Great! Let’s dive into O Level Organic Chemistry. This lesson will cover the basics,
commonly required in syllabi such as ZIMSEC or Cambridge. If you're ready, here's how we'll
go:
📚 O Level Organic Chemistry: Introduction Lesson
🔹 1. What is Organic Chemistry?
Organic Chemistry is the study of carbon-containing compounds, especially those that also
contain hydrogen. It excludes oxides of carbon (e.g. CO₂, CO) and carbonates.
🔹 2. Characteristics of Organic Compounds





Made mainly of carbon and hydrogen (sometimes oxygen, nitrogen, halogens).
Mostly covalent compounds.
Often insoluble in water, but soluble in organic solvents.
Have low melting and boiling points compared to inorganic compounds.
Burn in air to form CO₂ and H₂O (combustion).
🔹 3. Hydrocarbons
Hydrocarbons are compounds made of only carbon and hydrogen.
➤ Types of Hydrocarbons:
Type
Bond Type
Example Formula
Methane CH₄
Alkanes Single bonds
Alkenes At least one double bond Ethene C₂H₄
Alkynes At least one triple bond Ethyne C₂H₂
🔹 4. Homologous Series
A homologous series is a group of compounds with:


Same general formula
Same functional group


Similar chemical properties
Gradation in physical properties (e.g. boiling point)
🔸 Examples:



Alkanes: General formula = CₙH₂ₙ₊₂
Alkenes: CₙH₂ₙ
Alcohols: CₙH₂ₙ₊₁OH
🔹 5. Naming Organic Compounds (IUPAC Rules)
Let’s take Alkanes as an example.
➤ Prefix + Suffix:


Prefix = Number of carbons (meth-, eth-, prop-, but-, etc.)
Suffix = Type of compound (-ane for alkanes, -ene for alkenes, etc.)
No. of C atoms Prefix Example
1
meth- methane
2
eth- ethane
3
prop- propane
4
but- butane
🔹 6. Isomerism
Isomers are compounds with the same molecular formula but different structural formulas.
Example:

Butane (C₄H₁₀) has:
o Straight chain (butane)
o Branched chain (methylpropane)
🔹 7. Reactions of Organic Compounds
🔸 Combustion (burning)
CH4+2O2→CO2+2H2OCH₄ + 2O₂ → CO₂ + 2H₂O (complete combustion)
🔸 Addition (Alkenes)
Ethene + Bromine → 1,2-dibromoethane
Test for unsaturation: bromine water turns colourless.
🔸 Substitution (Alkanes)
Methane + Chlorine → Chloromethane + HCl (in presence of UV light)
🔸 Oxidation of Alcohols
Ethanol + [O] → Ethanoic acid + H₂O
(using acidified potassium dichromate)
🔹 8. Functional Groups
Functional Group Example Group Formula
Alkane
CH₄
—
Alkene
C₂H₄
C=C
Alcohol
C₂H₅OH —OH
Carboxylic Acid CH₃COOH —COOH
📝 Practice Questions
1.
2.
3.
4.
5.
Name the first five alkanes.
Write the structural formula of butene.
State one test for alkenes.
Give two isomers of pentane.
Write a balanced equation for the combustion of ethane.
Would you like the next lesson on reactions of specific organic families, exam-style
questions, or help with specific topics (e.g., polymers, alcohols, or carboxylic acids)?
📘 Lesson 2: Reactions of Organic Compounds
🔹 1. Reactions of Alkanes (CₙH₂ₙ₊₂)
Alkanes are saturated hydrocarbons—only single bonds.
� Common Reaction: Substitution


Happens in the presence of UV light.
A hydrogen atom is replaced by a halogen (e.g., chlorine or bromine).
Example:
CH4+Cl2→UV lightCH3Cl+HClCH₄ + Cl₂ \xrightarrow{UV~light} CH₃Cl + HClCH4+Cl2
UV lightCH3Cl+HCl
🔹 2. Reactions of Alkenes (CₙH₂ₙ)
Alkenes are unsaturated hydrocarbons—contain a double bond (C=C).
� Common Reaction: Addition
Alkenes can react with:



Hydrogen (H₂) – hydrogenation
Halogens (Br₂, Cl₂) – halogenation
Steam (H₂O) – hydration
Example:
Ethene + Bromine → 1,2-dibromoethane
C2H4+Br2→C2H4Br2C₂H₄ + Br₂ → C₂H₄Br₂C2H4+Br2→C2H4Br2
✅ Test for unsaturation: Bromine water goes from orange to colourless.
🔹 3. Reactions of Alcohols (CₙH₂ₙ₊₁OH)
� (a) Combustion
Burn in air to produce CO₂ and H₂O.
C2H5OH+3O2→2CO2+3H2OC₂H₅OH + 3O₂ → 2CO₂ + 3H₂OC2H5OH+3O2→2CO2+3H2O
� (b) Oxidation to Acids

Using acidified potassium dichromate (K₂Cr₂O₇).


Turns from orange to green.
Ethanol becomes ethanoic acid.
C2H5OH+[O]→CH3COOH+H2OC₂H₅OH + [O] → CH₃COOH + H₂OC2H5OH+[O]→CH3
COOH+H2O
� (c) Reaction with Sodium


Produces hydrogen gas and a salt.
Effervescence observed.
C2H5OH+Na→C2H5ONa+12H2↑C₂H₅OH + Na → C₂H₅ONa + \frac{1}{2}H₂↑C2H5
OH+Na→C2H5ONa+21H2↑
🔹 4. Reactions of Carboxylic Acids (CₙH₂ₙO₂)
� (a) Reaction with Carbonates


Produces a salt + CO₂ + H₂O.
Effervescence due to CO₂ gas.
CH3COOH+Na2CO3→2CH3COONa+CO2+H2OCH₃COOH + Na₂CO₃ → 2CH₃COONa + CO₂
+ H₂OCH3COOH+Na2CO3→2CH3COONa+CO2+H2O
� (b) Reaction with Alcohols (Esterification)


Produces ester + water.
Needs concentrated sulfuric acid as a catalyst.
Example:
CH3COOH+C2H5OH→H2SO4CH3COOC2H5+H2OCH₃COOH + C₂H₅OH
\xrightarrow{H₂SO₄} CH₃COOC₂H₅ + H₂OCH3COOH+C2H5OHH2SO4CH3COOC2H5+H2O
(Ethanoic acid + ethanol → ethyl ethanoate)
� Summary Table
Compound Type Main Reaction
Test or Observation
Alkane
Substitution (UV) Slow, needs UV
Alkene
Addition
Decolorizes Br₂
Compound Type Main Reaction
Test or Observation
Alcohol
Oxidation / Na
Orange to green / fizzing
Acid
Carbonates / Esters CO₂ gas / sweet smell
📝 Quick Quiz
1.
2.
3.
4.
5.
What is observed when ethanol is heated with acidified potassium dichromate?
What type of reaction is alkene + hydrogen?
Write the balanced equation for the combustion of propane.
What is the name of the ester formed from methanol and propanoic acid?
Name a visible sign of a reaction between ethanoic acid and sodium carbonate.
Excellent! Let's keep the momentum going with:
✅ Lesson 3: Isomerism & Functional Groups
🔹 1. Isomerism
Isomers are compounds with the same molecular formula but different structural formulae.
➤ Types of Isomerism at O Level:
1. Structural Isomerism – atoms are connected differently.
o Chain isomerism: different carbon chain (e.g., butane vs methylpropane).
o Position isomerism: functional group in different positions (e.g., butan-1-ol vs
butan-2-ol).
o Functional group isomerism: different functional group (e.g., alcohol vs ether –
not usually tested at O Level).
✅ Example:
C₄H₁₀


