Amines

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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.

Detailed Notes

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

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)
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.

Exam Tips & Common Mistakes

Common Mistakes and Exam Tips for Amines

Common Pitfalls

Misclassification of Amines: Ensure to classify amines correctly as primary, secondary, or tertiary based on the number of hydrogen atoms replaced by alkyl or aryl groups.
Incorrect Naming: Be careful with IUPAC naming conventions; remember to replace 'e' in alkanes with 'amine' for primary amines.
Overlooking Reaction Conditions: Pay attention to specific conditions required for reactions, such as temperature and the presence of catalysts.
Ignoring Solubility Trends: Remember that lower aliphatic amines are generally soluble in water, while higher amines are not due to increased hydrophobic character.

Tips for Success

Practice Reaction Mechanisms: Familiarize yourself with the mechanisms of reactions involving amines, such as ammonolysis and the Hoffmann bromamide reaction.
Understand Basicity Trends: Be aware of the factors affecting the basicity of amines, such as steric hindrance and the presence of electron-withdrawing groups.
Utilize Tests for Identification: Learn the chemical tests to distinguish between primary, secondary, and tertiary amines, such as using p-toluenesulphonyl chloride.
Review Physical Properties: Keep in mind the physical properties of amines, including boiling points and solubility, as these can be tested.
Memorize Key Reactions: Make a list of key reactions involving amines, including their products and conditions, to aid in recall during exams.

Practice & Assessment

Multiple Choice Questions

Carbylamine test

Hinsberg test

Lucas test

Tollens' test

Correct Answer: B

Solution:

The Hinsberg test can distinguish between primary (methylamine) and secondary (dimethylamine) amines based on their different solubility and reactivity with sulfonyl chloride.

Oxidizing agent

Reducing agent

Acylating agent

Catalyst

Correct Answer: C

Solution:

Acetic anhydride acts as an acylating agent, introducing an acyl group into aniline to form acetanilide.

Aniline

Ethylamine

Diethylamine

Triethylamine

Correct Answer: B

Solution:

Ethylamine is more soluble in water due to its ability to form hydrogen bonds with water molecules.

NH₂

N(CH₃)₂

(C₂H₅)₂NH

C₆H₅NHCH₃

Correct Answer: A

Solution:

NH₂ is a primary amine as it has one alkyl or aryl group attached to the nitrogen.

C₆H₅NH₂

(C₂H₅)₂NH

C₆H₅N(CH₃)₂

(CH₃)₃CNH₂

Correct Answer: A

Solution:

C₆H₅NH₂ is an example of a primary amine where the nitrogen atom is bonded to one alkyl or aryl group.

Primary amines can form more hydrogen bonds with water.

Primary amines have a larger molecular size.

Tertiary amines are more volatile.

Tertiary amines react with water to form insoluble compounds.

Correct Answer: A

Solution:

Primary amines can form more hydrogen bonds with water due to the presence of two hydrogen atoms attached to the nitrogen, enhancing solubility.

Reduction with H₂/Pd

Ammonolysis

Gabriel phthalimide synthesis

Hofmann's bromamide reaction

Correct Answer: A

Solution:

Nitromethane can be reduced to dimethylamine using hydrogen gas in the presence of a palladium catalyst.

2,4,6-tribromoaniline

Benzamide

Aniline

Benzylamine

Correct Answer: A

Solution:

The reaction of C₆H₅NH₂ with Br₂ (aq) forms 2,4,6-tribromoaniline.

Reaction with nitrous acid

Reaction with bromine water

Reaction with Grignard reagent

Reaction with acetic anhydride

Correct Answer: A

Solution:

Primary amines react with nitrous acid to form diazonium salts, which can further decompose to release nitrogen gas, while secondary amines form N-nitrosoamines.

Aromatic amines are stronger bases than aliphatic amines.

Aliphatic amines are stronger bases than aromatic amines.

Primary amines are weaker bases than tertiary amines.

