How to Study Organic Chemistry for IGCSE

Organic chemistry is the topic that most IGCSE Chemistry students leave until last and then panic about. It appears on every Paper 2 and Paper 4 session, typically carrying 15-20 marks across both papers. The topic has a reputation for difficulty, but most of that difficulty comes from poor study strategy. Students try to memorise individual reactions in isolation rather than learning the system that connects them. Study organic chemistry as a system and it becomes one of the most predictable parts of the exam.

Start with the framework, not the details

Before learning any reactions, build a skeleton framework of the four main homologous series at IGCSE level:

Series	Functional group	General formula	Example
Alkanes	C-C single bonds only	CnH2n+2	Methane, CH4
Alkenes	C=C double bond	CnH2n	Ethene, C2H4
Alcohols	-OH	CnH2n+1OH	Ethanol, C2H5OH
Carboxylic acids	-COOH	CnH2n+1COOH	Ethanoic acid, CH3COOH

Learn this table cold. Every organic question starts from here: identify the series, identify the functional group, and the properties and reactions follow. If you cannot identify that a molecule with a C=C double bond is an alkene within seconds, every subsequent question becomes harder.

Learn each series in four layers

For each homologous series, study in this order:

Layer 1: Identity. Name the first four members. Write their molecular and structural formulae. Identify the functional group. This is pure memory work and suits flashcards.

Layer 2: Physical properties. Boiling points increase as chain length increases (more intermolecular forces). State at room temperature changes from gas to liquid to solid. These trends follow logically from intermolecular force theory — understand the principle and you can predict properties for any member.

Layer 3: Chemical reactions. This is the largest layer. For each series, learn:

• What it reacts with
• The conditions required (catalyst, temperature, UV light)
• The products formed
• The type of reaction (addition, substitution, combustion, oxidation)

For example, alkenes undergo addition reactions: they react with bromine (test for unsaturation), with hydrogen (hydrogenation, nickel catalyst), and with steam (hydration, to produce an alcohol, phosphoric acid catalyst).

Layer 4: Connections to other series. This is where organic chemistry becomes a system. Ethene + steam → ethanol (alkene to alcohol). Ethanol + oxygen → ethanoic acid (alcohol to carboxylic acid). Ethanol + ethanoic acid → ethyl ethanoate (ester formation). These transformations link the series together, and the exam frequently asks you to trace a pathway from one compound to another.

The reaction map

Draw a single diagram that shows how the four series connect. Place the series as nodes and the reactions as arrows with conditions labelled:

• Alkene → Alcohol (addition of steam, H3PO4 catalyst, 300 degrees C)
• Alcohol → Alkene (dehydration, Al2O3 catalyst, excess)
• Alcohol → Carboxylic acid (oxidation)
• Alcohol + Carboxylic acid → Ester (condensation, H2SO4 catalyst)
• Alkene → Polymer (addition polymerisation)
• Alkene + Bromine → Dibromoalkane (addition, decolourises bromine water)

Pin this map on your wall. Refer to it after every study session. After a week, redraw it from memory. This single diagram summarises most of the extended organic syllabus for organic chemistry.

Naming compounds

IUPAC naming follows a system: the prefix tells you the chain length (meth- = 1, eth- = 2, prop- = 3, but- = 4), and the suffix tells you the functional group (-ane = alkane, -ene = alkene, -ol = alcohol, -oic acid = carboxylic acid, -anoate = ester).

Common naming mistakes on 0620:

• Writing “methene” (it does not exist — you need at least two carbons for a C=C double bond)
• Confusing ethanol (an alcohol) with ethanal (an aldehyde, not on the IGCSE syllabus)
• Forgetting that ester names have two parts: the alcohol part first, then the acid part (ethyl ethanoate, not ethanoate ethyl)

Practice by naming compounds from structural formulae and drawing structural formulae from names. This is a skill, not knowledge, and it improves with repetition.

Isomers

Extended students need to understand structural isomers: compounds with the same molecular formula but different structural formulae. For example, C4H10 can be butane (straight chain) or methylpropane (branched). The key concept is that isomers have different physical properties (different boiling points) but similar chemical properties (both are alkanes, both undergo combustion).

To draw isomers, start with the longest possible chain and then systematically shorten it by moving a carbon to a branch position. Practise with C4H10, C5H12, and C4H8 (which includes both chain isomers and the additional complication of having both alkene and cyclic structures, though cyclic compounds are beyond IGCSE).

Polymers

Polymerisation appears on almost every session. Two types at IGCSE:

Addition polymerisation: Many alkene monomers join by opening their double bonds. The repeating unit keeps all the atoms of the monomer. Poly(ethene), poly(propene), poly(chloroethene) — also called PVC. Draw the repeating unit by opening the C=C double bond and extending the bonds at each end.

Condensation polymerisation (extended only): Two different monomers join, releasing a small molecule (usually water). Nylon and polyester are examples. The repeating unit shows the linkage with the lost water atoms removed.

The most common exam mistake with polymers is drawing the repeating unit without the extending bonds at each end, or forgetting to show that the double bond has opened.

Study sequence

If you are starting organic chemistry from scratch or revising it:

1. Week 1: Framework table, naming, first four members of each series. Flashcard the functional groups and general formulae.
2. Week 2: Reactions of alkanes and alkenes. Draw the reaction map for these two series. Do past paper questions on alkenes.
3. Week 3: Reactions of alcohols and carboxylic acids. Extend the reaction map. Learn ester formation.
4. Week 4: Polymers, isomers, and the organic exam technique for answering structured questions.
5. Week 5 onward: Past paper questions exclusively. Mark against the scheme and log errors.

This five-week sequence, combined with daily flashcard review, is enough to take organic chemistry from a weak topic to a reliable source of marks.