# Organic Nitrogen Compounds: Amines, Amides, Amino Acids and Proteins

> Edexcel International A-Level Chemistry · Edexcel IAL Chemistry
> Source: https://www.owlsprep.com/study/edexcel-ial-chemistry-u5-organic-nitrogen-compounds-amines-amides/

This guide covers all Edexcel IAL Chemistry Unit 5 content for organic nitrogen compounds, including amines, amides, amino acids, polymers, and azo dye synthesis for WCH15 exam success.

**Prerequisites:** [Halogenoalkane reactions and functional group identification](https://www.owlsprep.com/study/edexcel-ial-chemistry-u2-halogenoalkanes/); [Acyl chloride reaction chemistry](https://www.owlsprep.com/study/edexcel-ial-chemistry-u4-acyl-compounds/)

## Learning objectives

- Name amines, amides and amino acids using IUPAC rules
- Explain amine basicity trends via nitrogen lone pair availability
- Recall preparation and reaction conditions for aliphatic and aromatic amines
- Draw repeat units of addition and condensation polymers
- Describe zwitterion structure and peptide bond formation
- Recall diazotisation and azo dye synthesis steps

## Structure, Nomenclature and Basicity of Amines

**Primary Amine** — An organic compound where a nitrogen atom is covalently bonded to one alkyl/aryl group and two hydrogen atoms, with the general formula $RNH_2$

Amines are classified as primary, secondary, or tertiary based on the number of alkyl/aryl groups bonded to the nitrogen atom. IUPAC nomenclature uses the suffix -amine for the parent chain, with substituents numbered relative to the amine group. Aromatic amines have nitrogen directly bonded to a benzene ring, e.g. phenylamine ($C_6H_5NH_2$).

Amine basicity depends on the availability of the lone pair of electrons on the nitrogen atom to accept a proton from an acid: primary aliphatic amines have electron-donating alkyl groups that increase lone pair availability (stronger base than ammonia), while primary aromatic amines have the N lone pair delocalised into the benzene ring (weaker base than ammonia).

**Worked example:** Place the following compounds in order of increasing basicity: ammonia, butylamine, phenylamine. Explain your answer.

1. First, classify each compound: butylamine = primary aliphatic amine, phenylamine = primary aromatic amine.
2. Apply the basicity trend: aromatic amines < ammonia < aliphatic amines.
3. Final order: phenylamine < ammonia < butylamine. Explanation: Butylamine's alkyl group increases N lone pair availability, phenylamine's delocalised N lone pair reduces availability.

> **Exam tip:** Always link basicity directly to nitrogen lone pair availability, do not just state the trend without reasoning to gain full marks.

## Reactions and Preparation of Amines

1. Reaction with water: Forms weakly alkaline solutions, e.g. $CH_3CH_2CH_2CH_2NH_2 + H_2O \rightleftharpoons CH_3CH_2CH_2CH_2NH_3^+ + OH^-$
2. Reaction with acids: Forms ionic ammonium salts, e.g. butylamine + HCl → butylammonium chloride
3. Reaction with halogenoalkanes: Forms secondary/tertiary amines via nucleophilic substitution
4. Reaction with ethanoyl chloride: Forms an amide via elimination of HCl
5. Reaction with $Cu^{2+}$ ions: Forms deep blue complex ions, similar to ammonia

Key preparation methods for amines: Aliphatic primary amines are made by heating a halogenoalkane with excess ammonia in ethanol, or reducing nitriles with $LiAlH_4$ in dry ether. Aromatic primary amines are made by reducing nitro-compounds with tin and concentrated HCl, followed by neutralisation with NaOH to liberate the free amine.

**Worked example:** State the reagents and conditions required to prepare phenylamine from nitrobenzene.

1. First reagent: Tin (Sn) metal and concentrated hydrochloric acid, heated under reflux.
2. Second reagent: Excess sodium hydroxide solution, to neutralise the intermediate phenylammonium salt and release free phenylamine.

> **Exam tip:** Do not forget the neutralisation step for aromatic amine preparation, it is a common marking point. Full reaction mechanisms are not required for any amine reactions.

## Azo Dyes, Amides and Polymer Synthesis

**Diazotisation** — The reaction of a primary aromatic amine with nitrous acid (formed in situ from NaNO₂ and dilute HCl) at temperatures below 5°C to form a stable benzenediazonium ion salt.

Benzenediazonium ions undergo coupling reactions with phenols in alkaline conditions to form brightly coloured azo dyes, used in textiles and food colouring. Amides are formed when acyl chlorides react with amines, eliminating HCl as a byproduct.

- Addition polymers: Form from alkene monomers, no byproducts, e.g. poly(propenamide), poly(ethenol)
- Condensation polymers: Form from difunctional monomers, eliminate small molecules like $H_2O$ or HCl, e.g. nylon, proteins

**Worked example:** Draw the repeat unit of nylon-6,6, formed from 1,6-diaminohexane and hexanedioic acid.

1. Each amide bond forms by eliminating one $H_2O$ molecule between an amine and carboxylic acid group.
2. $$-NH-(CH_2)_6-NH-CO-(CH_2)_4-CO-$$
3. Add trailing bonds at each end of the repeat unit, and write the letter n outside brackets to indicate multiple repeat units.

