Organic Chemistry Alkenes Flashcards
Alkenes
Unsaturated hydrocarbons with carbon-carbon double bonds
CnH2n
Alkenes are more reactive than alkanes due to their carbon-carbon double bond
Saturated
Contains only carbon-carbon single bonds
Unsaturated
Contains carbon-carbon double bonds
Physical properties of alkenes
- Low melting and boiling points
- Insoluble in water
- Soluble in organic solvents
As it goes down the series - Melting and boiling points increase
- Viscosity increase
- Density increase
- Flammability decrease
Chemical properties of alkenes
- Combustion
2. Addition reaction
Combustion
alkene + oxygen —> carbon dioxide + water
Sootier flame than alkanes due to higher percentage of carbon
Addition reaction
An unsaturated organic compound combines with another substance to form a single new compound
Addition of hydrogen (hydrogenation)
Addition of bromine (bromination)
Addition of hydrogen (hydrogenation)
Process in which hydrogen is added to the double bond
Conditions: 200 degree celsius, nickel catalyst
alkene + hydrogen —> alkane
Important in the manufacture of margarine
Polyunsaturated
Contains many carbon-carbon double bonds in their molecules
Fats vs Oils
FATS Solids at RTP Mostly saturated fat molecules OILS Liquids at RTP Mostly unsaturated dat molecules
Addition of bromine (bromination)
Process in which bromine is added to the double bond
Test for unsaturation:
Test: Add bromine solution to the compound in a test-tube
Observation: If the reddish-brown bromine decolourises, the compound is unsaturated
Saturated: no visible change
Cracking
The breaking down of long-chain hydrocarbons into smaller hydrocarbons or hydrogen
long-chain alkanes —> short-chain alkenes + short-chain alkanes or hydrogen
Role of catalyst
Speed up reaction
Conditions of industrial catalytic cracking
high temperature, 600 degree celsius
aluminium oxide and silicon dioxide catalyst
Uses of cracking
- Produces short-chain alkenes
2. Produces hydrogen