Secondary amines are weaker bases than primary amines.

Correct Answer: B

Solution:

Aliphatic amines are stronger bases than aromatic amines due to the electron-releasing alkyl groups that increase electron density on the nitrogen.

Friedel-Crafts acylation

Hofmann elimination

Reduction using Fe/HCl

Diazotization

Correct Answer: C

Solution:

Nitrobenzene is reduced to aniline using Fe/HCl, which is a common method for reducing nitro groups to amines.

Ethylamine

Diethylamine

Triethylamine

Tetraethylammonium hydroxide

Correct Answer: D

Solution:

The Hofmann elimination reaction occurs with quaternary ammonium hydroxides, such as tetraethylammonium hydroxide, to form alkenes.

(CH₃)₂NH < C₂H₅NH₂ < C₂H₅OH

C₂H₅NH₂ < (CH₃)₂NH < C₂H₅OH

C₂H₅OH < C₂H₅NH₂ < (CH₃)₂NH

(CH₃)₂NH < C₂H₅OH < C₂H₅NH₂

Correct Answer: A

Solution:

The increasing order of boiling points is (CH₃)₂NH < C₂H₅NH₂ < C₂H₅OH. Alcohols generally have higher boiling points than amines due to stronger hydrogen bonding.

Quaternary ammonium iodide

Quaternary ammonium hydroxide

Secondary amine

Tertiary amine

Correct Answer: B

Solution:

The reaction sequence involves the formation of a quaternary ammonium iodide by exhaustive methylation of the aromatic amine. Subsequent treatment with silver oxide and water converts it to the quaternary ammonium hydroxide.

Phenyl isocyanide

Phenyl chloride

Aniline

Benzyl alcohol

Correct Answer: A

Solution:

The reaction of aniline (C₆H₅NH₂) with chloroform (CHCl₃) and alcoholic KOH is known as the carbylamine reaction, which produces phenyl isocyanide as the major product.

n-Butylamine (n-C₄H₉NH₂)

Diethylamine ((C₂H₅)₂NH)

Triethylamine ((C₂H₅)₃N)

Isobutylamine (C₄H₁₀NH₂)

Correct Answer: A

Solution:

n-Butylamine has the highest boiling point due to stronger hydrogen bonding compared to secondary and tertiary amines, which have less hydrogen bonding capability.

Primary amines can form more hydrogen bonds with water.

Tertiary amines have a larger molar mass.

Primary amines have a higher boiling point.

Tertiary amines are more volatile.

Correct Answer: A

Solution:

Primary amines have two hydrogen atoms capable of forming hydrogen bonds with water, increasing their solubility compared to tertiary amines, which lack hydrogen atoms for bonding.

Benzonitrile

Benzyl alcohol

Benzoic acid

Benzene

Correct Answer: C

Solution:

The reaction of C�6H�5N�2Cl with CuCN forms benzonitrile, which upon hydrolysis yields benzoic acid.

2,4,6-tribromoaniline

p-bromoaniline

m-bromoaniline

o-bromoaniline

Correct Answer: A

Solution:

Aniline reacts with bromine water to form 2,4,6-tribromoaniline due to the activating effect of the amino group.

Hoffmann bromamide reaction

Gabriel phthalimide synthesis

Friedel-Crafts acylation

Diazotization followed by hydrolysis

Correct Answer: A

Solution:

The Hoffmann bromamide reaction involves the conversion of amides to amines with one less carbon atom. Benzamide, when subjected to this reaction, forms aniline.

n-C₄H₉NH₂

(C₂H₅)₂NH

C₂H₅N(CH₃)₂

n-C₄H₉OH

Correct Answer: D

Solution:

n-C₄H₉OH has the highest boiling point due to strong hydrogen bonding compared to the amines.

n-C₄H₉NH₂

(C₂H₅)₂NH

C₂H₅N(CH₃)₂

C₂H₅CH(CH₃)₂

Correct Answer: A

Solution:

n-C₄H₉NH₂ has the highest boiling point due to stronger hydrogen bonding compared to secondary and tertiary amines.

