What are nitriles and how are they relevant in AS-Level Organic Chemistry?

Nitriles are organic compounds that contain a cyano group (-C≡N) attached to an alkyl group. In AS-Level Organic Chemistry, particularly under the Cambridge International A Levels curriculum, nitriles are studied for their unique properties and reactions, such as their ability to undergo hydrolysis to form carboxylic acids. Understanding nitriles is crucial for grasping the broader topic of nitrogen compounds.

How are hydroxynitriles formed in organic chemistry reactions?

Hydroxynitriles are formed through the nucleophilic addition of hydrogen cyanide (HCN) to aldehydes or ketones. This reaction is significant in AS-Level Organic Chemistry as it introduces students to the concept of nucleophilic addition, a fundamental reaction mechanism. The resulting hydroxynitrile contains both a hydroxyl group (-OH) and a cyano group (-C≡N), showcasing the versatility of organic synthesis.

What is the importance of studying nitriles and hydroxynitriles in the context of nitrogen compounds?

Studying nitriles and hydroxynitriles is important because they serve as intermediates in the synthesis of various nitrogen-containing compounds. In the Cambridge International A Levels Chemistry syllabus, these compounds help illustrate key concepts such as functional group transformations and reaction mechanisms, which are essential for understanding the behavior of nitrogen in organic molecules.

Can you explain the hydrolysis of nitriles and its significance in organic synthesis?

The hydrolysis of nitriles involves converting the cyano group into a carboxylic acid group through reaction with water, often in the presence of an acid or base catalyst. This reaction is significant in organic synthesis as it provides a pathway to synthesize carboxylic acids from nitriles. In AS-Level Organic Chemistry, understanding this transformation is crucial for mastering the synthesis and reactivity of nitrogen compounds.

What are some common applications of nitriles and hydroxynitriles in real-world chemistry?

Nitriles and hydroxynitriles have several applications in real-world chemistry. Nitriles are used in the production of pharmaceuticals, agrochemicals, and synthetic fibers like nylon. Hydroxynitriles, due to their functional groups, are valuable intermediates in the synthesis of amino acids and other biologically active compounds. These applications highlight the practical importance of studying these compounds in the Cambridge International A Levels Chemistry curriculum.

Why is "Confusing KCN/ethanol (substitution) with HCN/KCN (addition)." a common mistake in Nitriles and hydroxynitriles?

Why it happens: Both use cyanide. How to avoid it: Halogenoalkane + KCN/ethanol → nitrile; carbonyl + HCN/KCN → hydroxynitrile. Source: 9701 Examiner Reports 2022-2024

Why is "Not converting –CN to –COOH on hydrolysis." a common mistake in Nitriles and hydroxynitriles?

Why it happens: Forgetting the product. How to avoid it: Nitrile hydrolysis gives a carboxylic acid (+ NH₄⁺ salt).

Why is "Mixing up reduction and hydrolysis of a nitrile." a common mistake in Nitriles and hydroxynitriles?

Why it happens: Both start from –CN. How to avoid it: Reduction (LiAlH₄) → amine; hydrolysis (acid/water) → carboxylic acid.

Why is "Saying the hydroxynitrile is a single enantiomer." a common mistake in Nitriles and hydroxynitriles?

Why it happens: Ignoring the planar carbonyl. How to avoid it: The planar C=O is attacked equally from both sides → a racemic (50:50) mixture.

Nitrogen compounds(AS-Level Organic Chemistry)Cambridge International A Level Chemistry 9701

Nitriles and hydroxynitriles

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Nitriles and Hydroxynitriles — Cambridge International AS & A Level Chemistry 9701 (2025-2027 syllabus)

How nitriles and hydroxynitriles are made (both adding a carbon via CN⁻), and the hydrolysis of nitriles to carboxylic acids — key chain-lengthening steps in organic synthesis.

What you’ll learn

Mapped to the Cambridge International A Level 9701 syllabus (2025-2027).

19.2.1 — Recall how nitriles can be produced: the reaction of a halogenoalkane with KCN in ethanol and heat.
19.2.2 — Recall how hydroxynitriles can be produced: the reaction of aldehydes and ketones with HCN, KCN as catalyst, and heat.
19.2.3 — Describe the hydrolysis of nitriles with dilute acid or dilute alkali followed by acidification to produce a carboxylic acid.

Making nitriles and hydroxynitriles

CN⁻ adds a carbon — by substitution to a halogenoalkane, or by addition to a carbonyl.

Both reactions introduce a –C≡N (nitrile) group, which lengthens the carbon chain by one — a valuable synthetic step.

Nitriles — from halogenoalkanes (nucleophilic substitution): heat with KCN in ethanol: $\text{CH}_3\text{CH}_2\text{Br} + \text{KCN} \rightarrow \text{CH}_3\text{CH}_2\text{CN} + \text{KBr}$ (propanenitrile from bromoethane — one extra carbon.)

Hydroxynitriles — from aldehydes/ketones (nucleophilic addition): react with HCN with a KCN catalyst, heat: $\text{CH}_3\text{CHO} + \text{HCN} \rightarrow \text{CH}_3\text{CH(OH)CN}$ (2-hydroxypropanenitrile; see the mechanism in Topic 17.1.) The product has both an –OH and a –CN group.

