Organic Chemistry: Nitrogen Compounds — IAL Edexcel Modular (Chemistry) Revision Notes & Topical Questions

Section 1 of 34Classifying and naming nitrogen compounds

Classifying and naming nitrogen compounds

Amines

• Amines derivatives of ammonia classified by the number of carbon groups on nitrogen.
• Primary is RNH₂, secondary is R₂NH and tertiary is R₃N.
• Aliphatic amines have alkyl groups and aromatic amines have an aryl group.
• Named with -amine, as in ethylamine, or amino-, as in aminoethane.

Amides

• Amides contain -CONR₂ and are named with -amide, as in ethanamide CH₃CONH₂.
• N-substituents are listed first with the prefix N-, as in N-propylethanamide.

Amino acids

• Amino acids carry -NH₂ and -COOH on the same carbon, RCH(NH₂)COOH, with 20 natural 2-amino acids.

Section 2 of 34Properties and basicity of amines

Solubility and smell

• Solubility and smell short-chain amines are water soluble through hydrogen bonding and smell fishy.
• Solubility falls as the carbon chain lengthens.

Alkaline solution

• CH₃CH₂NH₂ + H₂O ⇌ CH₃CH₂NH₃⁺ + OH^-.

Basicity

• Basicity depends on the availability of the nitrogen lone pair to accept H⁺ by a dative bond.
• Alkyl groups release electrons, so secondary > primary > ammonia.
• In phenylamine the lone pair is delocalised into the ring, so it is a weaker base than ammonia.

Section 3 of 34Reactions of amines

With acids

• With acids form ammonium salts.
• CH₃NH₂ + HCl → CH₃NH₃⁺Cl^-.
• Adding NaOH regenerates the amine.

With acyl chlorides

• With acyl chlorides give N-substituted amides plus HCl.

With halogenoalkanes

• With halogenoalkanes repeated substitution gives secondary amine, tertiary amine and finally a quaternary ammonium salt.

With copper(II) ions

• With copper(II) ions amines are lone pair donors like ammonia, giving a pale blue precipitate and then a deep blue solution in excess.

Section 4 of 34Preparing primary amines

From halogenoalkanes

• From halogenoalkanes heat with excess concentrated ethanolic ammonia in a sealed tube under pressure.
• Excess ammonia limits further substitution to secondary and tertiary amines.

From nitriles

• From nitriles reduce with LiAlH₄ in dry ether, or with H₂ over a nickel catalyst.

Section 5 of 34Phenylamine and azo dyes

Preparation

• Preparation reduce nitrobenzene with tin and concentrated HCl under reflux, then add excess NaOH to free the amine from C₆H₅NH₃⁺.
• Purify by steam distillation, salting out with NaCl, ether extraction and distillation (180-185 °C fraction).

Diazotisation

• Diazotisation phenylamine with nitrous acid (NaNO₂ + HCl) below 10 °C gives the benzenediazonium ion.
• Above 10 °C it decomposes to benzene and nitrogen.

Coupling

• Coupling the diazonium ion is an electrophile that substitutes into phenol at the 4-position in alkaline solution.
• The azo compound has a -N=N- link, extended delocalisation and bright colour, so it is used as a dye.

Section 6 of 34Amides

Formation

• Formation an acyl chloride condenses with ammonia (primary amide) or with an amine, losing HCl.
  • (N-substituted amide)
• CH₃CH₂COCl + 2NH₃ → CH₃CH₂CONH₂ + NH₄Cl.

Basicity

• Basicity amides are almost neutral because the nitrogen lone pair is delocalised towards the electronegative C=O group.

Section 7 of 34Condensation and addition polymers

Addition polymers

• Addition polymers monomers with C=C open and join;
  • the repeat unit has two backbone carbons and there is no by-product.

Condensation polymers

• Condensation polymers monomers with two functional groups join by ester or amide links, releasing H₂O or HCl.
• Unlike addition polymers, they can be hydrolysed at the links.
• Hydroxycarboxylic acids and amino acids can polymerise alone.

Polyester

• Polyester diol + dicarboxylic acid, as in PET from ethane-1,2-diol and benzene-1,4-dicarboxylic acid.