C₆H₅NH₂

(C₂H₅)₂NH

C₂H₅NH₂

(CH₃)₃N

Correct Answer: C

Solution:

C₂H₅NH₂ will have the highest solubility in water due to its ability to form hydrogen bonds with water molecules, and it has a smaller hydrophobic alkyl group compared to the others.

Hoffmann bromamide reaction

Gabriel phthalimide synthesis

Diazotisation

Ammonolysis

Correct Answer: A

Solution:

The Hoffmann bromamide reaction is used to convert benzamide to aniline.

Aliphatic amines have more electron-donating alkyl groups.

Aromatic amines have resonance stabilization.

Aliphatic amines are less sterically hindered.

Aromatic amines have higher molecular weights.

Correct Answer: A

Solution:

Aliphatic amines are stronger bases because the electron-donating alkyl groups increase the electron density on the nitrogen, enhancing its ability to donate electrons.

N,N-Dimethylmethanamine

2-Aminopropane

Isopropylamine

Propylamine

Correct Answer: B

Solution:

The IUPAC name for (CH₃)₂CHNH₂ is 2-Aminopropane, as it is a primary amine with the amino group on the second carbon of propane.

Due to resonance stabilization of the lone pair on nitrogen in aromatic amines.

Due to the electron-withdrawing nature of the aromatic ring.

Due to steric hindrance in aromatic amines.

Due to the presence of additional hydrogen bonding in aromatic amines.

Correct Answer: A

Solution:

In aromatic amines, the lone pair on nitrogen is involved in resonance with the aromatic ring, decreasing its availability to accept protons, making them weaker bases compared to aliphatic amines.

Aniline

Benzamide

Benzene

Phenol

Correct Answer: A

Solution:

Aniline (C₆H₅NH₂) reacts with Br₂ and KOH to form a compound with molecular formula C₆H₇N.

Aniline + Br₂ (aq)

Aniline + CHCl₃ + alc.KOH

Aniline + (CH₃CO)₂O

Aniline + C₂H₅OH

Correct Answer: A

Solution:

The reaction of aniline with aqueous bromine (Br₂) leads to the formation of 2,4,6-tribromoaniline due to the high reactivity of the amino group directing bromination to the ortho and para positions.

Due to resonance stabilization in aromatic amines

Aromatic amines have higher molecular weight

Aromatic amines are more soluble in water

Aromatic amines have higher boiling points

Correct Answer: A

Solution:

Aromatic primary amines are less basic because the lone pair of electrons on the nitrogen is delocalized into the aromatic ring, reducing its availability to accept protons.

Higher amines are more soluble in water than lower amines.

Amines are insoluble in water.

Lower aliphatic amines are soluble in water due to hydrogen bonding.

Amines are more soluble in water than alcohols.

Correct Answer: C

Solution:

Lower aliphatic amines are soluble in water because they can form hydrogen bonds with water molecules.

p-Bromoaniline

2,4,6-Tribromoaniline

m-Bromoaniline

Benzylamine

Correct Answer: B

Solution:

When aniline is treated with bromine water, it undergoes bromination to form 2,4,6-tribromoaniline due to the activating effect of the amino group.

C₆H₅NC

C₆H₅NCO

C₆H₅NHCH₃

C₆H₅NH₂Cl

Correct Answer: A

Solution:

The reaction of C₆H₅NH₂ with CHCl₃ and alc.KOH produces phenyl isocyanide (C₆H₅NC).

Primary amines have more hydrogen atoms available for hydrogen bonding.

Tertiary amines have a larger molecular size.

Primary amines can form more hydrogen bonds due to their linear structure.

Tertiary amines are more polar than primary amines.

