Nitrogen compounds

IntroNitrogen compounds and classes of amines

This unit studies organic compounds that contain nitrogen: amines, nitriles, amides, diazonium salts and azo compounds, and amino acids. Amines are the building blocks of amino acids, which in turn build proteins. Nitriles are used to make amines and acids with longer carbon chains, and diazonium salts are used to make dyes and drugs.

Amines are derivatives of ammonia, $\mathrm{NH}{}_3$, in which one or more hydrogen atoms are replaced by alkyl or aryl groups. They are classified by the number of carbon atoms joined to the nitrogen atom.

Phenylamine (aniline), $\mathrm{C}{}_6\mathrm{H}{}_5\mathrm{NH}{}_2$, is an aromatic amine: the $-\mathrm{NH}{}_2$ group is joined directly to a benzene ring. Its chemistry differs from that of alkylamines because the nitrogen lone pair interacts with the ring.

12.1Preparation of aminesOften examined

1. From halogenoalkanes and ammonia

A halogenoalkane is heated with an excess of concentrated ammonia in ethanol in a sealed tube (under pressure) at about $100^{\circ }\mathrm{C}$. The tube is sealed because ammonia is a gas and would escape on heating. Ethanol is the solvent; water is avoided because hydroxide ions would turn the halogenoalkane into an alcohol.

The reaction is a nucleophilic substitution. The lone pair on the nitrogen of ammonia attacks the $\delta +$ carbon of the halogenoalkane and the halide ion leaves. The ammonium salt formed then gives up a proton to a second ammonia molecule, freeing the amine.

ethylammonium bromide

ethylamine is released

overall

The reaction does not stop at the primary amine. Ethylamine also has a lone pair (it is an even better nucleophile than ammonia), so it attacks more bromoethane in the same two steps and gives a secondary amine. That reacts again to give a tertiary amine, and finally a quaternary ammonium salt:

diethylamine (secondary)

triethylamine (tertiary)

tetraethylammonium iodide (quaternary salt)

At the end, a strong alkali such as $\mathrm{KOH}$ is added to set the free amines loose from their salts (the quaternary salt is not affected, because its nitrogen has no H to lose). The three amines are then separated by fractional distillation. Using a large excess of ammonia makes the primary amine the main product, but some secondary and tertiary amines still form, so the yield of the primary amine is low. An excess of halogenoalkane favours the quaternary salt.

2. Secondary amines from halogenoalkanes and primary amines

To make a secondary amine on purpose, the halogenoalkane is heated with a primary amine (instead of ammonia) in ethanol, in a sealed tube or under pressure. The salt formed is then treated with a base.

3. Reduction of nitriles

Alkyl or aryl nitriles are reduced to primary amines. The reducing agent is lithium aluminium hydride ($\mathrm{LiAlH}{}_4$) in dry ether (followed by water), or sodium in ethanol. $[\mathrm{H}]$ stands for hydrogen supplied by the reducing agent.

ethanenitrile gives ethylamine

Catalytic reduction: nitriles also react with hydrogen gas over a heated nickel catalyst.

propanenitrile gives propylamine

4. Reduction of amides

With $\mathrm{LiAlH}{}_4$ the $\mathrm{C}=\mathrm{O}$ group of an amide is reduced to $\mathrm{CH}{}_2$, giving an amine with the same number of carbon atoms.

12.2Basicity of aminesOften examined

In amines the nitrogen atom is sp^3 hybridised. Three sp^3 orbitals form \sigma bonds to H or C atoms, and the fourth holds a lone pair. The shape is nearly tetrahedral; counting only the atoms it is trigonal pyramidal (bond angles about 107^\circ), just like ammonia.

The lone pair makes amines bases: it accepts a proton (\ce{H+}), exactly as in ammonia. When an amine dissolves in water, the lone pair takes a proton from a water molecule, forming an alkylammonium ion and hydroxide ions. The \ce{OH-} ions make the solution alkaline (it turns red litmus blue). Alkylamines are stronger bases than ammonia.

ethylamine gives the ethylammonium ion

K_b: base dissociation constant (\mathrm{mol\,dm^{-3}}). A larger K_b, or a **lower \mathrm{p}K_b, means a stronger base**.

Amines also neutralise acids, forming salts. These salts are ionic, crystalline and soluble in water. A strong alkali releases the free amine again.

ethylammonium chloride

12.2.1Relative basicities of ammonia, ethylamine and phenylamineOften examined

The strengths of weak bases are compared with their \mathrm{p}K_b values. The lower the \mathrm{p}K_b, the stronger the base.