Section 8 of 34Polyamides and poly(ethenol)

1Nylon-6,6

• Nylon-6,6 from 1,6-diaminohexane and hexane-1,6-dioic acid.
  • (or the diacyl chloride)

2Kevlar

• Kevlar an aromatic polyamide from benzene-1,4-diamine and benzene-1,4-dicarboxylic acid.
• Rigid chains hydrogen bond strongly, giving great strength and fire resistance, used in bullet-proof vests.

3Properties

• Properties polyamides are tough, semi-crystalline and absorb moisture; hot acid or alkali hydrolyses them.

4Poly(ethenol)

• Poly(ethenol) an addition polymer made indirectly: polymerise ethenyl ethanoate, then ester exchange with methanol.
• Many -OH groups hydrogen bond to water, so it dissolves.
• Used for soluble hospital laundry bags and liquid-detergent capsules.

Section 9 of 34Amino acids

Zwitterion

• Zwitterion in the solid and in neutral solution amino acids exist as H₃N⁺-CHR-COO^-.
• Strong ionic attractions give high melting points, solubility in water and insolubility in non-polar solvents.

Amphoteric

• Amphoteric in acid the -COO^- is protonated to give a cation; in alkali -NH₃⁺ loses H⁺ to give an anion.

Isoelectric point

• Isoelectric point the pH at which the amino acid has no net charge.

Other reactions

• Other reactions the -NH₂ forms salts with acids and the -COOH forms salts with alkalis and esters with alcohols.

Optical activity

• Optical activity all except glycine are chiral and rotate plane-polarised light.

Section 10 of 34Peptides and proteins

Peptide link

• Peptide link an amide bond formed when -NH₂ of one amino acid condenses with -COOH of another, losing water.

Chains

• Chains dipeptide, tripeptide and then polypeptide or protein.

Hydrolysis

• Hydrolysis heating with 6 mol dm^-3 HCl breaks the peptide links and returns the amino acids.

Section 11 of 34Classifying amines

Classifying amines

Amines

• Amines derivatives of ammonia in which one or more hydrogens are replaced by an alkyl or aryl group.

Classification

• Classification by the number of carbon groups on the nitrogen.
• Primary has one, secondary has two and tertiary has three.
• This differs from alcohols and halogenoalkanes, where the classification depends on the carbon atom.

Aliphatic and aromatic

• Aliphatic and aromatic an alkyl group gives an aliphatic amine and an aryl (phenyl) group gives an aromatic amine.
• The aryl group strongly influences the reactivity of the amine group.

Section 12 of 34Naming amines, amides and amino acids

Amines

• Amines common name is the alkyl or aryl prefix plus -amine, as in ethylamine.
• The IUPAC name uses the amino- prefix with the stem, as in aminoethane or 1-aminopropane.

Amides

• Amides contain RCONR₂ and are formed from carboxylic acids or acyl chlorides with ammonia or amines.
• Primary amides add -amide to the stem, so CH₃CONH₂ is ethanamide.
• Secondary amides put the N-substituent first with the prefix N-, so CH₃CONH(C₃H₇) is N-propylethanamide.
• Tertiary amides list both N-groups alphabetically, so CH₃CON(CH₃)(C₃H₇) is N-methyl-N-propylethanamide.

Amide classes

• Amide classes primary, secondary and tertiary by the number of carbons on the amide nitrogen, one of which is the carbonyl carbon in secondary and tertiary amides.

Amino acids

• Amino acids contain a basic -NH₂ group and an acidic -COOH group, so they are amphoteric.
• The 20 natural 2-amino acids have the formula RCH(NH₂)COOH and are the building blocks of proteins.
• Three-letter codes are used, for example Gln for glutamine.

Section 13 of 34Solubility and basicity of amines

Solubility and basicity of amines

Solubility

• Solubility short-chain primary amines are miscible with water because they hydrogen bond to it.
• Solubility falls as the hydrocarbon chain lengthens.
• Phenylamine is only slightly soluble.

Weak alkalis

• CH₃NH₂ + H₂O ⇌ CH₃NH₃⁺ + OH^-.

Basicity

• Basicity the nitrogen lone pair accepts H⁺ by a dative bond, so Brønsted-Lowry basic strength depends on how available the lone pair is.

