Organic chemistry is worth about 30 marks in Paper 2. Thirty marks from one topic that follows clear, logical rules.
The problem? Students treat it like a memorisation nightmare. They try to cram every reaction, every name, every functional group the night before the exam. That does not work. Organic chemistry is a system. Learn the system and the names write themselves. Learn the patterns and the reactions make sense.
This post teaches you the system.
In This Post You Will Learn
✓ The IUPAC naming rules step by step so you can name any molecule
✓ The functional groups you must be able to identify and draw
✓ The key reactions: combustion, substitution, addition, elimination, esterification
✓ How to identify isomers and draw structural formulas
✓ The difference between saturated and unsaturated compounds
✓ How the NSC exam tests organic chemistry every year
The Homologous Series You Must Know
A homologous series is a family of compounds with the same general formula and similar properties.
| Series | General Formula | Functional Group | Example |
|---------------|-----------------|-------------------|------------------|
| Alkanes | CnH(2n+2) | None (C-C only) | CH₄ (methane) |
| Alkenes | CnH(2n) | C=C double bond | C₂H₄ (ethene) |
| Alkynes | CnH(2n-2) | C≡C triple bond | C₂H₂ (ethyne) |
| Alcohols | CnH(2n+1)OH | -OH | CH₃OH (methanol) |
| Carboxylic acids| CnH(2n+1)COOH | -COOH | CH₃COOH |
| Esters | - | -COO- | Methyl ethanoate |
| Aldehydes | - | -CHO | Ethanal |
| Ketones | - | -CO- (middle) | Propanone |Saturated vs unsaturated:
Saturated = only single bonds (alkanes). All carbon bonds are "full."
Unsaturated = has a double or triple bond (alkenes, alkynes). Can still add more atoms.
IUPAC Naming: The Step-by-Step Method
Step 1: Find the Longest Carbon Chain
This gives you the base name.
| Carbons | Prefix |
|---------|---------|
| 1 | meth- |
| 2 | eth- |
| 3 | prop- |
| 4 | but- |
| 5 | pent- |
| 6 | hex- |
| 7 | hept- |
| 8 | oct- |Step 2: Identify the Functional Group for the Suffix
| Functional Group | Suffix |
|--------------------|------------|
| Alkane (C-C) | -ane |
| Alkene (C=C) | -ene |
| Alkyne (C≡C) | -yne |
| Alcohol (-OH) | -ol |
| Carboxylic acid | -oic acid |
| Ester | -oate |
| Aldehyde | -al |
| Ketone | -one |Step 3: Number the Chain
Number from the end nearest to the functional group. It gets the lowest possible number.
Step 4: Name the Branches
| Branch | Prefix |
|----------|---------|
| -CH₃ | methyl |
| -C₂H₅ | ethyl |
| -Cl | chloro |
| -Br | bromo |Step 5: Put It Together
Format: [branch position]-[branch name][base]-[functional group position]-[suffix]
Example: CH₃ - CH(CH₃) - CH₂ - OH
Longest chain = 3 carbons = prop-
OH on carbon 1. Branch (CH₃) on carbon 2.
Name: 2-methylpropan-1-ol
Key Organic Reactions
Combustion
Every organic compound burns in oxygen.
Complete: hydrocarbon + O₂ → CO₂ + H₂O
Incomplete (not enough O₂): produces CO or C (soot).
Addition Reactions (Unsaturated Only)
Only alkenes/alkynes can do this. The double bond opens up.
| Reaction | Equation Example | Conditions |
|------------------|-------------------------------|---------------------|
| Hydrohalogenation | CH₂=CH₂ + HBr → CH₃CHBr | None needed |
| Hydration | CH₂=CH₂ + H₂O → CH₃CH₂OH | H₂SO₄ catalyst |
| Hydrogenation | CH₂=CH₂ + H₂ → CH₃CH₃ | Pt or Ni catalyst |
| Halogenation | CH₂=CH₂ + Br₂ → CH₂BrCHBr | None needed |Substitution Reactions (Saturated Only)
Alkanes undergo substitution. An atom replaces another atom.
CH₄ + Cl₂ → CH₃Cl + HCl (UV light or heat needed)
Elimination Reactions
Remove atoms to form a double bond. The reverse of addition.
Dehydration: alcohol → alkene + water (concentrated H₂SO₄, heat)
Dehydrohalogenation: haloalkane + NaOH → alkene + water + NaCl (NaOH in ethanol, heat)
Esterification
Alcohol + carboxylic acid → ester + water (H₂SO₄ catalyst)
CH₃OH + CH₃COOH → CH₃COOCH₃ + H₂O
How to name an ester: Alcohol part first (change -ol to -yl). Acid part second (change -oic acid to -oate). methanol + ethanoic acid = methyl ethanoate.
For full live lessons on organic chemistry, see our Grade 12 Physical Science tuition page.
Isomers: Same Formula, Different Structure
Example: C₄H₁₀ has two structural isomers:
Butane: CH₃-CH₂-CH₂-CH₃ (straight chain)
2-methylpropane: CH₃-CH(CH₃)-CH₃ (branched)
Same molecular formula. Different arrangement. Different properties.
Functional group isomers: Same formula, different functional group.
C₂H₆O can be ethanol (CH₃CH₂OH) or dimethyl ether (CH₃OCH₃).
If you need mole calculations for reaction equations, read Stoichiometry Grade 12 - Mole Calculations Made Easy.
Common Mistakes Students Make
- Numbering the chain from the wrong end
Always number from the end that gives the functional group the lowest number. Students number from the left by habit and get position numbers wrong.
- Choosing the wrong longest chain
The longest chain might go around a corner if there are branches. It is not always drawn in a straight line.
- Confusing addition and substitution reactions
Addition = double bond opens. Only for alkenes/alkynes.
Substitution = atom replaces atom. Only for saturated compounds.
- Forgetting reaction conditions
The DBE always asks for conditions. Forgetting "H₂SO₄ catalyst" or "UV light" costs marks.
| Reaction | Conditions |
|--------------------|--------------------------------|
| Combustion | Ignite / heat + O₂ |
| Substitution | UV light or heat |
| Addition (hydration)| H₂SO₄ catalyst, heat |
| Addition (hydrogenation)| Pt or Ni catalyst |
| Elimination | Concentrated H₂SO₄, heat |
| Esterification | H₂SO₄ catalyst, heat |- Drawing structures with wrong bonding
Every C must have 4 bonds. Every O must have 2. Every H must have 1. If bonds do not add up, your structure is wrong.
How This Topic Appears in the NSC Exam
Organic chemistry appears in Paper 2, usually as Question 10 or Question 11.
It carries around 30 marks.
| Question Type | Marks |
|---------------------------------|-------|
| IUPAC naming (give or identify) | 3-4 |
| Identify functional group/series | 1-2 |
| Identify reaction type | 2 |
| Write balanced reaction equation | 3-4 |
| Draw structural isomers | 4 |
| Physical property comparison | 3-4 |
| Reaction conditions | 2 |
| TOTAL | ~30 |In the 2023 NSC exam, organic chemistry included IUPAC naming, identifying functional groups, writing an esterification reaction, and explaining boiling point differences based on intermolecular forces.
The naming marks are free if you know the system. The reaction type marks are free if you know the rule. Practise 3 to 4 past paper organic questions and you will be ready.
Want live lessons covering organic chemistry and every Paper 2 topic?
A-Game Academy teaches Grade 12 Physical Science online via Zoom. Small classes, max 15 students. Weekly past paper practice. Study notes for every topic.
R799/month or try a trial week for R199 with no commitment.
👉 Get your spot at A-Game Academy
0 comments