Amines

NCERT Chemistry 12th Standard Flashcards

I. Fundamentals of Amines

What is the fundamental structural unit from which amines are derived?

Ammonia (NH₃)

How are amines structurally different from ammonia?

 One or more hydrogen atoms of ammonia are replaced by alkyl or aryl groups.

In what type of natural compounds can amines be found?

Proteins, vitamins, alkaloids, and hormones.

Give examples of synthetic products where amines are present.

Polymers, dye stuffs, and drugs.

Name two biologically active compounds containing secondary amino groups.

Adrenaline and ephedrine.

What is the use of Novocain in dentistry?

It is used as an anaesthetic.

What is the function of Benadryl?

It is an antihistaminic drug.

What type of compound are used as surfactants?

Quaternary ammonium salts

What is the role of diazonium salts in the synthesis of various compounds?

 They are used as intermediates in the preparation of a variety of aromatic compounds, including dyes.

What structural feature of amines is responsible for their basic properties?

The unshared pair of electrons on the nitrogen atom.

What type of hybridization does the nitrogen atom in amines possess?

sp³ hybridization.

Describe the geometry of amines.

Pyramidal.

Why is the bond angle in amines slightly less than 109.5°?

Due to the presence of the unshared pair of electrons, which exerts repulsion on the bonded pairs.

What is the bond angle in trimethylamine?

Approximately 108°.

How are amines classified based on the number of alkyl or aryl groups attached to the nitrogen atom?

Primary (1°), Secondary (2°), and Tertiary (3°).

Define a primary amine with a general formula.

R-NH₂ or Ar-NH₂

What is a secondary amine and what is its general formula?

An amine with two alkyl or aryl groups attached to the nitrogen atom; R-NH-R' or Ar-NH-R.

What is a tertiary amine, provide a general formula?

An amine with three alkyl or aryl groups attached to the nitrogen atom; R-N-R'-R" or R-N-R'-Ar

What is meant by a "simple" amine?

An amine where all the alkyl or aryl groups attached to nitrogen are the same.

How does a "mixed" amine differ from a "simple" amine?

A "mixed" amine has different alkyl or aryl groups attached to the nitrogen atom.

What is the common name of CH₃NH₂?

Methylamine.

How do you name an aliphatic amine in the common system?

By prefixing the name of the alkyl group to the word "amine."

How are secondary and tertiary amines with two or more identical groups named in the common system?

With the prefixes "di-" or "tri-" before the name of the alkyl group.

How are primary amines named in the IUPAC system?

As alkanamines.

What is the IUPAC name of CH₃CH₂NH₂?

Ethanamine.

How are amines with multiple amino groups named in the IUPAC system?

By using prefixes like di-, tri- and indicating the position of -NH₂ on the parent chain.

What is the IUPAC name of H₂N-CH₂-CH₂-NH₂?

Ethane-1,2-diamine.

How do you indicate substituents on the nitrogen atom in secondary and tertiary amines in the IUPAC system?

By using the locant "N".

What is the IUPAC name of CH₃NHCH₂CH₃?

N-methylethanamine

What is the common name of C₆H₅NH₂?

Aniline

How are arylamines named in the IUPAC system?

Replace the 'e' of arene by "amine"

What is the IUPAC name of C₆H₅NH₂?

Benzenamine

What is the common name of 2-methylaniline?

o-toluidine

What is the IUPAC name of p-bromoaniline?

4-bromobenzenamine or 4-bromoaniline

II. Preparation of Amines

What is the reducing agent used in the reduction of nitro compounds to amines, using metals in acidic media?

Sn+HCl or Fe+HCl

In the reduction of nitro compounds, why is iron scrap preferred over other metals?

FeCl₂ formed is hydrolyzed to release HCl, so only small amount is needed to initiate.

What is the process by which alkyl halides react with ammonia to form amines called?

Ammonolysis.

What kind of substitution reaction takes place during ammonolysis of alkyl halides?

Nucleophilic substitution reaction.

What byproducts are formed during ammonolysis of alkyl halides?

Mixtures of primary, secondary, tertiary amines, and quaternary ammonium salts.

How can a primary amine be obtained as the major product in the ammonolysis of alkyl halides?

By taking a large excess of ammonia.

Which alkyl halide reacts faster in ammonolysis: RI, RBr, or RCl?

RI (R-I)

What reducing agent can be used for the reduction of nitriles to amines?

LiAlH₄.

How is a primary amine prepared by using nitriles?

By reducing a nitrile using LiAlH₄ or catalytic hydrogenation.

In the reduction of nitriles, what happens to the carbon chain?

The carbon chain is increased by one.

What reducing agent is used for the reduction of amides to amines?

LiAlH₄

What product is formed from the reduction of amides using LiAlH₄?

An amine.

What is Gabriel Phthalimide synthesis used for?

Preparing primary amines.

Why can’t aromatic primary amines be prepared using the Gabriel phthalimide synthesis?

Because aryl halides do not undergo nucleophilic substitution with the anion formed by phthalimide

What is the key step in the Gabriel Phthalimide synthesis for preparing primary amines?

The reaction with the alkyl halide and alkaline hydrolysis.

What reaction is used for the synthesis of a primary amine containing one carbon less than the starting amide?