Positive inductive effect

• Positive inductive effect alkyl groups push electron density onto nitrogen, making it more basic.
• Secondary amines are stronger bases than primary amines, which are stronger than ammonia.

Delocalisation

• Delocalisation in phenylamine the lone pair delocalises into the benzene ring and is less available.
• Phenylamine is a weaker base than ethylamine and does not form a basic solution.

Section 14 of 34Reactions of amines

With acids

• With acids amines form ionic ammonium salts.
• CH₃NH₂ + HCl → CH₃NH₃⁺Cl^-.
• The salts are crystalline solids that dissolve in water, so phenylamine dissolves in acid.
• Adding NaOH to the salt regenerates the amine.

With ethanoyl chloride

• With ethanoyl chloride an addition-elimination reaction giving an N-substituted amide and HCl.
• CH₃COCl + CH₃CH₂CH₂CH₂NH₂ → CH₃CONHCH₂CH₂CH₂CH₃ + HCl.
• The mechanism is not required.

With copper(II) ions

• With copper(II) ions amines act as lone pair donors like ammonia.
• A pale blue precipitate of [Cu(H₂O)₄(OH)₂] forms first.
• Excess butylamine dissolves it to give a deep blue solution.

Section 15 of 34Amines and halogenoalkanes

Substitution

• Substitution the nitrogen lone pair attacks the electron-deficient carbon and replaces the halogen.
• R'NH₂ + R''X → R'NHR'' + HX.
• Butylamine with chloroethane gives a secondary amine and HCl.

Further substitution

• Further substitution each product still has a lone pair, so it can react again.
• A secondary amine gives a tertiary amine.
• A tertiary amine gives a quaternary ammonium salt, such as CH₃CH₂CH₂CH₂N⁺(CH₂CH₃)₃Cl^-.
• No HCl forms in the last step because the tertiary amine has no N-H to lose.

Quaternary ammonium salt

• Quaternary ammonium salt an ionic compound in which all hydrogens of the ammonium ion are replaced by alkyl groups.

Section 16 of 34Preparing primary aliphatic amines

From halogenoalkanes

• From halogenoalkanes nucleophilic substitution by ammonia.
• Heat the halogenoalkane with excess ethanolic ammonia under pressure.
• Excess ammonia favours the primary amine and limits further substitution.

Reduction of nitriles

• Reduction of nitriles the -CN group is reduced to -CH₂NH₂.
• Pass nitrile vapour and hydrogen over a nickel catalyst.
• Or use LiAlH₄ in dry ether.

Section 17 of 34Making and purifying phenylamine

1Phenylamine

• C₆H₅NH₂, also called aminobenzene or aniline.

2Stage 1

Stage 1 reduction

• nitrobenzene is heated under reflux in a boiling water bath with tin and concentrated HCl.
• C₆H₅NO₂ + 6[H] → C₆H₅NH₂ + 2H₂O, but in acid the product is the phenylammonium ion C₆H₅NH₃⁺.
• Tin is oxidised to Sn²⁺ and Sn⁴⁺.

3Stage 2

Stage 2 release

• excess NaOH deprotonates C₆H₅NH₃⁺ to phenylamine.
• Tin(II) and tin(IV) hydroxides also form.

4Stage 3

Stage 3 purification

• steam distillation gives a cloudy distillate.
• Add NaCl, which makes the aqueous layer more polar so phenylamine salts out.
• Extract with ether in a separating funnel, with the organic layer on top.
• Discard the aqueous layer, distil off the ether and keep the fraction boiling at 180-185 °C.
• Test the boiling point to check purity.

Section 18 of 34Diazonium salts and azo dyes

1

Make nitrous acid in situ from sodium nitrite (NaNO₂) and hydrochloric acid because it is unstable.

2

Diazotisation: react phenylamine with nitrous acid in dilute acid to give the benzenediazonium ion C₆H₅N₂⁺.

3

Keep the mixture below 10 °C with ice, otherwise the diazonium ion decomposes to benzene (or phenol) and nitrogen.

4

Coupling: the diazonium ion acts as an electrophile and substitutes into the ring of phenol at the 4-position.

5

Use alkaline conditions to deprotonate the phenol to the more reactive phenoxide and form the azo compound.