Correct Answer: A

Solution:

Primary amines have two hydrogen atoms attached to the nitrogen, allowing for more extensive hydrogen bonding compared to tertiary amines, which lack hydrogen atoms bonded to nitrogen.

n-C₄H₉NH₂

(C₂H₅)₂NH

C₂H₅N(CH₃)₂

n-C₄H₉OH

Correct Answer: D

Solution:

n-C₄H₉OH (butanol) will have the highest boiling point due to the presence of stronger hydrogen bonding compared to amines, which have weaker hydrogen bonding.

Aromatic amines reacting with chloroform and alcoholic KOH to form isocyanides.

Reduction of nitrobenzene to aniline.

Conversion of benzamide to aniline using bromine and KOH.

Acylation of aniline with acetic anhydride.

Correct Answer: A

Solution:

The Carbylamine reaction involves the reaction of primary amines with chloroform and alcoholic KOH to form isocyanides, which have a characteristic foul smell.

C₆H₅NH₂

C₂H₅NH₂

(C₂H₅)₂NH

NH₃

Correct Answer: C

Solution:

Diethylamine ((C₂H₅)₂NH) is a stronger base than the other options due to the electron-releasing effect of the ethyl groups.

Aromatic amines are too reactive to be formed in this reaction.

The aromatic ring deactivates the nucleophilic substitution needed for the reaction.

The reaction conditions are too harsh for aromatic compounds.

The phthalimide cannot be easily removed from the aromatic amine.

Correct Answer: B

Solution:

The Gabriel Phthalimide Synthesis is not suitable for aromatic primary amines because the aromatic ring deactivates the nucleophilic substitution required for the reaction.

Aniline

Ethylamine

Methylamine

Propylamine

Correct Answer: A

Solution:

Aniline cannot be prepared by Gabriel phthalimide synthesis because it is an aromatic amine.

All amines are equally soluble in water.

Tertiary amines are more soluble than primary amines.

Primary amines are more soluble than tertiary amines.

Amines are insoluble in water.

Correct Answer: C

Solution:

Primary amines are more soluble in water than tertiary amines due to their ability to form more hydrogen bonds with water molecules.

C₆H₅NH₂

(C₂H₅)₂NH

C₂H₅NH₂

C₆H₅N(CH₃)₂

Correct Answer: C

Solution:

C₂H₅NH₂ (ethylamine) is most soluble in water due to its ability to form hydrogen bonds with water molecules, and its small size compared to aromatic amines.

CH₃NH₂

(C₂H₅)₂NH

C₆H₅NH₂

NH₃

Correct Answer: B

Solution:

(C₂H₅)₂NH is a secondary amine because it has two alkyl groups attached to the nitrogen.

Reduction of nitrobenzene with Fe/HCl

Gabriel phthalimide synthesis

Reduction of benzonitrile with LiAlH₄

Ammonolysis of benzyl chloride

Correct Answer: B

Solution:

Gabriel phthalimide synthesis cannot be used to prepare aromatic primary amines due to the inability of the phthalimide ion to attack the aromatic ring.

Acetanilide

Aniline acetate

N-Phenylacetamide

N-Methylacetanilide

Correct Answer: A

Solution:

When aniline is treated with acetic anhydride, it undergoes acylation to form acetanilide, which is an amide.

Aromatic amines are too reactive and decompose.

The reaction conditions are not suitable for aromatic rings.

Aromatic amines do not form stable intermediates.

Aromatic amines are not nucleophilic enough to react.

Correct Answer: C

Solution:

Aromatic primary amines cannot be prepared by Gabriel phthalimide synthesis because the intermediates formed are not stable when aromatic rings are involved.

Ethylamine

Propylamine

Ethanol

Ethanoic acid

Correct Answer: A

Solution:

The sequence involves the conversion of ethyl bromide to propanenitrile (A) using KCN, reduction to propylamine (B) using LiAlH₄, and finally diazotization to ethylamine (C) using HNO₂ at 0°C.

Acetanilide

Aniline acetate

Phenyl acetate

Ethyl aniline

Correct Answer: A

Solution:

The reaction of aniline with acetic anhydride results in the formation of acetanilide.

