Isomerism in Alkanes and Alkenes
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What are Isomers?
- Different compounds
- Same molecular formula
- Different structural formula
- Different boiling points
- The phenomenon is known as isomerism
What happens to the number of isomers as the number of carbon atoms increase?
The number of isomers increase as the number of carbon atoms in a molecule increase
Importance of Isomers
- Isomerism is important in petrol fuel for motorcars.
- The petrol fraction from the fractional distillation of petroleum contains a lot of straight-chain alkane molecules, such as octane.
- Car engines don't run smoothly when burning straight-chain molecules
- The engines run much better when burning branched-chain isomers
- Branched-chain isomers are more expensive.
- A cheaper alternatice was to add lead compounds
- But lead from car exhausts pollute the air as lead is a poisonous metal
- Due to pollution controls, lead is no longer used and so petrol is now more relatively expensive as they contain branched-chain alkanes.
Manufacture of Margarine
- Some foods are described as being polyunsaturated
- This means their organic molecues contain C=C bonds
- Vegetable oils are polyunsaturated
- These polyunsaturated oils are considered to be healthier to eat than saturated oils
- Margarine is made by reacting vegetable oil with Hydrogen in the presence of a nickel catalyst
- Not all C=C bonds in the vegetable oil react with hydrogen.
- The margarine is said to be partially hydrogenated.
- The more hydrogenated the margarine, the fewer C=C bonds it has and the harder it is.
The Ripening of Fruits
Unripe fruits produces small amounts of ethene, which hep it to ripen
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