• Azo compound
  • contains R-N=N-R' linking two aromatic rings.
  • Delocalised electrons of both rings extend through the -N=N- bridge.
  • The molecule absorbs visible light, so it is brightly coloured and very stable, which makes azo compounds useful dyes.

Section 19 of 34Preparing amides

Preparing amides

Amides

• Amides contain -CONR₂ and are made by condensation of an acyl chloride with ammonia or an amine.
• Two molecules join and HCl is eliminated.

Mechanism idea

• Mechanism idea the electronegative chlorine makes the carbonyl carbon electron-deficient.
• The nitrogen lone pair acts as a nucleophile and attacks it, and the C-Cl bond breaks.

Product type

• Product type ammonia gives an unsubstituted amide while primary and secondary amines give substituted amides.

Equation

• Equation ammonia is basic and HCl is acidic, so they react: CH₃CH₂COCl + 2NH₃ → CH₃CH₂CONH₂ + NH₄Cl.

Section 20 of 34Addition and condensation polymerisation

1Addition polymerisation

• Addition polymerisation monomers containing C=C open and join, giving polymers such as poly(ethene), poly(chloroethene) and poly(ethenol).
• The repeat unit has the same atoms as the monomer with C=C changed to C-C.

2Condensation polymerisation

• Condensation polymerisation repeated condensation reactions between monomers, each eliminating a small molecule (water or HCl).
• Natural condensation polymers form by loss of water.
• Condensation polymers are recognised by ester or amide links between monomers.
• They form from dicarboxylic acids with diols, dicarboxylic acids with diamines, or from amino acids.

Feature	Addition	Condensation
Monomer	alkene with C=C	two functional groups, such as diol + diacid
By-product	none	H2O or HCl
Backbone	all carbon	contains ester or amide links
Biodegradable	generally not	can be hydrolysed

Section 21 of 34Repeat units and monomers

Repeat unit

• Repeat unit the smallest group of atoms that repeats along the chain, shown in square brackets with open bonds at both ends.

Addition polymers

• Addition polymers the repeat unit has only two carbon atoms in the main chain.
• Ethenol CH(OH)=CH₂ gives -CH(OH)-CH₂- (poly(ethenol)).
• Ethene-1,2-diol gives poly(ethene-1,2-diol) and propenoic acid gives poly(propenoic acid).

Finding the monomer

• Finding the monomer deduce the two-carbon repeat unit and put the C=C double bond back.

Condensation polymers

• Condensation polymers the repeat unit includes both monomer parts, joined by the ester or amide link.

Section 22 of 34Polyesters

Monomers

• Monomers a diol (two -OH groups) and a dicarboxylic acid.
  • (two -COOH groups)

Link

• Link an ester bond forms and water is expelled, from one H of the diol and one -OH of the -COOH.

PET

• PET poly, also called Terylene or Dacron, is made from ethane-1,2-diol and benzene-1,4-dicarboxylic acid.
  • (ethylene terephthalate)

Hydroxycarboxylic acids

• Hydroxycarboxylic acids one monomer with -OH at one end and -COOH at the other can polymerise alone.

Section 23 of 34Polyamides

Amide (peptide) link

• -CONH-, joins the repeat units of a polyamide.

Monomers

• Monomers a diamine (two -NH₂) and a dicarboxylic acid (two -COOH).
• A dioyl dichloride (two -COCl) can replace the acid, and it is more reactive but more expensive.
• A small molecule (water or HCl) is expelled at each link.

Nylon-6,6

• Nylon-6,6 made from 1,6-diaminohexane and hexane-1,6-dioic acid.
• The 6,6 refers to the six carbon atoms in each monomer.

Kevlar

• Kevlar made from benzene-1,4-diamine and benzene-1,4-dicarboxylic acid.
  • (or benzene-1,4-dioyl chloride)
• Chains are neatly arranged with many hydrogen bonds between them.
• It is strong, flexible and fire resistant, used in bullet-proof vests.

Section 24 of 34Properties and uses of polyamides

Properties and uses of polyamides

Structure

• Structure most nylons are semi-crystalline, tough and resistant to heat and chemicals.

Moisture

• Moisture polyamides absorb water until equilibrium.
• Impact resistance and flexibility increase.
• Strength and stiffness decrease.

