Each organic family has a small set of reactions. Learn each one together with its reagent, its condition and what you see.
This lesson is part of SPM Chemistry carbon compounds. It assumes you can name compounds from naming and drawing organic structures.
What are the core reactions?
| Family | Reaction | Reagent and condition | What you see or get |
|---|---|---|---|
| Alkane | Complete combustion | excess oxygen | carbon dioxide and water |
| Alkane | Substitution | chlorine, sunlight | hydrogen replaced by chlorine |
| Alkene | Addition of bromine | bromine water | brown colour disappears |
| Alkene | Hydration | steam, phosphoric acid, high temperature and pressure | alcohol |
| Alcohol | Oxidation | acidified KMnO₄ or K₂Cr₂O₇, heat | carboxylic acid |
| Alcohol | Dehydration | heated porcelain chips or aluminium oxide | alkene and water |
| Acid + alcohol | Esterification | concentrated H₂SO₄, heat | ester and water |
Worked example 1: combustion
Write the complete combustion of propane, C₃H₈. The products are CO₂ and H₂O.
Carbon: 3 CO₂. Hydrogen: 4 H₂O. Oxygen on the right is 6 + 4 = 10, so 5 O₂.
C₃H₈ + 5O₂ → 3CO₂ + 4H₂O
Worked example 2: addition across a double bond
Ethene reacts with bromine. The two bromine atoms add across the C=C, and one product forms.
CH₂=CH₂ + Br₂ → CH₂Br–CH₂Br
Observation: the brown colour of bromine water disappears. Compare the wrong version CH₂=CH₂ + Br₂ → CH₂=CHBr + HBr, which is substitution and gives two products.
Worked example 3: oxidation and esterification
C₂H₅OH + 2[O] → CH₃COOH + H₂O. The purple acidified potassium manganate(VII) turns colourless.
CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O. The product is ethyl ethanoate, which has a sweet smell.
The mistake that loses marks
A student writes C₂H₄ + H₂O → C₂H₅OH and leaves out the conditions. The equation is balanced, but the marks for the reagent and condition are lost.
For every reaction, write the equation, then the conditions above or below the arrow. Then check the observation when the question asks for one.
Check yourself
Write the equation for the complete combustion of ethene, and state what happens when ethene is shaken with bromine water.
Answer
C₂H₄ + 3O₂ → 2CO₂ + 2H₂O. Oxygen check: 6 on the left, and 4 + 2 = 6 on the right.
With bromine water, the brown colour disappears, because bromine adds across the double bond to form 1,2-dibromoethane.
What to study next
Chain these reactions together in planning a reaction pathway from given compounds. Test the whole set with the practice questions.
Use the mistake log and paper-error review to track missing conditions. For a teacher to go through your equations with you, see online one-to-one Chemistry tuition.