution:

Amines are classified into primary (1°), secondary (2°), and tertiary (3°) based on the number of hydrogen atoms replaced by alkyl or aryl groups in the ammonia molecule.

Chapter Concept :

Structure and Classification of Amines

Correct Answer: True

Solution:

Amines have a pyramidal structure because the nitrogen atom is sp3sp^3 hybridized, leading to a geometry similar to ammonia, with one lone pair of electrons.

Chapter Concept :

Structure and Classification of Amines

Correct Answer: False

Solution:

Aromatic amines are weaker bases than aliphatic amines because the lone pair on nitrogen is delocalized due to resonance with the aromatic ring, making it less available for protonation.

Chapter Concept :

Basicity of Amines

Correct Answer: True

Solution:

Primary and secondary amines react with benzoyl chloride in the presence of a base such as pyridine to form amides. The base helps in removing the HClHCl formed during the reaction, shifting the equilibrium towards the formation of the amide.

Chapter Concept :

Acylation and Benzoylation of Amines

Correct Answer: True

Solution:

The boiling point order of isomeric amines is indeed 1° > 2° > 3° because primary amines have two hydrogen atoms available for hydrogen bonding, leading to stronger intermolecular forces compared to secondary and tertiary amines.

Chapter Concept :

Physical Properties of Amines

Correct Answer: True

Solution:

Primary amines react with benzenesulphonyl chloride to form sulphonamides which are soluble in alkali due to the acidic hydrogen present in the sulphonamide group.

Chapter Concept :

Hinsberg Test for 1°, 2° and 3° Amines

Correct Answer: False

Solution:

Diazonium salts are generally unstable at high temperatures and are typically used immediately after preparation. They are stable only for a short time in solution at low temperatures (273-278 K).

Chapter Concept :

Diazonium Salts

Correct Answer: False

Solution:

Gabriel phthalimide synthesis is not suitable for preparing aromatic primary amines because aryl halides do not undergo nucleophilic substitution with the anion formed by phthalimide.

Chapter Concept :

Reactions of Amines

Correct Answer: True

Solution:

The carbylamine reaction is a test for primary amines where they react with chloroform and ethanolic potassium hydroxide to form isocyanides, which are foul-smelling substances.

Chapter Concept :

Reactions of Amines

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

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