Note the solvent. KCN in ethanol with a halogenoalkane gives substitution (nitrile); KCN/HCN with a carbonyl gives addition (hydroxynitrile).

Halogenoalkane + KCN/ethanol → nitrile (substitution).
Carbonyl + HCN (KCN catalyst) → hydroxynitrile (addition).
Both add one carbon to the chain.

Hydrolysis of nitriles to carboxylic acids

Reflux a nitrile with dilute acid (or alkali then acidify) to get a carboxylic acid.

Nitriles are hydrolysed to carboxylic acids by refluxing with dilute acid (or dilute alkali, then acidifying):

With dilute acid: $\text{CH}_3\text{CH}_2\text{CN} + 2\text{H}_2\text{O} + \text{HCl} \rightarrow \text{CH}_3\text{CH}_2\text{COOH} + \text{NH}_4\text{Cl}$

With dilute alkali (then acidify): gives the carboxylate salt first, which is acidified to the carboxylic acid.

The two-step chain extension (halogenoalkane → nitrile → carboxylic acid) is a standard synthesis route: e.g. bromoethane → propanenitrile → propanoic acid (adding one carbon overall).

Reflux nitrile with dilute acid → carboxylic acid + NH₄⁺ salt.
Or dilute alkali, then acidify.
Chain extension: halogenoalkane → nitrile → carboxylic acid.

How it’s examined

Nitrile formation and hydrolysis appear in synthesis-route questions where a carbon must be added. Examiner reports flag confusing the KCN/ethanol (substitution) and HCN/KCN (addition) conditions, and forgetting that hydrolysis converts –CN to –COOH.

Sources: Cambridge International AS & A Level Chemistry 9701 syllabus (2025-2027), section 19.2; 9701 Examiner Reports 2022-2024; 9701/22 May/Jun 2024 question paper and mark scheme. Last reviewed 2026-05-20.

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Step-by-step worked examples — Nitriles and hydroxynitriles

Step-by-step solutions to past-paper-style questions on nitriles and hydroxynitriles, written exactly the way a tutor would explain them at the board.

1Making a nitrile (2 marks)
Getting started• nitrile
Question
Give the reagents/conditions and equation to convert 1-bromopropane into butanenitrile.
Step-by-step solution
1. Step 1
  KCN in ethanol, heat (nucleophilic substitution).
  $\text{CH}_3\text{CH}_2\text{CH}_2\text{Br} + \text{KCN} \rightarrow \text{CH}_3\text{CH}_2\text{CH}_2\text{CN} + \text{KBr}$
Answer
KCN/ethanol, heat; adds one carbon to give butanenitrile.
Examiner tip
KCN extends the chain by one carbon (–CN) — note butanenitrile (C4) from a C3 halide.
2Making a hydroxynitrile (2 marks)
Getting started• hydroxynitrile
Question
Give the product and conditions for the reaction of ethanal with HCN.
Step-by-step solution
1. Step 1
  HCN with KCN catalyst (nucleophilic addition).
  $\text{CH}_3\text{CHO} + \text{HCN} \rightarrow \text{CH}_3\text{CH(OH)CN}$
Answer
2-hydroxypropanenitrile, CH₃CH(OH)CN (HCN, KCN catalyst).
3Hydrolysis of a nitrile (3 marks)
Building confidence• hydrolysis
Question
Write the equation for the hydrolysis of ethanenitrile (CH₃CN) with dilute hydrochloric acid.
Step-by-step solution
1. Step 1
  Reflux with dilute acid → carboxylic acid + ammonium salt.
  $\text{CH}_3\text{CN} + 2\text{H}_2\text{O} + \text{HCl} \rightarrow \text{CH}_3\text{COOH} + \text{NH}_4\text{Cl}$
Answer
CH₃CN + 2H₂O + HCl → CH₃COOH + NH₄Cl.
Examiner tip
The –CN becomes –COOH; nitrogen leaves as an ammonium salt.
4Reduction of a nitrile (3 marks)
Building confidence• reduction
Question
Give the reagents and product when ethanenitrile (CH₃CN) is reduced.
Step-by-step solution
1. Step 1
  Reduce with LiAlH₄ (or H₂ + Ni catalyst).
2. Step 2
  –CN becomes –CH₂NH₂ → a primary amine.
  $\text{CH}_3\text{CN} + 4[\text{H}] \rightarrow \text{CH}_3\text{CH}_2\text{NH}_2$
Answer
LiAlH₄ (or H₂/Ni); CH₃CN → CH₃CH₂NH₂ (ethylamine).
Examiner tip
Hydrolysis of a nitrile → carboxylic acid; reduction of a nitrile → amine. Don't mix them up.
5Chain extension in synthesis (4 marks)
Stretch• synthesis, chain extension
Question
Show how to convert bromoethane (C₂) into propanoic acid (C₃), explaining why a nitrile intermediate is useful.
Step-by-step solution
1. Step 1
  Step 1: KCN/ethanol, heat → propanenitrile (adds a carbon).
  $\text{CH}_3\text{CH}_2\text{Br} + \text{KCN} \rightarrow \text{CH}_3\text{CH}_2\text{CN} + \text{KBr}$
2. Step 2
  Step 2: reflux with dilute acid → propanoic acid.
  $\text{CH}_3\text{CH}_2\text{CN} + 2\text{H}_2\text{O} + \text{HCl} \rightarrow \text{CH}_3\text{CH}_2\text{COOH} + \text{NH}_4\text{Cl}$
3. Step 3
  Why useful: the C–C bond formed by KCN lengthens the carbon chain by one carbon — hard to do otherwise.
Answer
Bromoethane → propanenitrile (KCN) → propanoic acid (hydrolysis); the nitrile step adds a carbon.
Examiner tip
Nitrile formation is the key C–C bond-making step for extending a carbon chain.
6Hydroxynitriles and racemic mixtures (4 marks)
Stretch• hydroxynitrile, optical isomerism
Question
When ethanal reacts with HCN, the hydroxynitrile is a racemic mixture. Explain why, and state what it gives on hydrolysis. (4)
Step-by-step solution
1. Step 1
  Ethanal's carbonyl carbon is planar (sp²), so CN⁻ can attack from either face.
2. Step 2
  Attack is equally likely from both sides → equal amounts of the two enantiomers.
3. Step 3
  The product has a chiral centre (C bonded to H, OH, CH₃, CN) → a 50:50 racemic mixture (optically inactive).
4. Step 4
  On hydrolysis the –CN becomes –COOH → 2-hydroxypropanoic acid (lactic acid).
Answer
Planar carbonyl → equal attack on both faces → racemic mixture; hydrolyses to 2-hydroxypropanoic acid.
Examiner tip
The new chiral centre + equal attack on a planar C=O is the standard reason for a racemate.

