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Notes/Chemistry/Paper 1/Nitrogen Compounds
CAIEAS Level9701§19

Nitrogen Compounds

Amines and nitriles: making them from halogenoalkanes and carbonyl compounds, why cyanide adds one carbon to the chain, and how a nitrile is hydrolysed to a carboxylic acid.

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In the Carboxylic Acids and Derivatives note you made acids by hydrolysing nitriles. This note covers two families of nitrogen compounds: amines, which contain an −NH2-\text{NH}_2 group, and nitriles, which contain a −C≡N-\text{C}{\equiv}\text{N} group. Both are made by reactions you already know: ammonia or cyanide ions replacing the halogen of a halogenoalkane, and HCN adding across the C=O of an aldehyde or ketone.

You start by naming the families, then make amines, then nitriles and hydroxynitriles (nitriles that also carry an −OH-\text{OH}), then hydrolyse nitriles to carboxylic acids, with a short look at reducing nitriles to amines. By the end you can give the reagents and conditions for each step, write the equations, count carbons through a route and follow a reaction scheme that passes through nitrogen.

Before you start you should be able to

  • Ammonia's lone pair and its behaviour as a base (AS Nitrogen and Sulfur note)

  • Nucleophilic substitution of halogenoalkanes, and why aqueous and ethanolic conditions give different products (AS Halogen Compounds note)

  • Nucleophilic addition of HCN to aldehydes and ketones, with KCN as catalyst (AS Carbonyl Compounds note)

  • Carboxylic acids and esters, ester hydrolysis, and LiAlH₄ reducing acids to alcohols (AS Carboxylic Acids and Derivatives note)

  • Naming organic compounds and reading skeletal formulae (AS Introduction to Organic Chemistry note)

  • Moles, masses, percentage yield and gas volumes at room conditions (AS Atoms, Molecules and Stoichiometry note)

By the end of this page you can

  • Name nitriles, hydroxynitriles and amines, counting the C≡N carbon as C1 of a nitrile

  • Recall how amines are made: a halogenoalkane with NH₃ in ethanol heated under pressure, and write RX + 2NH₃ → RNH₂ + NH₄X

  • Recall how nitriles are made: a halogenoalkane with KCN in ethanol and heat, and explain why KCN in ethanol is used rather than HCN(aq)

  • Recall how hydroxynitriles are made: an aldehyde or ketone with HCN, KCN as catalyst, and heat

  • Use the +1 carbon rule for both cyanide routes to count carbons forwards and backwards through a scheme

  • Describe the hydrolysis of nitriles with dilute acid, or with dilute alkali followed by acidification, and write balanced equations for both

  • Write the equation for reducing a nitrile to a primary amine (RCN + 2H₂ → RCH₂NH₂) when a question describes it, and use it in a gas-volume calculation

  • Follow multi-step reaction schemes that pass through amines and nitriles

01

Meet the nitrogen families

One atom, two disguises

Nitrogen has five outer electrons. Three of them form bonds; the other two stay together as a lone pair.

At AS, nitrogen appears in organic molecules in two ways:

  • The amine: nitrogen joined to the carbon chain as −NH2-\text{NH}_2. Its lone pair is free, so an amine behaves like ammonia: it is a weak base and a nucleophile (you study amines as bases at A Level).
  • The nitrile: nitrogen at the end of a C≡N\text{C}{\equiv}\text{N} triple bond. Nitrogen is more electronegative than carbon, so the carbon is Cδ+\text{C}^{\delta+}, like a carbonyl carbon. You will convert this group into a carboxylic acid (see “Hydrolysing nitriles”).

The questions ask how you would make these compounds, and the answer is always one of the nucleophile reactions from earlier notes. First, though, you need to name them — and nitrile names hide a counting trap.

Naming rules

Nitriles: the CN carbon counts as carbon 1. The suffix -nitrile includes the nitrile carbon in the chain length:

  • CH3CN\text{CH}_3\text{CN} — ethanenitrile: TWO carbons in total (CH3\text{CH}_3 + the CN carbon), not one-plus-one;
  • CH3CH2CN\text{CH}_3\text{CH}_2\text{CN} — propanenitrile: three in total;
  • CH3CH2CH2CN\text{CH}_3\text{CH}_2\text{CH}_2\text{CN} — butanenitrile: four in total.