Due to resonance stabilization in aromatic amines

Due to higher molecular mass

Because they are liquids

Because they have more hydrogen atoms

Correct Answer: A

Solution:

Aromatic amines are less basic due to resonance stabilization which delocalizes the lone pair of electrons on nitrogen.

Hinsberg test

Lucas test

Benedict's test

Tollens' test

Correct Answer: A

Solution:

The Hinsberg test is used to distinguish between primary, secondary, and tertiary amines based on their reaction with benzenesulfonyl chloride.

C₆H₅NH₂ + CH₃COCl

C₆H₅NH₂ + Br₂ (aq)

C₆H₅NH₂ + CHCl₃ + alc.KOH

C₆H₅NH₂ + NaNO₂ + HCl

Correct Answer: A

Solution:

The reaction of aniline (C₆H₅NH₂) with acetyl chloride (CH₃COCl) results in the formation of N-phenylethanamide through acylation.

C₆H₅NH₂

C₂H₅NH₂

(C₂H₅)₂NH

NH₃

Correct Answer: C

Solution:

(C₂H₅)₂NH is the strongest base due to the electron-donating effect of the ethyl groups.

Butanamide

Propanamide

Ethanamide

Methanamide

Correct Answer: A

Solution:

Propanamine contains three carbons, so the starting amide must have four carbon atoms, which is butanamide.

Aniline

Benzylamine

Phenylamine

Cyclohexylamine

Correct Answer: A

Solution:

Compound 'C' is aniline, which has the molecular formula C₆H₅NH₂. The reaction sequence involves the formation of aniline from an aromatic amine precursor.

Aromatic amines are too reactive.

The method is specific to aliphatic amines.

Aromatic amines decompose during the reaction.

The reaction requires a catalyst not compatible with aromatic amines.

Correct Answer: B

Solution:

Gabriel phthalimide synthesis is specific to the preparation of aliphatic primary amines.

Butan-1-amine

2-Methylpropan-1-amine

N,N-Dimethylethanamine

N-Ethylmethanamine

Correct Answer: A

Solution:

Butan-1-amine is a primary amine with the molecular formula C₄H₁₁N.

Gabriel phthalimide synthesis

Hoffmann's bromamide reaction

Ammonolysis

Diazotisation

Correct Answer: C

Solution:

Ammonolysis of alkyl halides involves the nucleophilic substitution of the halogen atom by an amino group, forming primary amines.

Ammonolysis

Acylation

Diazotisation

Coupling reaction

Correct Answer: A

Solution:

Ammonolysis of alkyl halides is used to prepare primary amines by replacing the halogen atom with an amino group.

(CH₃)₂NH < C₂H₅NH₂ < C₂H₅OH

C₂H₅NH₂ < (CH₃)₂NH < C₂H₅OH

C₂H₅OH < C₂H₅NH₂ < (CH₃)₂NH

(CH₃)₂NH < C₂H₅OH < C₂H₅NH₂

Correct Answer: A

Solution:

The boiling point order is due to the strength of hydrogen bonding: alcohols > primary amines > secondary amines.

True or False

Correct Answer: True

Solution:

n-Butylamine has a higher boiling point than diethylamine due to stronger hydrogen bonding in n-butylamine.

Correct Answer: False

Solution:

Aniline is an ortho- and para-directing group in electrophilic aromatic substitution reactions. However, due to the deactivating effect of the amino group under nitrating conditions, m-nitroaniline is not the major product.

Correct Answer: True

Solution:

The molecular geometry of a tertiary amine is trigonal pyramidal, and the bond angle is approximately 108°.

Correct Answer: True

Solution:

P-toluenesulphonyl chloride reacts differently with primary, secondary, and tertiary amines, allowing for their distinction based on the type of product formed.

Correct Answer: False

Solution:

Ethylamine is more soluble in water than aniline because ethylamine can form stronger hydrogen bonds with water due to its smaller size and less hydrophobic character.