Two factors decide the strength of a base

1. Availability of the lone pair: how easily the nitrogen lone pair can capture an \ce{H+} ion. More electron density on nitrogen means a stronger base.
2. Stability of the ion formed: how stable the positive ion is after it has received the \ce{H+} ion. A more stable cation means a stronger base.

Ethylamine is a stronger base than ammonia

The ethyl group is electron-donating (positive inductive effect, +I). It pushes electron density onto the nitrogen, so the lone pair is more electron-rich and attracts \ce{H+} more strongly. In the ethylammonium ion the ethyl group also partly cancels the positive charge on nitrogen, spreading it out, so this ion is more stable than the simple ammonium ion. Both factors make ethylamine the stronger base.

Phenylamine is a much weaker base than ammonia

In phenylamine the lone pair on nitrogen overlaps with the \pi electrons of the benzene ring and is delocalised over the ring. It is therefore much less available to bond with a proton, and the electron density around the nitrogen atom is much lower than in ammonia. In addition, when phenylamine does accept a proton, this delocalisation is lost, so the phenylammonium ion gets no extra stability.

Basicity in the gas phase and in water (beyond the book)

In the gas phase there are no solvent molecules, so only the inductive effect matters. Each extra alkyl group pushes more electron density onto nitrogen, and the order simply follows the number of alkyl groups:

In water a third factor appears: the cation formed is stabilised by hydrogen bonding with water molecules (solvation). \ce{RNH3+} has three \ce{N-H} bonds that can hydrogen-bond to water, \ce{R2NH2+} has two, and \ce{R3NH+} only one. Three bulky alkyl groups also crowd the nitrogen and hinder solvation. So the tertiary amine's cation is poorly stabilised in water, and the order changes:

12.3Formation of nitriles and hydroxynitrilesOften examined

1. From halogenoalkanes and KCN

Nitriles (alkyl cyanides) contain the \ce{-C#N} group. They are made by heating a halogenoalkane under reflux with potassium cyanide dissolved in ethanol. The cyanide ion is a nucleophile: it attacks the \delta+ carbon and the halide ion leaves (nucleophilic substitution). Ethanol is used as the solvent because in water the hydroxide ions would give an alcohol instead.

ethanenitrile (book: cyanomethane)

propanenitrile (book: cyanoethane)

A nitrile is named from the total number of carbon atoms including the carbon of \ce{-C#N}. So \ce{CH3CN} is ethanenitrile and \ce{CH3CH2CN} is propanenitrile.

2. Hydroxynitriles from aldehydes and ketones

Aldehydes and ketones add hydrogen cyanide across the \ce{C=O} double bond, forming hydroxynitriles (also called cyanohydrins). HCN is a very poisonous gas, so it is not used directly: the aldehyde or ketone is mixed with a solution of \ce{KCN} (or \ce{NaCN}) in water containing a little acid. The acid produces HCN in the mixture, but some free \ce{CN-} ions remain, and these catalyse the reaction.

formaldehyde cyanohydrin (2-hydroxyethanenitrile)

acetaldehyde cyanohydrin (2-hydroxypropanenitrile)

acetone cyanohydrin (2-hydroxy-2-methylpropanenitrile)

This is a nucleophilic addition. The cyanide ion attacks the \delta+ carbonyl carbon, the \ce{C=O} \pi electrons move onto oxygen, and the alkoxide ion formed takes a proton from HCN, regenerating \ce{CN-}:

Again the carbon chain grows by one carbon, so this reaction is also used in organic synthesis to increase chain length.

12.4Hydrolysis of nitrilesOften examined

Nitriles are hydrolysed by heating under reflux with dilute acid or dilute alkali. The \ce{-C#N} group becomes \ce{-COOH} (or its salt) and the nitrogen leaves as ammonia or an ammonium salt. The reaction passes through an amide:

Acid hydrolysis

When a nitrile is heated under reflux with dilute hydrochloric acid or dilute sulphuric acid, a carboxylic acid is formed directly. The ammonia produced reacts with the acid to give an ammonium salt.

ethanenitrile gives ethanoic acid

Alkaline hydrolysis followed by acidification

When a nitrile is heated under reflux with dilute sodium hydroxide solution, the sodium salt of the carboxylic acid is formed and ammonia gas is given off (it turns damp red litmus blue). Acidifying with dilute hydrochloric acid then gives the free carboxylic acid.

