# Amides

> Chemistry · CIE A-Level 9701
> Source: https://www.owlsprep.com/study/cie-9701-u26-amides/

This module covers amide structure, IUPAC naming, physical properties, and core organic reactions, fully aligned to CIE A-Level 9701 A2 assessment requirements.

**Prerequisites:** [Carboxylic acids and acyl chlorides](https://www.owlsprep.com/study/cie-9701-u26-acyl-chlorides/); [Nucleophilic acyl substitution basics](https://www.owlsprep.com/study/cie-9701-u26-nucleophilic-acyl-substitution/)

## Learning objectives

- Recall the general structure and IUPAC naming rules for primary, secondary and tertiary amides
- Describe physical properties of amides including boiling point and solubility trends
- Explain nucleophilic acyl substitution hydrolysis of amides under acidic and alkaline conditions
- Predict products of amide dehydration and reduction reactions in synthetic pathways

## Structure and Naming of Amides

Amides are classified as primary, secondary or tertiary based on the number of alkyl groups bonded directly to the nitrogen atom. Primary amides have no alkyl substituents on N, secondary have one, and tertiary have two.

**IUPAC Naming Rule for Amides** — The parent name comes from the longest carbon chain containing the amide functional group, replacing the -oic acid suffix of the corresponding carboxylic acid with -amide. Alkyl groups attached to nitrogen are prefixed with N- to indicate their position.

- Primary amide from ethanoic acid = ethanamide
- Secondary amide with one methyl on N = N-methylethanamide
- Tertiary amide with two methyl groups on N = N,N-dimethylethanamide

**Worked example:** Name the amide with structure CH₃CH₂C(=O)NHCH₃

1. Step 1: Identify the longest carbon chain containing the amide group. This is 3 carbons, derived from propanoic acid.
2. Step 2: The suffix for a 3-carbon amide is -propanamide.
3. Step 3: There is one methyl group attached to the nitrogen atom, so add the N-methyl prefix.
4. Final name: N-methylpropanamide

**Check your understanding**

1. Which of the following is the correct name for CH₃C(=O)N(CH₃)₂?

   - N,N-dimethylethanamide
   - 2-dimethylethanamide
   - di-N-methylmethanamide

   *Why:* The parent chain is 2 carbons (ethanamide), with two methyl groups bonded to nitrogen.

## Physical Properties of Amides

Primary amides have two N-H bonds that can form strong hydrogen bonds between adjacent molecules, leading to much higher boiling points than comparable carboxylic acids, alcohols or amines. Low molecular weight amides are fully miscible with water due to hydrogen bonding with water molecules.

| Compound | Relative molecular mass | Boiling point / °C |
| --- | --- | --- |
| Propan-1-ol | 60 | 97 |
| Ethanoic acid | 60 | 118 |
| Ethanamide | 59 | 221 |

> **tip**
>
> You will often be asked to explain the unusually high boiling point of amides in 2-mark exam questions, always reference the extra hydrogen bonding from the N-H groups and the partial double bond character of the C-N bond.

**Worked example:** Explain why ethanamide has a higher boiling point than ethanoic acid of similar molecular mass

1. Step 1: Both molecules form hydrogen bonds between their functional groups.
2. Step 2: Ethanamide has two polar N-H bonds that can act as hydrogen bond donors, and the carbonyl oxygen acts as an acceptor, forming a more extensive intermolecular hydrogen bond network.
3. Step 3: The partial double bond character of the C-N bond in amides increases the polarity of the functional group, further strengthening intermolecular forces.
4. Conclusion: More energy is required to separate amide molecules, leading to a higher boiling point.

## Hydrolysis of Amides

**Exam command terms**

CIE uses specific command terms for amide hydrolysis questions, note their requirements:

- **Describe hydrolysis** — State reagents, conditions and products only

- **Outline mechanism** — Draw full nucleophilic acyl substitution electron movement arrows

Amide hydrolysis is the reverse of amide formation, and proceeds via nucleophilic acyl substitution. It requires heating under reflux with either strong aqueous acid or strong aqueous alkali.

> **warning**
>
> The products of hydrolysis differ significantly under acidic vs alkaline conditions, this is a very common exam trick question.