Branches number from the CN carbon: CH3CH(CN)CH3\text{CH}_3\text{CH(CN)CH}_3 is 2-methylpropanenitrile — a three-carbon chain (CN carbon + two others) carrying a methyl on C2, four carbons in all.

Hydroxynitriles — the products of adding HCN across a C=O — keep the same counting and show the −OH-\text{OH} as a prefix (hydroxy-): (CH3)2C(OH)CN(\text{CH}_3)_2\text{C(OH)CN} is 2-hydroxy-2-methylpropanenitrile, because both the OH and the extra methyl sit on C2, the carbon that was the carbonyl carbon. The chain is still numbered from the C≡N\text{C}{\equiv}\text{N} end.

Amines name the carbon chain and suffix -amine, with a locant giving which carbon carries the nitrogen: CH3CH2CH2NH2\text{CH}_3\text{CH}_2\text{CH}_2\text{NH}_2 is propan-1-amine (also called propylamine or 1-aminopropane), CH3CH(NH2)CH3\text{CH}_3\text{CH(NH}_2)\text{CH}_3 is propan-2-amine. A primary amine has its nitrogen bonded to one carbon only. The syllabus says "Classification of amines will not be tested at AS Level", so you will not be asked to sort amines into primary, secondary and tertiary.

Two families, one lone pairAMINERNHHlone pair — exposedthe lone pair is free to act: amines areweak bases and nucleophilesNITRILERCNδ+δ−lone pairpolar C≡N: nucleophiles attack the Cδ+;–CN → –COOH (hydrolysis)Names you must get right firstpropanenitrileCH₃CH₂CN: the CN carbon is C1,so 3 carbons in total, not 2 + 12-hydroxypropanenitrileCH₃CH(OH)CN, from ethanal + HCN;OH is a prefix, numbered from C≡N2-hydroxy-2-methylpropanenitrile(CH₃)₂C(OH)CN, from propanone + HCN;the OH and the CH₃ are both on C2propan-1-amineCH₃CH₂CH₂NH₂: suffix -amine, andthe locant is the carbon carrying N“Classification of amines will not betested at AS Level” — AS syllabus

The two families side by side: where nitrogen's lone pair sits in each, and the four naming patterns the papers test — nitrile chains counting the CN carbon, hydroxynitrile prefixes, amine locants, and the syllabus's own scoping line on classification.

Naming all three families

Name each compound, and state how many carbons it contains in total:

(i) CH3CH2CH2CN\text{CH}_3\text{CH}_2\text{CH}_2\text{CN}

(ii) CH3CH(CN)CH3\text{CH}_3\text{CH(CN)CH}_3

(iii) (CH3)2C(OH)CN(\text{CH}_3)_2\text{C(OH)CN}

(iv) CH3CH(NH2)CH2CH3\text{CH}_3\text{CH(NH}_2)\text{CH}_2\text{CH}_3

Show full working
  1. 1

    (i) Split the formula into groups: CH3\text{CH}_3, CH2\text{CH}_2, CH2\text{CH}_2 (three carbons) and CN (one more carbon). Total = 4 carbons, so the stem is butane: butanenitrile.

    Each CH₃, CH₂ or CH group is one carbon, and the CN adds one more. The usual slip is to forget the CN carbon and write 'propanenitrile'.

  2. 2

    (ii) Number from the CN carbon: C1 = CN carbon, C2 = the CH carrying a CH3\text{CH}_3 branch, C3 = the other CH3\text{CH}_3. The longest chain is 3 carbons with a methyl on C2: 2-methylpropanenitrile, 4 carbons in total.

    In a nitrile, numbering always starts at the CN carbon, so branch positions are counted from there.

  3. 3

    (iii) C1 = CN carbon. C2 carries an −OH-\text{OH} and a CH3\text{CH}_3; the other CH3\text{CH}_3 is C3. Prefixes go in alphabetical order (hydroxy before methyl): 2-hydroxy-2-methylpropanenitrile, 4 carbons in total.

    Both groups sit on C2, so both get the locant 2. The chain is still numbered from the CN end.

  4. 4

    (iv) The chain has four carbons and the N is on the second one: butan-2-amine, 4 carbons in total.

    Amines are numbered from whichever end gives the N the lower number. This is different from nitriles, where C1 is always the CN carbon.