Correct Answer: False

Solution:

Amines are less acidic than alcohols of comparable molecular masses because the nitrogen atom in amines is less electronegative than the oxygen atom in alcohols, resulting in weaker acidic properties.

Correct Answer: True

Solution:

Aniline (C₆H₅NH₂) is less basic than ethylamine (C₂H₅NH₂) due to resonance stabilization of the lone pair on the nitrogen in the aromatic ring, which reduces its availability for protonation.

Correct Answer: True

Solution:

Diazonium salts of aromatic amines are more stable due to resonance stabilization involving the aromatic ring.

Correct Answer: True

Solution:

Nitro compounds can be reduced to amines using hydrogen gas in the presence of a catalyst or by reduction with metals in an acidic medium.

Correct Answer: True

Solution:

The Gabriel phthalimide synthesis is not suitable for preparing aromatic primary amines due to the inability to form the necessary intermediates with aromatic compounds.

Correct Answer: True

Solution:

According to the excerpt, an aromatic compound 'A' on treatment with aqueous ammonia and heating forms compound 'B', which on heating with Br₂ and KOH forms a compound 'C' of molecular formula C₆H₇N.

Correct Answer: True

Solution:

Amines are classified as primary (1°), secondary (2°), and tertiary (3°) depending on how many hydrogen atoms in ammonia are replaced by alkyl or aryl groups.

Correct Answer: True

Solution:

Primary amines can form more extensive hydrogen bonds compared to tertiary amines, which lack hydrogen atoms directly bonded to nitrogen, resulting in higher boiling points.

Correct Answer: False

Solution:

Gabriel phthalimide synthesis is not suitable for preparing aromatic primary amines due to the inability of the method to introduce the aryl group.

Correct Answer: True

Solution:

Aniline reacts with bromine water to form 2,4,6-tribromoaniline due to the activating effect of the amino group, which directs bromination to the ortho and para positions.

Correct Answer: True

Solution:

Although the amino group in aniline is o- and p- directing, nitration of aniline results in a significant amount of m-nitroaniline due to the formation of a nitronium ion which can attack the meta position.

Correct Answer: True

Solution:

Aryldiazonium salts undergo nucleophilic substitution reactions, allowing the diazonium group to be replaced by nucleophiles such as halides, forming aryl halides.

Correct Answer: True

Solution:

Amines react with carboxylic acids to form salts at room temperature, as the amine acts as a base and the carboxylic acid acts as an acid.

Correct Answer: True

Solution:

In the gas phase, ethylamine is a stronger base than ammonia due to the electron-donating effect of the ethyl group, which increases the electron density on the nitrogen atom.

Correct Answer: True

Solution:

In the gas phase, the basic strength of amines increases with the number of alkyl groups due to the electron-releasing effect of alkyl groups, which increases the electron density on nitrogen.

Correct Answer: False

Solution:

The amino group is an electron-donating group, which increases the reactivity of the aromatic ring towards electrophilic substitution by activating the ring.

Correct Answer: True

Solution:

Amines are less acidic than alcohols because the nitrogen atom in amines is less electronegative than the oxygen atom in alcohols, making the N-H bond less polar than the O-H bond.

Correct Answer: True

Solution:

Aniline reacts with bromine water to give a white precipitate of 2,4,6-tribromoaniline due to the highly activating nature of the amino group.

Correct Answer: True

Solution:

In the gas phase, the basic strength of amines is influenced by the availability of the lone pair on nitrogen and the inductive effect of alkyl groups, leading to the given order.

Correct Answer: True

Solution:

P-toluenesulphonyl chloride is used for the identification of primary, secondary, and tertiary amines, including aromatic amines.

Correct Answer: False

Solution:

Aromatic primary amines cannot be prepared by Gabriel phthalimide synthesis because the method is not suitable for aromatic systems.

Correct Answer: True

Solution:

Aniline does not undergo Friedel-Crafts reaction because the amino group forms a complex with the Lewis acid catalyst, deactivating the ring.