**Worked example:** State the products of full hydrolysis of propanamide under (i) acidic conditions with dilute HCl, heat and (ii) alkaline conditions with aqueous NaOH, heat

1. Part (i): Acidic hydrolysis
2. The amide bond breaks, the -OH from water adds to the acyl group to form propanoic acid, and the NH₂ group is protonated by excess HCl to form ammonium chloride.
3. $$CH_3CH_2CONH_2 + H_2O + HCl \rightarrow CH_3CH_2COOH + NH_4Cl$$
4. Part (ii): Alkaline hydrolysis
5. The amide bond breaks, the Na⁺ from the alkali forms a propanoate salt, and ammonia gas is released. Free propanoic acid is only formed if you add a subsequent acidification step.
6. $$CH_3CH_2CONH_2 + NaOH \rightarrow CH_3CH_2COO^-Na^+ + NH_3$$

## Reduction and Dehydration of Amides

**Comparing methods**

Two key synthetic reactions of primary amides are tested regularly in CIE A-Level exams:

- **Reduction with LiAlH₄** — Lithium aluminium hydride in dry ether reduces the carbonyl C=O group to a CH₂ group, leaving the C-N bond intact.
  - Pros: Produces an amine with exactly the same number of carbon atoms as the starting amide
  - Cons: Requires strictly anhydrous conditions

- **Dehydration with P₄O₁₀** — Strong heating with the dehydrating agent phosphorus(V) oxide removes one molecule of water from the primary amide to form a nitrile.
  - Pros: High yield, one step conversion of amide to nitrile
  - Cons: Requires very high temperatures

**Worked example:** Predict the organic products of (i) reduction of benzamide with LiAlH₄ in dry ether, and (ii) dehydration of benzamide with P₄O₁₀

1. Step 1: For LiAlH₄ reduction, convert the C=O group of benzamide (C₆H₅CONH₂) to CH₂, giving C₆H₅CH₂NH₂ (phenylmethanamine). No carbon atoms are lost.
2. Step 2: For dehydration, remove one H₂O molecule from benzamide, giving C₆H₅CN (benzonitrile). The nitrile functional group has the same number of carbon atoms as the starting amide.

## Common pitfalls

- **Wrong:** Stating alkaline amide hydrolysis directly produces a free carboxylic acid
  - Why it fails: Students incorrectly mix up amide hydrolysis with neutral acyl chloride hydrolysis
  - Correct: Explicitly note that alkaline hydrolysis first produces a carboxylate salt, and a separate acidification step is required to get the free carboxylic acid
- **Wrong:** Naming secondary amides as N-acyl derivatives of the amine parent
  - Why it fails: Misapplying amine naming rules instead of amide naming conventions
  - Correct: Always select the longest carbon chain containing the amide functional group as the parent, with N-alkyl substituents listed first
- **Wrong:** Claiming LiAlH₄ reduction of amides produces a primary alcohol
  - Why it fails: Confusing amide reduction with reduction of carboxylic acids or esters
  - Correct: Amide reduction converts C=O to CH₂, producing an amine with the same total number of carbon atoms as the starting amide
- **Wrong:** Drawing the amide functional group as R-CO-NH₃⁺
  - Why it fails: Mixing up neutral amide structure with ammonium salt ions
  - Correct: The neutral amide has a covalent C-N single bond with partial double bond character, no full positive charge on the nitrogen atom
- **Wrong:** Stating all amides are fully miscible with non-polar organic solvents
  - Why it fails: Ignoring the high polarity of the amide functional group
  - Correct: Only low molecular weight amides (up to 3 carbons) are miscible with water, higher molecular weight amides are insoluble in both water and non-polar solvents

## Cheatsheet

| Reaction | Reagents & Conditions | Organic Products |
| --- | --- | --- |
| Acid hydrolysis | Dilute strong acid, heat under reflux | Carboxylic acid + ammonium salt |
| Alkaline hydrolysis | Aqueous NaOH, heat under reflux | Carboxylate salt + ammonia |
| Reduction | LiAlH₄, dry ether, warm | Primary/secondary/tertiary amine |
| Dehydration | P₄O₁₀, strong heat | Nitrile (from primary amide) |

## What's next

Mastering amide chemistry completes your foundational knowledge of core carboxylic acid derivatives, and builds directly to high-weight CIE A-Level Paper 4 topics including amino acids, peptides, and condensation polymerisation. Amides are a very common intermediate in synthetic pathway questions, where you will be expected to interconvert between nitriles, carboxylic acids, and amines using the reactions covered in this module. To reinforce your understanding, practice applying these reaction rules to multi-step synthesis problems before moving to the related topics below.

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