Organic chemistry

• Alkenes


  Unsaturated hydrocarbons
• Alkenes


  • Have a C=C double bond
  • General formula CnH2n
• Double bond


  Two carbon atoms bonded together by a double bond
• First three alkenes


  • Ethene (C2H4)
  • Propene (C3H6)
  • Butene (C4H8)
• Butene has two different structural isomers
• Addition reaction of alkenes with bromine

  Bromine splits the double bond and adds to each carbon
• Addition reactions only form one product
• Bromine water test


  Decolourises for alkenes, no reaction for alkanes
• Alkanes


  Saturated hydrocarbons
• Alkanes


  • General formula CnH2n+2
  • Only single bonds between carbon atoms
• First four alkanes


  • Methane (CH4)
  • Ethane (C2H6)
  • Propane (C3H8)
  • Butane (C4H10)
• Halogenation of alkanes


  1. Substitution reaction under UV light

  2. Replaces hydrogen with halogen
• Empirical formula


  Simplified formula showing the simplest whole number ratio of atoms
• Molecular formula


  Formula showing the actual number of atoms present
• Structural isomers


  Molecules with the same molecular formula but different structural formulas
• Homologous series


  Groups of organic compounds with the same functional group and similar properties
• Functional group


  Groups of atoms that give compounds similar properties and reactions
• General formula for alkene homologous series

  • CnH2n
• Ethene has the molecular formula C2H4
• First four alkanes


  • Methane
  • Ethane
  • Propane
  • Butane
• Crude oil is a naturally formed mixture of hydrocarbons
• Fractional distillation of crude oil

  1. Crude oil is heated and vapourised

  2. Vapours condense at different heights in the fractionating column based on boiling points

  3. Fractions with similar boiling points are collected
• Main fractions from crude oil

  • Refinery gases (e.g. butane)
  • Petrol/gasoline
  • Kerosene
  • Diesel
  • Lubricating oils
  • Bitumen
• As hydrocarbon molecules get longer


  They become less flammable, have higher boiling points, and are more viscous
• Combustion of hydrocarbon fuels

  1. Fuel reacts with oxygen to release heat and light energy

  2. With unlimited oxygen, produces CO2 and H2O

  3. With limited oxygen, produces CO and H2O (less energy released)
• Carbon monoxide


  Colourless, odourless gas that replaces oxygen in the blood, leading to tissue damage
• Formation of nitrogen oxides in engines

  At high temperatures, nitrogen and oxygen from air undergo an endothermic reaction to form nitrogen oxides
• Formation of sulfur dioxide from burning fuels

  1. Sulfur impurities in fuels are oxidised to form sulfur dioxide

  2. Sulfur dioxide dissolves in rainwater to form sulfuric acid, causing acid rain
• Thermal cracking of long-chain alkanes

  1. Long alkanes are heated and vaporised

  2. The vapour passes over a powdered aluminium oxide catalyst

  3. The long alkanes split into shorter alkanes and alkenes
• Cracking is necessary to match supply and demand for different hydrocarbon fractions, and to produce useful alkenes
• Crude oil


  Over one of years, high temperatures and pressures cause the buried remains of plants and animal to fum into grade of. Then we come along and drill it up.
• Crude oil separation into different hydrocarbon fractions

  1. The oil is heated until most of it has burned into gas

  2. The gaseous substances go through a fractionating column

  3. The longer hydrocarbons have high boiling points and condense and drain out early

  4. The shorter hydrocarbons have lower boiling points and condense and drain out later

  5. Bubbles in the fractionating column stop the separated liquids from running back down the column
• Fractions from crude oil

  • Refinery gas
  • Gasoline
  • Kerosene
  • Diesel fuel
  • Fuel oil
  • Bitumen
• Just a fraction of crude oil is petrol
• Cracking


  Splitting up long-chain hydrocarbons into smaller, more useful short-chain molecules
• Cracking


  • It is a form of thermal decomposition
  • It produces alkanes which are used to make plastics
• Conditions for cracking


  1. Heat

  2. Catalyst (silica or alumina)
• Cracking in the lab

  • Vaporised alkane is heated until it breaks down when it comes into contact with the catalyst, producing a mixture of short-chain alkanes and alkenes
• Isomers


  Molecules that have the same molecular formula but different structural formulae
• Types of isomers


  • Differently shaped carbon chains
  • Functional groups in different places
  • Different functional groups