Correct Answer: True

Solution:

Primary amines have stronger intermolecular hydrogen bonding than secondary amines because they have two hydrogen atoms available for hydrogen bond formation, leading to higher boiling points.

Correct Answer: False

Solution:

Aromatic amines are generally less basic than aliphatic amines due to resonance stabilization of the lone pair on nitrogen, which reduces its availability for protonation.

Correct Answer: True

Solution:

The solubility of amines in water decreases with increasing molar mass due to the increased size of the hydrophobic alkyl part, which reduces the ability to form hydrogen bonds with water.

Correct Answer: True

Solution:

Aryldiazonium salts, usually obtained from arylamines, can undergo coupling reactions with phenols or arylamines to form azo dyes.

Correct Answer: True

Solution:

Tertiary amines can form hydrogen bonds with water due to the presence of a lone pair of electrons on the nitrogen atom.

Correct Answer: False

Solution:

Tertiary amines cannot form intermolecular hydrogen bonds because they lack a hydrogen atom bonded to nitrogen.

Correct Answer: True

Solution:

Aliphatic amines are stronger bases than aromatic amines because the lone pair of electrons on nitrogen is more available for bonding in aliphatic amines.

Correct Answer: True

Solution:

Primary amines have higher boiling points than tertiary amines due to stronger intermolecular hydrogen bonding.

Correct Answer: True

Solution:

In the gas phase, the basic strength of amines is influenced by the availability of the lone pair of electrons on nitrogen, which is more accessible in primary and secondary amines compared to tertiary amines and ammonia.

Correct Answer: False

Solution:

The basic strength of amines generally decreases in the order: secondary > tertiary > primary, due to the electron-donating effect of alkyl groups and steric hindrance in tertiary amines.

Correct Answer: True

Solution:

The basicity of amines is determined by the availability of the lone pair of electrons on the nitrogen atom, which can accept protons.

Correct Answer: True

Solution:

The Gabriel phthalimide synthesis is not suitable for preparing aromatic primary amines due to the inability to form the necessary intermediate with aromatic substrates.

Correct Answer: True

Solution:

Primary amines have stronger intermolecular hydrogen bonding due to the presence of two hydrogen atoms, leading to higher boiling points compared to tertiary amines.

Correct Answer: True

Solution:

This is known as the carbylamine reaction, where primary amines react with chloroform and alcoholic KOH to form isocyanides (carbylamines).

Correct Answer: True

Solution:

Amines react with alkyl halides in a nucleophilic substitution reaction known as alkylation, which can lead to the formation of secondary and tertiary amines.

Correct Answer: True

Solution:

Aromatic amines react with nitrous acid to form diazonium salts, while aliphatic amines form alcohols.

Correct Answer: True

Solution:

Aryldiazonium salts undergo coupling reactions with phenols or arylamines to form azo dyes, which are characterized by their vivid colors.

Correct Answer: True

Solution:

Amines can form hydrogen bonds with water due to the presence of the nitrogen atom with a lone pair, making lower aliphatic amines soluble in water.

Correct Answer: True

Solution:

Aliphatic amines are stronger bases because the lone pair of electrons on the nitrogen is more available for donation compared to aromatic amines, where the lone pair is delocalized into the aromatic ring.

Correct Answer: True

Solution:

Aniline does not undergo the Friedel-Crafts reaction because the amino group forms a complex with the Lewis acid catalyst, deactivating the aromatic ring.

Correct Answer: True

Solution:

Aromatic amines are less basic than aliphatic amines due to the resonance stabilization of the lone pair on nitrogen in aromatic amines, which makes it less available for protonation.

Correct Answer: True

Solution:

n-Butylamine (n-C₄H₉NH₂) has a boiling point of 350.8 K, which is higher than that of diethylamine ((C₂H₅)₂NH) with a boiling point of 329.3 K.