Fibres

• Fibres strong amide bonds make strong fibres for clothing.

Film

• Film polyamide film is tough, stops gas molecules passing and resists high temperature.
• It is used for food packaging and boil-in-the-bag foods.

Section 25 of 34Poly(ethenol)

1Preparation

• Preparation it is not made from ethenol directly but in two stages.
• Polymerise ethenyl ethanoate to poly(ethenyl ethanoate).
• React it with methanol to give poly(ethenol) and methyl ethanoate (ester exchange).

2Control

• Control the extent of ester exchange is controlled by temperature.

3Solubility

• Solubility many -OH groups hydrogen bond to water.
• Solubility ranges from insoluble to soluble in warm water to soluble in cold water, depending on how many ester groups were replaced.

4Uses

• Uses water-soluble hospital laundry bags and liquid-detergent capsules.
• Soiled bedding is put into a bag that dissolves in the washing machine, so staff do not handle contaminated fabrics.
• Capsules release a measured quantity of detergent as they dissolve.

Section 26 of 34Amino acids to proteins

Proteins

• Proteins polymers of amino acid monomers, each with an amino group, an acid group and a unique R group.

Peptide formation

• Peptide formation the -NH₂ of one amino acid reacts with the -COOH of another, expelling water and forming an amide bond.
• Two amino acids give a dipeptide and more than two give a polypeptide.
• The repeat unit of the chain is -NH-CHR-CO-.

Names

• Names each amino acid has a three-letter code, such as Gln for glutamine.

Section 27 of 34Zwitterions and amino acid properties

Reactions

• Reactions amino acids undergo most reactions of both amines and carboxylic acids.

Zwitterion

• Zwitterion an ion with a positive -NH₃⁺ and a negative -COO^- group, formed when the molecule interacts with itself.
• In solution amino acids exist mainly as H₃N⁺-CHR-COO^-.

Physical properties

• Physical properties strong ionic attractions between zwitterions make amino acids soluble crystalline solids.

Section 28 of 34Buffer action and the isoelectric point

Buffer action and the isoelectric point

Buffer action

• Buffer action a solution of an amino acid resists small changes in pH.
• On adding acid, -COO^- accepts H⁺ to give -COOH and the ion carries a net +1 charge.
• On adding alkali, -NH₃⁺ loses H⁺ to give -NH₂ and the ion carries a net -1 charge.

Isoelectric point

• Isoelectric point the pH at which the amino acid exists as the neutral zwitterion, with neither positive nor negative ions dominating.
• It has no net movement in an electric field and minimum solubility.

Electrophoresis

• Electrophoresis below the isoelectric point the cation moves to the negative electrode.
• Above it the anion moves to the positive electrode.
• At the isoelectric point there is no net movement.

Effect of the R group

• Effect of the R group an extra acidic group (aspartic acid) gives a low isoelectric point and an extra basic group (lysine) gives a high one.

Section 29 of 34Reactions of the amine group

Reactions of the amine group

With acids

• With acids the basic -NH₂ group forms an ammonium salt.
• H₂NCHRCOOH + HCl → H₃N⁺CHRCOOH Cl^-.

With acyl chlorides

• With acyl chlorides gives an N-substituted amide.

Section 30 of 34Reactions of the carboxylic acid group

Reactions of the carboxylic acid group

With aqueous alkali

• With aqueous alkali forms a salt and water.
• H₂NCHRCOOH + NaOH → H₂NCHRCOO^-Na⁺ + H₂O.
• Glycine with NaOH gives H₂NCH₂COO^-Na⁺.

Esterification

• Esterification heat with an alcohol and concentrated sulfuric acid catalyst.
• H₂NCHRCOOH + C₂H₅OH + H⁺ → H₃N⁺CHRCOOC₂H₅ + H₂O.
• The carboxylic acid group is esterified while the amine group is protonated by the acid.

Section 31 of 34Optical activity of amino acids

Chiral centre

• Chiral centre almost all 2-amino acids have a chiral CH carbon, so they are optically active.

Glycine

• Glycine the exception, because its CH₂ group is not chiral.

Enantiomers

• Enantiomers aqueous solutions rotate the plane of plane-polarised light in opposite directions.
• Dextrorotatory (+) and laevorotatory (-).

