Organic Chemistry: Nitrogen Compounds

Revise Organic Chemistry: Nitrogen Compounds for Chemistry 5 (IAL) WCH15 (A2 Level) — revision notes and instant AI marking.

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Edexcel IAL Chemistry · Organic Chemistry

Nitrogen Compounds: Amines, Amides & Amino Acids

🧠 The Big Idea: Nitrogen's lone pair of electrons is the key to everything in this chapter — it makes amines basic (they grab protons), it makes nitrogen a great nucleophile (it attacks electron-poor carbons to build amides and bigger amines), and when amino acids use both their amine AND acid groups to link up, they build the proteins your body is made of.

📋 Summary — What This Chapter Covers

Amines = ammonia (NH₃) with one or more H's swapped for alkyl/aryl groups. Classified as primary, secondary, tertiary based on how many H's on the nitrogen have been replaced.
Amine basicity depends on how available the nitrogen's lone pair is — alkyl groups push electron density on (more basic); benzene rings pull it into the ring via delocalisation (less basic).
Amines react with acids (→ salts), acyl chlorides (→ amides), halogenoalkanes (→ bigger amines, eventually quaternary salts), and Cu²⁺ ions (→ coloured complexes, like ammonia).
Primary amines are made by reacting halogenoalkanes with excess ammonia, or by reducing nitriles (LiAlH₄ or H₂/Ni catalyst).
Phenylamine is made from nitrobenzene in a 2-stage reduction: Sn/HCl reflux → phenylammonium ion, then NaOH → phenylamine. It's a weaker base than ammonia because the lone pair delocalises into the ring.
Amides (–CONR₂) form from acyl chlorides + ammonia/amines via condensation (addition-elimination), releasing HCl.
Condensation polymers — polyesters (ester links, from diols + diacids) and polyamides (amide links, from diamines + diacids) — form by repeatedly eliminating small molecules (usually H₂O or HCl).
Amino acids are amphoteric (both acidic –COOH and basic –NH₂). In solution they form zwitterions — one molecule, two opposite charges.
The isoelectric point is the pH where the amino acid is a perfectly neutral zwitterion (equal + and − charge).
Amino acids link via peptide bonds (a type of amide bond) to form dipeptides, tripeptides, and eventually polypeptides/proteins.

1. Amines, Amides & Amino Acids — The Family

Think of ammonia (NH₃) as the "parent" molecule for this whole chapter. Everything here is basically ammonia with some of its hydrogens swapped out for carbon-based groups:

H R R R | | | | H-N-H H-N-H R-N-H R-N-R | | | | H H R R AMMONIA PRIMARY SECONDARY TERTIARY AMINE AMINE AMINE (0 H's (1 H (2 H's (3 H's replaced) replaced) replaced) replaced)

⚠️ Classic Trap

This classification is NOT the same as primary/secondary/tertiary alcohols or haloalkanes! For alcohols and haloalkanes, you look at the carbon the OH/halogen is attached to. For amines, you look at how many hydrogens on the nitrogen have been replaced. A carbon attached to three other carbons can still be part of a "primary" amine if only one H on the N is swapped.