12.5 (a)Reaction of phenylamine with bromine waterOften examined

When bromine water is added to an aqueous solution of phenylamine at room temperature, the reddish-brown colour of bromine is decolourised at once and a white precipitate of 2,4,6-tribromophenylamine forms. No catalyst is needed.

The \ce{-NH2} group makes the ring very reactive. The nitrogen lone pair is delocalised into the ring and raises the electron density, especially at positions 2, 4 and 6 (see the resonance structures in 12.2.1). The ring is so electron-rich that it polarises bromine molecules itself and is attacked by them (electrophilic substitution) at all three positions.

Benzene, by contrast, reacts with bromine only in the presence of a halogen carrier such as \ce{FeBr3}, and gives just one substitution product (bromobenzene). Phenol behaves like phenylamine and gives 2,4,6-tribromophenol with bromine water.

12.5 (b)Diazotisation: preparing benzenediazonium chlorideOften examined

Phenylamine reacts with nitrous acid, \ce{HNO2}, and dilute hydrochloric acid at a low temperature to give benzenediazonium chloride (also called phenyl diazonium chloride). This reaction is called diazotisation.

Nitrous acid is unstable, so it is made in the mixture from sodium nitrite and hydrochloric acid:

overall

Procedure

1. Phenylamine is dissolved in excess dilute hydrochloric acid and the solution is cooled in ice to below 5^\circ\mathrm{C}.
2. A solution of sodium (or potassium) nitrite is also cooled in ice.
3. The ice-cold nitrite solution is added slowly, with stirring, to the phenylamine solution. The temperature must never go above 5^\circ\mathrm{C}.
4. The solution of benzenediazonium chloride formed is used at once; it is not stored or dried.

Why the mixture is kept so cold

• Diazonium salts are unstable. Above about 10^\circ\mathrm{C} the diazonium ion reacts rapidly with water, losing nitrogen gas and forming phenol. The desired product would be lost.
• Nitrous acid decomposes on warming, so it would be lost before it could react.
• The reaction gives out heat, so the nitrite is added slowly to stop the temperature rising.
• Dry diazonium salts can explode, which is why they are kept in cold solution and used immediately.

Benzenediazonium ions are stable enough to use at 0 to 5^\circ\mathrm{C} because the positive charge is partly delocalised into the benzene ring. Diazonium ions made from alkylamines (such as ethylamine) have no ring to stabilise them and decompose immediately, even in the cold, giving off nitrogen.

12.6Reactions of benzenediazonium chloride and azo dyesOften examined

1. Reaction with water: phenol

When an aqueous solution of benzenediazonium chloride is warmed (to about 50^\circ\mathrm{C}), it decomposes: bubbles of nitrogen gas are given off and phenol is formed. This is the way to convert phenylamine into phenol.

2. Coupling with phenol: azo compounds

Phenol is dissolved in sodium hydroxide solution to form sodium phenoxide, and the solution is cooled in ice. When it is mixed with ice-cold benzenediazonium chloride solution, a coupling reaction takes place between the phenoxide ion and the diazonium ion. A yellow-orange solution or precipitate of 4-hydroxyazobenzene forms.

sodium phenoxide

4-hydroxyazobenzene, 4-(phenylazo)phenol

The diazonium ion is a weak electrophile. It can only attack a strongly activated ring, such as phenoxide, and it substitutes at the 4-position (para to \ce{-O-}). The alkali converts phenol into phenoxide, whose ring is even more electron-rich. The cold keeps the diazonium ion from decomposing.

The azo group and azo dyes

The product contains the azo group, \ce{-N=N-}, which links two benzene rings through a nitrogen bridge. Compounds containing this group are called azo compounds. The azo group joins the two rings into one long delocalised system that absorbs visible light, so azo compounds are strongly coloured and are used as azo dyes. Azo dyes are the largest class of dyes: the book puts them at more than 60% of all dyes (about 70% of industrial dyes).

Other azo dyes by the same route

Changing the coupling partner changes the colour. When ice-cold benzenediazonium chloride is shaken with phenylamine, a yellow solid dye, aniline yellow (4-aminoazobenzene), is formed.

Coupling with naphthalen-2-ol (2-naphthol) in alkali gives an orange-red dye; methyl orange, the acid-base indicator, is also an azo dye.

