Edexcel International A Level Chemistry

Topic 19: Organic Nitrogen Compounds: Amines, Amides, Amino Acids and Proteins

Amines, amides, amino acids and the polymers built from them. One atom, nitrogen, with one lone pair, explains the base behaviour, the reactions and the shapes of the molecules in this topic.

The one idea

Nitrogen in an amine, –NH₂, has a lone pair of electrons. Almost everything in this topic is that lone pair doing something:

1. Accepting H⁺. The amine is a base: it makes water alkaline and forms salts with acids.
2. Attacking a δ+ carbon. The amine is a nucleophile: it reacts with halogenoalkanes and acyl chlorides.
3. Donating to a metal ion. The amine is a ligand: it gives a complex with copper(II).
4. Being pulled away. In phenylamine the lone pair spreads into the ring, so every one of the three jobs above is weaker.

The second half of the topic joins molecules through amide links, –CO–NH–. The same link makes nylon, and it makes proteins. Hydrogen bonds between N–H and C=O groups explain the properties of both.

How to use these notes

• Pages 1 to 6 are about amines, amides and the preparations. Pages 7 to 9 are about polymers. Pages 10 to 12 are about amino acids. Page 13 joins the routes together and shows how reagent questions are marked.
• Every explanation question about basicity has the same chain: structure, then availability of the lone pair on nitrogen, then ability to accept H⁺. Learn the chain, not a slogan.
• Mark schemes look for exact reagents and conditions: concentrated hydrochloric acid, dry ether, excess ammonia in ethanol, below 10 °C. Each page shows where these appear.
• Each page ends with questions and fully worked answers. Cover the answers, try the questions, then mark yourself.
• Use the topic on a page the night before an exam.

Relative atomic masses are the Edexcel IAL periodic table values to one decimal place: H 1.0, C 12.0, N 14.0, O 16.0, Cl 35.5, Br 79.9. Topic 18 covers nitration of benzene, which gives the nitrobenzene used on page 6; Topic 15 covers chirality, which page 11 applies to amino acids.

Pages

1. Names and formulae

   Amines, amides and amino acids are named from the carbon chain plus one nitrogen group. Learn the three groups, the naming rules, and what a displayed and a skeletal formula must show.

   15 min 19.1

2. Amines and water

   Short amines mix with water because they hydrogen bond to it, and they make the solution alkaline because the nitrogen lone pair accepts H⁺. How well it does so depends on what is attached to the nitrogen.

   15 min 19.2(i)19.3

3. Salts and complex ions

   The same lone pair that makes an amine a base lets it join H⁺ to make a salt, and join a copper(II) ion to make a complex. Both reactions use the lone pair as an electron pair donor.

   12 min 19.2(ii)19.2(v)

4. Making and extending amines

   A halogenoalkane and ammonia give a primary amine, but the amine can react again and again. Reducing a nitrile gives only the primary amine. The same substitution is why butylamine reacts with halogenoalkanes.

   15 min 19.2(iii)19.4(i)19.4(ii)

5. Acyl chlorides and amides

   An acyl chloride reacts with ammonia to give an amide, and with a primary amine to give an N-substituted amide. The reaction is fast at room temperature and gives off hydrogen chloride.

   12 min 19.2(iv)19.7

6. Phenylamine and azo dyes

   Reduce nitrobenzene with tin and concentrated hydrochloric acid to make phenylamine. Keep phenylamine cold with nitrous acid to make a diazonium ion, then couple it with phenol to make a coloured azo dye.

   15 min 19.519.6

7. Polyamides and proteins

   Condensation polymers join monomers with the loss of a small molecule each time. When the link formed is an amide link, the polymer is a polyamide. Nylon is made from a diamine and a diacid, and proteins from amino acids.

   15 min 19.8(i)19.9

8. Addition polymers

   In addition polymerisation the C=C bond of the monomer opens and nothing is lost. Poly(propenamide) and poly(ethenol) follow the same pattern as poly(ethene). Draw the two chain carbons in brackets, with the side group attached.

   10 min 19.8(ii)19.9

9. Hydrogen bonding in polymers

   Hydrogen bonds between N–H and C=O groups on neighbouring chains make polyamides strong. Hydrogen bonds between the –OH groups of poly(ethenol) and water make it dissolve, which is why it is used for soluble laundry bags and liquid-detergent capsules.

   10 min 19.10

10. Amino acids as acids and bases

    An amino acid has a basic –NH₂ group and an acidic –COOH group in the same molecule, so it exists as a zwitterion and reacts with both acids and alkalis. Its form depends on the pH.

    12 min 19.11(i)

11. Amino acids and polarised light

    Most amino acids have a chiral carbon, so a single enantiomer rotates the plane of plane-polarised monochromatic light. Glycine has no chiral carbon and does not, and a racemic mixture shows no net rotation.

    12 min 19.11(ii)

12. Peptide bonds

    Amino acids join by condensation to form peptide links, and adding water back breaks them. To show which amino acids were joined, hydrolyse the peptide with acid, then identify the amino acids by paper chromatography with ninhydrin.

    15 min 19.11(iii)

13. Routes and exam technique

    Put the reactions together into synthesis routes, learn what you see at each step, and learn the exact wording that reagent, condition and observation questions are marked on.

    15 min 19.2(iv)19.2(v)19.4(i)19.4(ii)19.519.619.7

Also in this topic: Topic 19 on a page

Spec checklist

Every point you can be examined on in this topic, and where it is explained. Tick them off as you go.