Key Definitions and Keywords — Nitriles and hydroxynitriles

Definitions to memorise and the exact keywords mark schemes credit for nitriles and hydroxynitriles answers — sharpened from recent examiner reports for the 2026 Cambridge International A Level 9701 sitting.

Nitrile
Examiner keyword
A compound containing the –C≡N group, made from a halogenoalkane and KCN (chain extended by one carbon).
Hydroxynitrile
Examiner keyword
A compound with both –OH and –CN groups, made by nucleophilic addition of HCN to a carbonyl.
Nitrile hydrolysis
Examiner keyword
Reflux with dilute acid (or alkali then acidify) converts –CN to –COOH (a carboxylic acid).
Nitrile reduction
Examiner keyword
LiAlH₄ (or H₂ + Ni) converts –CN to –CH₂NH₂ (a primary amine), keeping the same carbon count.
Chain extension
Examiner keyword
Adding a carbon to a chain by making a nitrile with KCN — a key C–C bond-forming step in synthesis.

Common Mistakes and Misconceptions — Nitriles and hydroxynitriles

The traps other students keep falling into on nitriles and hydroxynitriles questions — taken from recent Cambridge International A Level 9701 examiner reports and mark schemes — and how to avoid them.

✕Confusing KCN/ethanol (substitution) with HCN/KCN (addition).
9701 Examiner Reports 2022-2024
Why it happens
Both use cyanide.
How to avoid it
Halogenoalkane + KCN/ethanol → nitrile; carbonyl + HCN/KCN → hydroxynitrile.
✕Not converting –CN to –COOH on hydrolysis.
Why it happens
Forgetting the product.
How to avoid it
Nitrile hydrolysis gives a carboxylic acid (+ NH₄⁺ salt).
✕Mixing up reduction and hydrolysis of a nitrile.
Why it happens
Both start from –CN.
How to avoid it
Reduction (LiAlH₄) → amine; hydrolysis (acid/water) → carboxylic acid.
✕Saying the hydroxynitrile is a single enantiomer.
Why it happens
Ignoring the planar carbonyl.
How to avoid it
The planar C=O is attacked equally from both sides → a racemic (50:50) mixture.

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Nitriles and hydroxynitriles — frequently asked questions

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Nitriles and hydroxynitriles

Short Study Notes in the form of Slides

Short Study Notes — Nitriles and hydroxynitriles

Detailed Notes

What you’ll learn

How it’s examined

1Making a nitrile (2 marks)

2Making a hydroxynitrile (2 marks)

3Hydrolysis of a nitrile (3 marks)

4Reduction of a nitrile (3 marks)

5Chain extension in synthesis (4 marks)

6Hydroxynitriles and racemic mixtures (4 marks)

Nitrile

Hydroxynitrile

Nitrile hydrolysis

Nitrile reduction

Chain extension

✕Confusing KCN/ethanol (substitution) with HCN/KCN (addition).

✕Not converting –CN to –COOH on hydrolysis.

✕Mixing up reduction and hydrolysis of a nitrile.

✕Saying the hydroxynitrile is a single enantiomer.

Practice questions

Past paper style quiz

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Nitriles and hydroxynitriles — frequently asked questions