Diazonium salts in synthesis (beyond the book)

The \ce{-N2+} group leaves very easily as nitrogen gas, one of the most stable molecules. So it can be replaced by many groups that cannot be put onto a benzene ring directly. This makes diazonium salts very useful in organic synthesis.

12.7Preparation of amides

Amides contain the group \ce{-CONH2} (or \ce{-CONHR}, \ce{-CONR2}). They are made from acyl chlorides by the nucleophilic addition-elimination mechanism of Unit 11.

1. Acyl chloride with ammonia

Acyl chlorides react with ammonia at room temperature to give amides. The hydrogen chloride produced reacts with excess ammonia to give ammonium chloride.

ethanamide

2. Acyl chloride with a primary amine

Primary amines react in the same way at room temperature to give N-substituted amides. The HCl reacts with excess amine to give an alkylammonium salt.

methanamine (methylamine) gives N-methylethanamide

12.7.1Reactions of amidesOften examined

1. Reduction to amines

When an amide is treated with lithium aluminium hydride, \ce{LiAlH4}, the \ce{C=O} group is reduced to \ce{CH2} and a primary amine is formed. The carbon chain stays the same length.

the book prints 2[H]; 4[H] is needed to balance

2. Hydrolysis

Amides are hydrolysed by heating under reflux with dilute acid or dilute alkali. The \ce{C-N} bond breaks.

(a) Acid hydrolysis

Heating with dilute hydrochloric acid or dilute sulphuric acid gives the carboxylic acid and an ammonium salt.

ethanamide gives ethanoic acid

(b) Alkaline hydrolysis

Heating with dilute sodium hydroxide solution gives the sodium salt of the carboxylic acid and ammonia gas. The salt gives the free acid on acidification with dilute hydrochloric acid.

12.7.2Why amides are much weaker bases than aminesOften examined

Amides contain an \ce{-NH2} group, but they are much weaker bases than amines. Aqueous solutions of amides are practically neutral to litmus, and amides do not form stable salts with dilute acids.

1. Delocalisation (resonance). The lone pair on the nitrogen of an amide is delocalised onto the carbonyl group. Part of the electron density moves onto the electronegative oxygen, and the \ce{C-N} bond gets partial double-bond character. The lone pair is no longer free to accept a proton.

2. Inductive effect. The carbonyl group is strongly electron-withdrawing. It pulls electrons away from the nitrogen, lowering the electron density there still further.

In amines neither effect exists: the lone pair on nitrogen is not delocalised, and alkyl groups push electron density onto the nitrogen (+I effect). So amines attract protons strongly. If an amide is protonated at all (only by very strong acids), the proton goes onto the oxygen, not onto the nitrogen.

12.8Amino acids

Compounds that contain an amino group (\ce{-NH2}) and a carboxylic acid group (\ce{-COOH}) are called amino acids. So an amino acid has two functional groups: a basic one (\ce{-NH2}) and an acidic one (\ce{-COOH}).

Amino acids are the building blocks of proteins. Twenty different amino acids are used in protein synthesis. According to the book, the body can make ten of them; these are non-essential amino acids. The other ten are essential amino acids: the body cannot make them, so they must be present in the diet.

General formula: the central carbon carries an amino group, a carboxylic acid group, a hydrogen atom and a side chain R, which is different in each amino acid.

In the amino acids of proteins the amino group is on the carbon atom **next to the \ce{-COOH} group. They are called 2-amino acids or \alpha-amino acids**.

Except in glycine, the central carbon carries four different groups, so these amino acids are chiral and optically active.

12.8.1Zwitterions and the acid-base properties of amino acidsOften examined

An amino acid has both a basic amine group and an acidic carboxylic acid group in the same molecule. A hydrogen ion moves internally from the \ce{-COOH} group to the \ce{-NH2} group. This leaves an ion with a positive charge and a negative charge, called a zwitterion (from the German for 'double ion').

glycine: neutral form and zwitterion

A zwitterion has no overall electrical charge, but it contains separate parts that are positively and negatively charged.

Physical properties

Amino acids exist as zwitterions even in the solid state. The forces between neighbouring zwitterions are strong ionic attractions, like those in a salt. These need a lot of energy to break, so amino acids are crystalline solids with high melting points (glycine decomposes at about 233^\circ\mathrm{C}). For the same reason they dissolve in water but not in non-polar solvents.