Laboratory synthesis

• Laboratory synthesis gives a racemic mixture.

Section 32 of 34Peptide bonds

Peptide bond

• Peptide bond an amide bond between two amino acids.

Formation

• Formation the -NH₂ of one amino acid condenses with the -COOH of another, eliminating water to form a dipeptide.

Chain growth

• Chain growth the dipeptide still has a free -NH₂ and a free -COOH at its ends.
• It can react again to form a tripeptide.
• Many amino acids joined this way form a polypeptide.

Section 33 of 34Key terms

Term	Meaning
Diazotisation	Reaction of a primary aromatic amine with nitrous acid below 10 °C to form a diazonium ion.
Coupling reaction	Substitution of a diazonium ion into an activated ring to form an azo compound.
Condensation polymer	A polymer made by repeated condensation reactions that eliminate a small molecule.
Zwitterion	An ion with a positive and a negative charge and zero net charge.
Isoelectric point	The pH at which an amino acid has no net charge.
Peptide bond	The amide bond joining two amino acids.
Polyamide	A polymer with amide links such as nylon, Kevlar and proteins.

Term	Meaning
Primary amine	An amine with one carbon group bonded to the nitrogen atom.
Diazotisation	Reaction of a primary aromatic amine with nitrous acid below 10 °C to form a diazonium ion.
Coupling reaction	Substitution of a diazonium ion into an activated ring such as phenoxide to form an azo compound.
Azo compound	A compound with an -N=N- group linking two aromatic rings, often used as a dye.
Condensation reaction	A reaction in which two molecules join with loss of a small molecule such as HCl or water.
Quaternary ammonium salt	An ionic compound containing N bonded to four alkyl groups.
Amide	A compound containing the -CONR2 group.

Term	Meaning
Monomer	A small molecule that joins with others to form a polymer.
Repeat unit	The smallest unit that repeats along a polymer chain.
Polyamide	A polymer with amide links, such as nylon, Kevlar and proteins.
Polyester	A polymer with ester links, such as PET.
Dioyl dichloride	A compound with two -COCl groups, used in place of a dicarboxylic acid.
Condensation polymer	A polymer made by repeated condensation reactions that eliminate a small molecule.

Term	Meaning
Zwitterion	An ion carrying both a positive and a negative charge, with zero net charge.
Isoelectric point	The pH at which an amino acid has no net charge.
Peptide bond	The amide bond that joins two amino acids.
Amphoteric	Able to act as both an acid and a base.
Buffer	A solution that resists small changes in pH.
Racemic mixture	An equal mixture of two enantiomers that does not rotate polarised light.

Section 34 of 34Exam technique

1

Expecting a pure primary amine without excess ammonia — substitution continues.

2

Keeping diazotisation above 10 °C — the diazonium ion decomposes.

3

Saying amides are basic like amines — the lone pair is delocalised.

4

Drawing the amino acid in solution as neutral NH₂-CHR-COOH — it is a zwitterion.

5

Forgetting that water or HCl is released at every condensation link.

1

Expecting a pure primary amine from a halogenoalkane without excess ammonia — the product keeps reacting to give secondary, tertiary and quaternary products.

2

Keeping diazotisation at room temperature — above 10 °C the diazonium ion decomposes to nitrogen.

3

Coupling with phenol without alkaline conditions — the phenol must be deprotonated to react.

4

Saying amides are basic like amines — the nitrogen lone pair is delocalised onto the carbonyl.

5

Classifying amines by the carbon attached to the functional group — the class depends on the groups on nitrogen.

1

Forgetting that a polyamide made from a dioyl dichloride loses HCl, not water.

2

Giving an addition polymer repeat unit with four carbons in the backbone — it has two.

3

Saying polyesters are made from alkenes — they are made from diols and dicarboxylic acids.

4

Omitting the open bonds at the ends of the repeat unit.

1

Writing the neutral NH₂-CHR-COOH as the form in solution — amino acids exist mainly as zwitterions.

2

Confusing the isoelectric point with pH 7 — it depends on the R group.

3

Forgetting that water is released when a peptide bond forms.

4

Saying the zwitterion has no charges — it has both, with zero net charge.