6.4Organic Chemistry and Analysis

Nitrogen Compounds — OCR A Level Chemistry A H432 Revision Notes & Topical Questions

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📚 OCR A Level Chemistry A H432 Hub / Topical Revision

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Lesson summary

Complete PDF with figures and original page layoutPage 1 OCR A Level Chemistry A Your notes Nitrogen Compounds Contents Amines Preparing Amines Amino acids Amides Page 2 Amines …

Part 1 of 8Classifying and naming amines

Classifying and naming amines

Amines

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

They are classified by the number of hydrogens replaced on nitrogen: primary, secondary or tertiary.
This differs from alcohols and haloalkanes, where classification depends on the carbon atom.

Aliphatic or aromatic

Aliphatic or aromatic aliphatic if R is alkyl, aromatic if R is aryl (a benzene ring)
They share similar reactions but the aryl group strongly influences reactivity.

Naming

Common names use the alkyl or aryl prefix plus -amine.
IUPAC names use the prefix amino- with the alkane or aromatic stem.

Part 2 of 8Basicity of amines

Base behaviour

Base behaviour the nitrogen can accept a proton by donating its lone pair, forming a dative bond
Ammonia with HCl gives NH₄⁺Cl⁻.
Ethylamine with HCl gives the salt ethylammonium chloride, C₂H₅NH₃⁺Cl⁻.

Salts

Salts amine salts are ionic and soluble
They are water soluble when the alkyl group is small, and less so as the chain lengthens.

Bronsted–Lowry

Bronsted–Lowry ammonia and amines are proton acceptors

Part 3 of 8Preparing aliphatic primary amines

From halogenoalkanes

From halogenoalkanes nucleophilic substitution with ammonia
The nitrogen lone pair acts as a nucleophile and replaces the halogen.
Use excess hot ethanolic ammonia under pressure to give a primary amine.

By reduction of nitriles

By reduction of nitriles the –CN group is reduced to –NH₂
Pass nitrile vapour and hydrogen over a nickel catalyst, or use LiAlH₄ in dry ether.

Part 4 of 8Preparing secondary and tertiary amines

ammonia primary secondary tertiary amines

Secondary amine

Secondary amine a halogenoalkane with a primary amine in ethanol, heated in a sealed tube under pressure
It is nucleophilic substitution, with the amine nitrogen as the nucleophile.

Tertiary amine

Tertiary amine further substitution of the secondary amine
An example is the formation of triethylamine, (CH₃CH₂)₃N.

Part 5 of 8Preparing aromatic amines

1Phenylamine

Phenylamine a benzene ring bonded to an –NH₂ group, made by reducing nitrobenzene (C₆H₅NO₂) in two stages

2Stage 1

Stage 1 reduction
Nitrobenzene is heated under reflux in a boiling water bath with tin and concentrated hydrochloric acid, which act as the reducing agents.
The acidic conditions give phenylammonium ions, C₆H₅NH₃⁺.

3Stage 2

Stage 2 formation of phenylamine
Excess sodium hydroxide solution deprotonates the phenylammonium ions to give C₆H₅NH₂.

Part 6 of 8Amino acids

Amino acid

Amino acid a compound with a basic amino group (–NH₂) and an acidic carboxylic acid group (–COOH)

It is amphoteric, acting as both an acid and a base.

2-aminocarboxylic acids

2-aminocarboxylic acids the –NH₂ is on the carbon next to the –COOH
They are the building blocks of proteins.
There are 20 naturally occurring ones, with general formula RCH(NH₂)COOH.
The R group varies and may be acidic, basic or neutral.

Part 7 of 8Reactions of amino acids

Reactions of amino acids

Amine group

Amine group it is basic and reacts with acids to make ammonium salts, e.g. with HCl

Carboxylic acid group

Carboxylic acid group it reacts with aqueous alkalis such as NaOH to form a sodium salt and water

Esterification

Esterification heating with an alcohol and concentrated sulfuric acid esterifies the carboxylic acid group
The amine group is protonated under the acidic conditions.

Part 8 of 8Amides

Amides

Amides formed by condensation of carboxylic acids or acyl chlorides with ammonia or amines, with general structure RCONR₂
They occur in nature, e.g. in proteins where amino acids link through amide bonds.

Classification

Type	Description
Classification	by the number of carbons bonded to the amide nitrogen
Primary	one carbon (the carbonyl carbon), so two hydrogens remain on N.
Secondary	two carbons on N, one of which must be the carbonyl carbon.
Tertiary	three carbons on N, one of which must be the carbonyl carbon.

Naming

Primaryadd -amide to the stem, e.g. CH₃CONH₂ is ethanamide.
Secondarythe alkyl group on N is added first with the prefix N-, e.g. CH₃CONH(C₃H₇) is N-propylethanamide.
Tertiaryboth N-alkyl groups are listed alphabetically (with di- if needed), e.g. N-methyl-N-propylethanamide.

Key terms

Term	Meaning
Amine	A derivative of ammonia with one or more hydrogens replaced by alkyl or aryl groups
Amphoteric	Able to act as both an acid and a base
Amino acid	A compound containing both –NH₂ and –COOH groups
Amide	A compound containing the –CONR₂ group
Phenylamine	An aromatic amine, C₆H₅NH₂
Nucleophilic substitution	Replacement of a halogen by a nucleophile

Avoid these mistakes

Classifying amines by the carbon environment as for alcohols — it depends on groups on nitrogen

Saying amines act as acids — the nitrogen lone pair accepts H⁺

Giving only one reducing stage for nitrobenzene — the phenylammonium ion must be deprotonated with NaOH

Forgetting the N- prefix on alkyl groups on the amide nitrogen

Last updated: 29 October 2026