Acid-base (amphoteric) properties

The zwitterion contains an acidic site (\ce{-NH3+}, which can donate \ce{H+}) and a basic site (\ce{-COO-}, which can accept \ce{H+}). So amino acids react with both acids and bases; they are amphoteric.

in acid (low pH): the basic site accepts a proton, giving a positive ion

in alkali (high pH): the acidic site loses a proton, giving a negative ion

The pH at which an amino acid is present as the zwitterion, with no net charge, is its isoelectric point (pI). For glycine it is about 6.0. Because amino acids can remove both \ce{H+} and \ce{OH-}, their solutions resist changes in pH (they act as buffers).

12.8.2Formation of the peptide bondOften examined

Amino acid molecules join through the amino group (\ce{-NH2}) of one molecule and the carboxyl group (\ce{-COOH}) of another. A molecule of water is eliminated (a condensation reaction), and the two units are joined by an amide linkage \ce{-CO-NH-}, called a peptide bond. The product of two amino acids is a dipeptide.

For example, glycine and alanine can join in two different ways, giving two different dipeptides:

Gly-Ala

A dipeptide still has a free amino group at one end and a free carboxyl group at the other. Each can react with more amino acids. A dipeptide joined to one more amino acid is a tripeptide (two peptide bonds, two water molecules eliminated). In the same way thousands of amino acid units join into a giant protein molecule. A chain of n amino acids contains n-1 peptide bonds.

The reverse reaction, hydrolysis, breaks peptide bonds and gives back the amino acids. It happens when a protein is boiled with hydrochloric acid, and in digestion, where enzymes (proteases) catalyse it.

12.8.3Electrophoresis of amino acids and dipeptidesOften examined

Electrophoresis is a technique that separates charged molecules, such as amino acids and peptides, using an electric field. A strip of paper or gel is soaked in a buffer of known pH and placed between two electrodes. A spot of the mixture is placed at the centre and a voltage is applied. Each species moves according to its charge. Afterwards the strip is dried and sprayed with ninhydrin, which shows the amino acids as coloured spots.

The pH of the buffer controls the charge of each amino acid:

• At low pH (below its pI) an amino acid is protonated (\ce{-NH3+} and \ce{-COOH}), carries a positive charge and moves towards the cathode (negative electrode).
• At high pH (above its pI) it is deprotonated (\ce{-NH2} and \ce{-COO-}), carries a negative charge and moves towards the anode (positive electrode).
• At its isoelectric point it is a zwitterion with no net charge and does not move.

The speed of movement depends on the size of the charge (a larger charge moves faster) and on the size (mass) of the molecule (a smaller molecule moves faster). Different amino acids have different pI values and masses, so they end up in different places and are separated.

Dipeptides behave in the same way. Their charge depends on the free \ce{-NH3+} and \ce{-COO-} groups at the chain ends (and any charged side chains), so it also changes with pH. A dipeptide is heavier than the amino acids it is made from, so with the same charge it moves more slowly.

Formula sheet

Key terms

Amine

A derivative of ammonia in which one or more H atoms are replaced by alkyl or aryl groups.

Primary, secondary, tertiary amine

An amine with one (\ce{RNH2}), two (\ce{R2NH}) or three (\ce{R3N}) carbon atoms bonded to the nitrogen.

Quaternary ammonium salt

An ionic compound \ce{R4N+X-} in which nitrogen is bonded to four carbon atoms and has no lone pair.

Phenylamine (aniline)

\ce{C6H5NH2}, the simplest aromatic amine.

Nitrile

A compound containing the \ce{-C#N} group, for example ethanenitrile \ce{CH3CN}.

Hydroxynitrile (cyanohydrin)

A compound with \ce{-OH} and \ce{-CN} on the same carbon, formed by adding HCN to an aldehyde or ketone.

Base (Brønsted-Lowry)

A proton (\ce{H+}) acceptor; amines accept protons with the lone pair on nitrogen.

Kb and pKb

K_b is the base dissociation constant; \mathrm{p}K_b=-\log_{10}K_b. The lower the \mathrm{p}K_b, the stronger the base.

Positive inductive effect (+I)

Electron donation through \sigma bonds by groups such as alkyl groups; it increases the electron density on nitrogen.

Delocalisation

Spreading of a lone pair or charge over several atoms, for example the nitrogen lone pair of phenylamine into the benzene ring.

Solvation

Stabilisation of an ion by surrounding solvent molecules; alkylammonium ions are stabilised by hydrogen bonds to water.