Butane: CH₃–CH₂–CH₂–CH₃
Methylpropane: CH₃–CH(CH₃)–CH₃
🔹 2. Functional Groups
A functional group is the part of a molecule responsible for its chemical reactions.
Compound Type Functional Group Example
Formula
C=C
Ethene
C₂H₄
Alkene
–OH
Ethanol
C₂H₅OH
Alcohol
Ethanoic acid CH₃COOH
Carboxylic Acid –COOH
–COO–
Ethyl ethanoate CH₃COOC₂H₅
Ester
🔹 Naming Rules Recap (IUPAC)



Longest carbon chain = root name (meth-, eth-, prop-, etc.)
Suffix = functional group (-ane, -ene, -ol, -oic acid)
Number the chain to give the lowest number to the functional group
✅ Lesson 4: Polymers
🔹 1. What are Polymers?
Polymers are large molecules made from small units (monomers) joined together.
There are two types of polymerisation:
🔸 A. Addition Polymerisation



From alkenes.
Double bonds open up to form long chains.
Only one type of monomer is used.
Example:
Ethene → Polyethene
nC2H4→(−CH2–CH2−)nnC₂H₄ → (-CH₂–CH₂-)ₙ
🔍 Characteristics:

No by-products

Used in plastics (polyethene, polystyrene, PVC)
🔸 B. Condensation Polymerisation


Two monomers with different functional groups.
Produces a small molecule as by-product (often water or HCl).
Example:
Dicarboxylic acid + Diol → Polyester + Water
🔍 Characteristics:


By-product formed (e.g. water)
Used to make nylon, terylene
🔹 2. Natural vs Synthetic Polymers
Type
Examples
Natural Proteins, starch, cellulose
Synthetic Nylon, polyester, PVC
🔹 3. Environmental Impact


Non-biodegradable plastics cause pollution.
Solutions include:
o Recycling
o Using biodegradable plastics
o Incineration with energy recovery
📝 Exam Practice Questions + Marking Scheme
Section A: Multiple Choice
1. Which compound is an alkene?
A. C₂H₆
B. C₂H₄
C. CH₃OH
D. CH₄
✅ Answer: B
2. Which test confirms the presence of an alkene?
A. Red litmus
B. Limewater
C. Bromine water
D. Benedict's solution
✅ Answer: C
3. The monomer of polyethene is:
A. Ethanol
B. Ethanoic acid
C. Ethene
D. Propene
✅ Answer: C
Section B: Short Answer
4. Draw and name two isomers of C₄H₁₀.
✅ Marking Scheme:


Butane: ✓ for correct structure/name
Methylpropane: ✓ for correct structure/name
[2 marks]
5. Write an equation for the complete combustion of butane.
2C4H10+13O2→8CO2+10H2O2C₄H₁₀ + 13O₂ → 8CO₂ + 10H₂O
✅ Marking Scheme:


Balanced equation: 1 mark
Correct products (CO₂ + H₂O): 1 mark
[2 marks]
6. State one environmental problem caused by addition polymers.
✅ Sample Answer: They are non-biodegradable and cause land and water pollution.
[1 mark]
Section C: Structured Questions
7. Ethanol can be oxidised to ethanoic acid.
a) Name a suitable oxidising agent.
✅ Acidified potassium dichromate – 1 mark
b) State a visible observation during this reaction.
✅ Orange to green colour change – 1 mark
c) Write a balanced equation.
C2H5OH+[O]→CH3COOH+H2OC₂H₅OH + [O] → CH₃COOH + H₂O
✅ Balanced equation – 2 marks
[Total: 4 marks]
8. The diagram below shows the polymerisation of propene.
a) Name the type of polymerisation.
✅ Addition – 1 mark
b) Draw the repeating unit of the polymer.
✅ Correct structure – 2 marks
c) State one use of this polymer.
✅ E.g., plastic ropes or crates – 1 mark
[Total: 4 marks]
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