Hofmann Bromamide Degradation Reaction.

What are the reagents used in the Hofmann Bromamide degradation reaction?

Br₂ with aqueous or ethanolic NaOH.

What is the byproduct in Hoffmann Bromamide Degradation Reaction?

Carbonate, Sodium bromide, water

III. Physical Properties of Amines

What is the characteristic odor of lower aliphatic amines?

Fishy odor

How does the physical state of amines change with increasing molar mass?

Gases to liquids to solids

What is the typical appearance of aniline and other arylamines?

Colorless when pure but become colored on storage

Why are lower aliphatic amines soluble in water?

They can form hydrogen bonds with water molecules

How does the solubility of amines change with an increase in molar mass?

Solubility decreases due to increase in the size of the hydrophobic alkyl chain.

Which is more soluble in water, butan-1-ol or butan-1-amine, and why?

Butan-1-ol because it is more polar and forms stronger intermolecular hydrogen bonds than amines.

In what type of solvents are amines typically soluble?

Organic solvents like alcohol, ether, and benzene.

How does intermolecular association due to hydrogen bonding vary among primary, secondary, and tertiary amines?

Primary amines have more hydrogen bonding than secondary, while tertiary amines have no intermolecular hydrogen bonding between the molecules

Which type of isomeric amine has the highest boiling point: primary, secondary, or tertiary?

Primary amines.

What is the reason for the boiling point difference between isomeric amines?

The extent of intermolecular hydrogen bonding.

IV. Chemical Reactions of Amines

 Why are amines considered as Lewis bases?

They possess an unshared electron pair on the nitrogen atom.

 What products are formed when amines react with acids?

 Amine salts

How are parent amines regenerated from their salts?

By treatment with a base like NaOH.

Why are amine salts soluble in water but insoluble in organic solvents?

They are ionic compounds.

What are pKь and Kь values for amines useful for?

To understand the basic character of amines.

How does the +I effect of alkyl groups influence the basicity of amines?

Alkyl groups increase electron density on the nitrogen atom, making amines more basic than ammonia.

Are aliphatic amines or aromatic amines stronger bases than ammonia?

Aliphatic amines are stronger bases, while aromatic amines are weaker.

Why is aniline a weaker base than aliphatic amines?

The unshared pair of electrons on the nitrogen is delocalized into the benzene ring.

How do electron releasing groups influence the basic character of aromatic amines?

They increase the basic character of the amine.

How do electron withdrawing groups influence the basic character of aromatic amines?

They decrease the basic character of the amine.

What is the effect of steric hindrance on the basicity of amines?

Steric hindrance decreases basicity.

How does solvation influence the basicity of amines?

Smaller the ion, more is the solvation and more is its stabilization.

What is the general reaction for the alkylation of amines?

R-NH₂ + R'-X → R-NH-R' + HX (followed by subsequent alkylation)

What type of reaction is acylation of amines?

Nucleophilic substitution reaction.

What are the products of acylation of amines?

Amides

What reagents are used for acylation of amines?

Acid chlorides, anhydrides, esters

What type of base is required for acylation reactions of amines and why?

A stronger base than the amine (e.g., pyridine) to remove the HCl formed and shift the equilibrium.

What is the carbylamine reaction also known as?

Isocyanide test.

What type of amines respond to the carbylamine reaction?

Primary amines (both aliphatic and aromatic)

What are the products of carbylamine reaction?

Isocyanides or carbylamines which are foul smelling substances.

What are the products formed when primary aliphatic amines react with nitrous acid?

Unstable diazonium salt, which further decomposes to give alcohol and nitrogen gas.

What type of amines form stable diazonium salts when they react with nitrous acid?

Primary aromatic amines.

What is the use of quantitative evolution of nitrogen when amines react with nitrous acid?

For the estimation of amino acids and proteins.

How does the reaction with nitrous acid differ between primary, secondary, and tertiary amines?

Primary amines form diazonium salts, which may decompose, while secondary and tertiary amines form other different products.

What reagent is used for testing primary, secondary, and tertiary amines?

Benzenesulphonyl chloride (Hinsberg's reagent)

What is Hinsberg’s reagent and its structure?

Benzenesulphonyl chloride (C₆H₅SO₂Cl)

What type of compound is formed when a primary amine reacts with Hinsberg's reagent?

N-alkylbenzenesulphonamide

What property of N-alkylbenzenesulphonamides makes them soluble in alkali?

The hydrogen attached to nitrogen is strongly acidic.

What type of compound is formed when a secondary amine reacts with Hinsberg's reagent?

N,N-dialkylbenzenesulphonamide

Why do tertiary amines not react with benzenesulphonyl chloride?

Because they do not have hydrogen attached to the nitrogen atom.

What is the nature of the amino group in aromatic electrophilic substitution reactions?

Ortho- and para-directing, powerful activating group

What product is formed when aniline reacts with bromine water at room temperature?

2,4,6-tribromoaniline

What is the main issue encountered during electrophilic substitution reactions of aromatic amines?

Their very high reactivity.

How is the activating effect of the –NH₂ group in aniline controlled during monosubstitution reactions?

By protecting it by acetylation with acetic anhydride.