Nitrogen inversion

Rapid turning inside out of an amine's pyramidal shape, which stops amines with three different groups from being optically active.

Amide

A compound containing \ce{-CONH2} (or \ce{-CONHR}, \ce{-CONR2}); a very weak base.

N-substituted amide

An amide in which an H atom on nitrogen is replaced by an alkyl group, for example N-methylethanamide \ce{CH3CONHCH3}.

Diazotisation

The reaction of a primary aromatic amine with nitrous acid and HCl at 0 to 5^\circ\mathrm{C} to form a diazonium salt.

Diazonium salt

A salt containing the \ce{Ar-N#N+} ion, such as benzenediazonium chloride; unstable above about 10^\circ\mathrm{C}.

Coupling reaction

The reaction of a diazonium ion with an activated aromatic compound (phenol or phenylamine) to form an azo compound.

Azo group

The group \ce{-N=N-} that links two aromatic rings in azo compounds.

Azo dye

A strongly coloured azo compound used as a dye, for example 4-hydroxyazobenzene and aniline yellow.

Amino acid

A compound containing both an amino group (\ce{-NH2}) and a carboxylic acid group (\ce{-COOH}).

Alpha-amino acid (2-amino acid)

An amino acid in which the amino group is on the carbon next to the \ce{-COOH} group.

Essential amino acid

An amino acid the body cannot make, so it must be obtained from the diet.

Zwitterion

An ion that carries both a positive and a negative charge but has no overall charge, for example \ce{H3N+CH2COO-}.

Amphoteric

Able to react both as an acid and as a base; amino acids are amphoteric.

Isoelectric point (pI)

The pH at which an amino acid exists as a zwitterion with no net charge and does not move in an electric field.

Peptide bond

The amide linkage \ce{-CO-NH-} that joins two amino acid units, formed with loss of water.

Dipeptide, tripeptide

Molecules formed from two or three amino acids joined by one or two peptide bonds.

Electrophoresis

A technique that separates charged molecules such as amino acids and peptides by their movement in an electric field.

FBISE 2026 questions

Questions from the FBISE HSSC-II 2026 (1st Annual) papers that belong to this unit, answered the way an examiner expects.

Exam focus

1. State two factors that affect the basic strength of amines and explain the order ethylamine > ammonia > phenylamine. (long)
   Asked in both new 2026 sets (Set B Q.4 OR, 7 marks; Set D Q.5 OR, 6 marks), both with the order printed in reverse.
   Go to answer
2. Why are amides much weaker bases than amines? (short)
   2026 Set D Q.2 (x) OR and a book short question; the resonance structure earns the marks.
   Go to answer
3. Write the equations for diazotisation of phenylamine and explain why it is done below 5^\circ\mathrm{C}. (short)
   2026 Set B Q.2 (viii) OR and MCQ 9; the book asks it as short iii and long iv.
   Go to answer
4. Draw the zwitterion of an amino acid and label its acidic and basic sites; explain amphoteric behaviour. (short)
   2026 Set B Q.2 (ix); also a book short and long question.
   Go to answer
5. Predict the results of electrophoresis of amino acids and dipeptides at pH 3, at the pI and at pH 11. (long)
   Three book questions; use the pH versus pI rule, then charge and size.
   Go to answer
6. Show the formation of a dipeptide and a tripeptide and the role of peptide bonds. (long)
   Two book long questions; name the condensation and show the water lost.
   Go to answer
7. Hydrolysis of nitriles with dilute acid, and with dilute alkali followed by acidification. (long)
   SLO reaction and a book long question; conditions and both sets of equations are needed.
   Go to answer
8. Coupling of benzenediazonium chloride with phenol in NaOH; the azo group and azo dyes. (short)
   SLO reaction; the structure of the azo group was a book exercise MCQ.
   Go to answer
9. Why is methylamine more basic than ammonia, and why is trimethylamine weaker than methylamine in water? (short)
   Old-syllabus 2026 Q.2 (vi) OR and Set D MCQ 12 test the inductive effect and solvation.
   Go to answer
10. Preparation of primary and secondary amines, and reduction of nitriles and amides with \ce{LiAlH4}. (short)
    Four book exercise MCQs and a short question test these reagents and conditions.
    Go to answer
11. Reaction of phenylamine with bromine water. (short)
    Two book exercise MCQs; the balanced equation needs 3 Br2.
    Go to answer