Answer

(i) butanenitrile, 4 C (ii) 2-methylpropanenitrile, 4 C (iii) 2-hydroxy-2-methylpropanenitrile, 4 C (iv) butan-2-amine, 4 C

Your turn

Naming practice. Every later section assumes you can count carbons in these names quickly.

  1. 13 marks

    Name each compound.

    (a) CH3CH2CN\text{CH}_3\text{CH}_2\text{CN}

    (b) CH3CH2CH2CH2NH2\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{NH}_2

    (c) CH3CH(OH)CN\text{CH}_3\text{CH(OH)CN}

    Stuck? Show hint

    For (a) and (c), count the CN carbon in the chain. For (b), number from the end nearer the N.

    Show solution
    1. 1

      (a) CH3\text{CH}_3 + CH2\text{CH}_2 + the CN carbon = 3 carbons: propanenitrile.

      The CN carbon is part of the chain, so the stem is propane, not ethane.

    2. 2

      (b) Four carbons in a chain, N on the end carbon: butan-1-amine.

      For an amine, the stem counts only the carbon chain; the locant 1 says the N is on the end carbon.

    3. 3

      (c) C1 = CN carbon, C2 = the CH carrying −OH-\text{OH}, C3 = CH3\text{CH}_3. Three carbons with OH on C2: 2-hydroxypropanenitrile.

      Hydroxy is a prefix on the nitrile name, and its locant is counted from the CN carbon.

    Answer

    (a) propanenitrile (b) butan-1-amine (c) 2-hydroxypropanenitrile

  2. 23 marks

    Give the structural formula of each compound and state the total number of carbon atoms in it.

    (a) pentanenitrile

    (b) propan-2-amine

    (c) 2-hydroxy-2-methylbutanenitrile

    Stuck? Show hint

    Draw the stem chain first, then put the groups on the numbered carbons. In a nitrile, C1 is the CN carbon.

    Show solution
    1. 1

      (a) Pentane stem = 5 carbons, and C1 is the CN carbon. So four carbons come before it: CH3CH2CH2CH2CN\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{CN}, 5 C.

      A common slip is to write five carbons and THEN add CN, giving six. The CN carbon is one of the five.

    2. 2

      (b) Propane stem = 3 carbons, N on C2 (the middle carbon): CH3CH(NH2)CH3\text{CH}_3\text{CH(NH}_2)\text{CH}_3, 3 C.

      The locant tells you which carbon carries the N; the middle carbon of a three-carbon chain is C2 from either end.

    3. 3

      (c) Butane stem = 4 carbons with C1 = CN. C2 carries an −OH-\text{OH} and a CH3\text{CH}_3 branch; C3 and C4 complete the chain: CH3CH2C(CH3)(OH)CN\text{CH}_3\text{CH}_2\text{C(CH}_3)(\text{OH})\text{CN}, 5 C (4 in the chain + 1 in the branch).

      Count branches too when a question asks for the total number of carbons.

    Answer

    (a) CH₃CH₂CH₂CH₂CN, 5 C (b) CH₃CH(NH₂)CH₃, 3 C (c) CH₃CH₂C(CH₃)(OH)CN, 5 C

The rest of this note

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Can you do all of these?

  • Nitrile names COUNT the CN carbon — propanenitrile is 3 carbons in total

  • Amine conditions quoted in full: NH₃ in ETHANOL, heated UNDER PRESSURE (sealed tube); equation carries 2NH₃ → RNH₂ + NH₄X

  • KCN in ethanol with heat, never HCN(aq): free CN⁻ is the nucleophile, and HCN gives almost none

  • Hydroxynitriles: aldehyde or ketone + HCN, with KCN as catalyst, and heat

  • Cyanide routes GROW the chain by one carbon; hydrolysis and reduction PRESERVE it

  • Hydroxynitriles carry the OH prefix numbered from the C≡N end — 2-hydroxypropanenitrile, not '2-hydroxyethanenitrile'

  • Acid hydrolysis gives RCOOH + NH₄⁺; alkaline gives RCOO⁻Na⁺ + NH₃ until you acidify

  • If a question describes nitrile reduction: RCN + 2H₂ → RCH₂NH₂, N on the end carbon, count unchanged

Paper 1 · MCQ
Real past-paper questions, sorted by difficulty, with mark schemes
Paper 2 · Theory
Real past-paper questions, sorted by difficulty, with mark schemes
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