Correct Answer: True

Solution:

Primary amines have higher boiling points than tertiary amines because primary amines can form more extensive hydrogen bonding due to the presence of two hydrogen atoms.

Correct Answer: True

Solution:

Aryldiazonium salts undergo replacement of the diazonium group with nucleophiles, making them useful for synthesizing aryl halides.

Amines

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Learning Objectives

Learning Objectives

Detailed Notes

Notes on Amines

1. Classification of Amines

2. Structure of Amines

3. Physical Properties

4. Preparation of Amines

5. Reactions of Amines

6. Key Reactions and Conversions

7. Important Concepts

8. Common Mistakes and Tips

Exam Tips & Common Mistakes

Common Mistakes and Exam Tips for Amines

Common Pitfalls

Tips for Success

Practice & Assessment

Multiple Choice Questions

Q1.Which reaction would you use to distinguish between methylamine and dimethylamine?

Correct Answer: B

Q2.Aniline reacts with acetic anhydride to form an acetanilide. What is the role of acetic anhydride in this reaction?

Correct Answer: C

Q3.Which of the following amines is more soluble in water?

Correct Answer: B

Q4.Which of the following amines is a primary amine?

Correct Answer: A

Q5.Which of the following compounds is a primary amine?

Correct Answer: A

Q6.Why are primary amines more soluble in water than tertiary amines?

Correct Answer: A

Q7.Which reaction is used to convert nitromethane into dimethylamine?

Correct Answer: A

Q8.Which compound is formed when C₆H₅NH₂ reacts with Br₂ (aq)?

Correct Answer: A

Q9.Which of the following reactions would most effectively distinguish between primary and secondary amines?

Correct Answer: A

Q10.Which of the following statements is true regarding the basicity of amines?

Correct Answer: B

Q11.Which reaction is used to convert nitrobenzene to aniline?

Correct Answer: C

Q12.Which of the following amines will most likely undergo the Hofmann elimination reaction to form an alkene?

Correct Answer: D

Q13.Which of the following is the correct increasing order of boiling points for the given compounds: C₂H₅OH, (CH₃)₂NH, C₂H₅NH₂?

Correct Answer: A

Q14.Consider the following reaction: An aromatic amine is treated with excess methyl iodide, followed by silver oxide and water. Which of the following is the major product?

Correct Answer: B

Q15.In the reaction of C₆H₅NH₂ with CHCl₃ and alcoholic KOH, which of the following is the major product?

Correct Answer: A

Q16.Which of the following amines has the highest boiling point?

Correct Answer: A

Q17.Why are primary amines more soluble in water compared to tertiary amines?

Correct Answer: A

Q18.In the reaction of C�6H�5N�2Cl with CuCN, followed by hydrolysis, which of the following compounds is formed?

Correct Answer: C

Q19.What is the expected product when aniline (C₆H₅NH₂) reacts with bromine water?

Correct Answer: A

Q20.Which of the following reactions can be used to convert benzamide to aniline?

Correct Answer: A

Q21.Which of the following compounds is expected to have the highest boiling point?

Correct Answer: D

Q22.Which of the following amines is expected to have the highest boiling point?

Correct Answer: A

Q23.Which of the following amines will have the highest solubility in water?

Correct Answer: C

Q24.Which reaction is used to convert benzamide to aniline?

Correct Answer: A

Q25.Which of the following statements explains why aliphatic amines are stronger bases than aromatic amines?

Correct Answer: A

Q26.What is the IUPAC name for the compound with the formula (CH₃)₂CHNH₂?

Correct Answer: B

Q27.Why are aromatic amines generally weaker bases than aliphatic amines?

Correct Answer: A

Q28.Which of the following compounds will form a compound 'C' with molecular formula C₆H₇N when treated with Br₂ and KOH?

Correct Answer: A

Q29.Which of the following reactions is used to convert aniline to 2,4,6-tribromoaniline?

Correct Answer: A

Q30.Why are aromatic primary amines less basic than aliphatic primary amines?

Correct Answer: A