> **Exam tip:** Poly(ethenol) is water soluble due to hydroxyl groups that form hydrogen bonds with water molecules, making it ideal for soluble hospital laundry bags.

## Amino Acids, Zwitterions and Proteins

**Zwitterion** — A dipolar ion with both a positive ammonium group ($-NH_3^+$) and negative carboxylate group ($-COO^-$), with overall neutral charge, formed by amino acids at their isoelectric point.

Amino acids have the general formula $H_2N-CH(R)-COOH$, where R is a variable side chain. All naturally occurring amino acids (except glycine) have a chiral central carbon atom, so they rotate the plane of plane-polarised light. Amino acids are amphoteric: the carboxyl group can donate a proton, and the amine group can accept a proton.

Peptide bonds ($-CONH-$) form via condensation reactions between two amino acids, eliminating one molecule of water. Long chains of amino acids linked by peptide bonds are called polypeptides, or proteins when they have a functional biological structure.

**Worked example:** Draw the zwitterion structure of alanine, where R = $CH_3$.

1. The amine group accepts a proton to become $-NH_3^+$.
2. The carboxylic acid group donates a proton to become $-COO^-$.
3. $$H_3N^+-CH(CH_3)-COO^-$$
4. Confirm the overall charge of the ion is zero.

> **Exam tip:** When drawing zwitterions, always show full charges on the nitrogen and oxygen atoms, do not omit them or you will lose marks.

## Practical Identification of Organic Nitrogen Compounds

- Amines: Turn damp red litmus paper blue (alkaline), form deep blue complex with $Cu^{2+}$ ions
- Amides: Hydrolyse with warm NaOH to release ammonia gas, which turns damp red litmus blue
- Amino acids: High melting points, soluble in water due to zwitterion formation

**Check your understanding**

1. Which test would you use to distinguish between butylamine and butanamide at room temperature?

   - Add dilute HCl
   - Test with damp red litmus paper
   - Heat with NaOH and test gas output

   *Answer:* Test with damp red litmus paper

   *Why:* Butylamine is alkaline so will turn damp red litmus blue immediately, butanamide is neutral so no change at room temperature.

> **Exam tip:** Use IR data provided in the exam to identify amide bonds (strong ~1650 cm⁻¹ absorption) and amine groups (broad ~3300-3500 cm⁻¹ absorption).

## Common pitfalls

- **Wrong:** Stating aromatic amines are stronger bases than ammonia
  - Why it fails: Forgetting delocalisation of the N lone pair into the benzene ring reduces proton acceptance ability
  - Correct: Link basicity to N lone pair availability, placing aromatic amines below ammonia in basicity order
- **Wrong:** Drawing zwitterions with uncharged $-NH_2$ and $-COOH$ groups
  - Why it fails: Zwitterions require a protonated amine and deprotonated carboxyl group for neutral dipolar structure
  - Correct: Always draw zwitterions with $-NH_3^+$ and $-COO^-$ groups, showing full charges
- **Wrong:** Including $H_2O$ or HCl in condensation polymer repeat units
  - Why it fails: Small molecules are eliminated during condensation, so they are not part of the polymer chain
  - Correct: Only include atoms remaining in the polymer chain in repeat units, with trailing bonds and n notation
- **Wrong:** Forgetting to keep diazotisation reactions below 5°C
  - Why it fails: Benzenediazonium ions decompose above 5°C to form phenol and nitrogen gas, so no azo dye forms
  - Correct: Always state diazotisation is carried out at 0-5°C using an ice bath
- **Wrong:** Confusing addition and condensation polymer formation
  - Why it fails: Addition polymers form from alkenes with no byproducts, condensation forms from difunctional monomers with small molecule elimination
  - Correct: Check for double bonds in monomers to identify addition polymers, check for two distinct functional groups for condensation polymers

## Cheatsheet

| Compound Class | Key Properties/Reactions | Key Reagents/Conditions |
| --- | --- | --- |
| Primary Aliphatic Amine | Stronger base than ammonia, forms salts/amides/complexes | Excess ammonia/ethanol, $LiAlH_4$ for nitrile reduction |
| Primary Aromatic Amine | Weaker base than ammonia, forms diazonium ions | Sn/conc HCl, heat, NaOH neutralisation |
| Amide | Forms via acylation, hydrolyses to amine + carboxylic acid | Acyl chloride + amine, warm NaOH for hydrolysis |
| Amino Acid | Amphoteric, forms zwitterions, peptide bonds | Condensation polymerisation to form proteins |
| Polymer | Addition (poly(propenamide)), condensation (nylon/proteins) | Alkene monomers (addition), diamine + diacid (condensation) |
| Azo Dye | Formed via diazotisation + phenol coupling | 0-5°C, alkaline coupling conditions |

## What's next

Now that you have mastered organic nitrogen compounds for Edexcel IAL Chemistry Unit 5, you are ready to revise full Unit 5 content including transition metals and practical assessment skills to prepare for your WCH15 exam. This topic is frequently tested in both multiple choice and structured long answer questions, so practice recalling reaction conditions and drawing structures accurately. Work through past paper questions on this topic to familiarise yourself with exam phrasing and marking scheme expectations, especially for questions asking you to explain basicity trends or draw polymer repeat units. Connect this content to earlier organic chemistry topics like functional group identification to prepare for practical unknown identification questions.

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