Classifying organic reactions
- The reactions of organic compounds can be classified into
- Substitution
- Addition
- Combustion
Substitution
- A substitution reaction takes place when one functional group is replaced by another
- Example: Methane reacts with bromine under ultraviolet light
CH4 + Br2 → CH3Br + HBr
methane + bromine → bromomethane + hydrogen bromide
Addition
- An addition reaction takes place when two or more molecules combine to form a larger molecule with no other products
- Example: Bromine will react with ethene and the bromine molecule will react and add across the double bond of the ethene
C2H4 + Br2 → C2H4Br2
ethene + bromine → dibromoethane
Combustion
- This is the scientific term for burning. In a combustion reaction, an organic substance reacts with oxygen to form carbon dioxide (or carbon monoxide if incomplete combustion) and water.
- Example: Alkenes burn when heated in air of oxygen
- If there is an unlimited supply of air / oxygen, the products are carbon dioxide and water
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- This is termed complete combustion
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CH4 + 2O2 → CO2 + 2H2O
C3H8 + 5O2 → 3CO2 + 4H2O
- If there is a limited supply of air / oxygen, the products are carbon monoxide and water
- This is termed incomplete combustion
CH4 + O2 → CO + 2H2O