organic chem

• what is a hydrocarbon 


  any compound that is formed from carbon and hydrogen atoms only
• alkanes:

  • simplest type of hydrocarbon
  • general formula : CnH2n+2
  • saturated compunds
  • examples:
  • methane, ethane, propane, butane
• hydrocarbon properties change as the chain length gets longer
• changing hydrocarbon properties:

  • the shorter the chain the less viscous a hydrocarbon is
  • the shorter the chain the more volatile it is (i.e lower bp)
  • the shorter the chain the more flammable it is
• the complete combustion of any hydrocarbon in oxygen releases alot of energy

  hydrocarbon + oxygen --> CO2 + water (+ energy)
• what is crude oil?

  a fossil fuel

  a mixture of lots of different hydrocarbons (most of which are alkanes)

  these different components can be separated via fractional distillation
• Fractional distilation:

  • oil is heated until most of it has turned to gas, these gasses enter a fractioning column
  • in the column there is a temperature gradient (hot at the bottom, cooler at the top)
  • the longer hydrocarbons have high boiling points and shorter ones have lower boiling points so they condense at different temps
  • the crude oil mixture ends up seperated into different fractions
• what is cracking?

  splitting longer chain hydrocarbons so they are more usefull
• cracking is a thermal decomposition reaction- breaking molecules down by heating them
• catalytic cracking:

  • heat long-chain hydrocarbons to vapourise them
  • this vapour is poured over a hot powdered aluminium oxide
  • the long-chained molecules split apart on the surface of the specks of catalyst
• steam cracking:

  • vapourise long-chain hydrocarbons
  • mix them with steam
  • heat to a very high temperature
• Alkenes have a double C=C bond and are unsaturated.
• alkenes:

  • hydrocarbons which have a double bond between 2 of the carbon atoms in their chain
  • unsaturated
  • general formula: CnH2n
  • examples:
  • ethene, propene, butene, pentene
• alkenes burn with a smoky flame:

  • there is not enough oxygen in the air to allow them to burn completely leading to an incomplete combustion
  • alkene + oxygen --> carbon + carbon monoxide + CO2 + water (+ energy)
• alkenes react via addition reaction :

  • the double carbon bond will open up to leave a single bond and a new atom is added to each carbon
• what is the name for when alkenes react with hydrogen ?

  hydrogenation
• steam can react with alkenes to form alcohols

  • water is added across the double bond and an alcohol is formed
• halogens can react with alkenes

  • the molecules formed are saturated with the C=C carbons becoming bonded to a halogen atom
• polymers:

  • polymers are long molecules formed when lots of small molecules called monomers join together
  • this reaction is called polymerisation
• addition polymers are made from unsaturated monomers

  • the monomers make up addition polymers which have a double covalent bond
  • lots of unsaturated monomer molecules (e.g. ethene) can open up their double bonds and join together to form polymer chains
  • this is called addition polymerisation
• alcohols :

  • -OH functional group
  • general formula: CnH2n+1OH
  • flammable
  • examples:
  • methanol, ethanol, propanol, butanol
  • all four of these have similar properties, they are soluable in water as they have a neutral pH
  • they also react with sodium
• alcohols are used as solvents and fuels

  • the first 4 are used as fuels as they burn fairly cleanly
• ethanol can be made via fermentation

  • sugar -(yeast)--> ethanol + CO2
• carboxylic acid:

  • functional group : -COOH
  • general formula: CnH2n+1COOH
  • examples: methanoic acid, ethanoic acid, propanoic acid, butanoic acid
  • react with carbonates to form salt, water and CO2
  • the salts formed in these reactions will end in -anoate (e.g ethanoic acid and ethanoate)
• esters can be made from carboxylic acid

  • functional group: -COO-
  • formed from an alcohol and a carboxylic acid
  • an acid catalyst is usually used
  • alcohol + carboxylic -(acid catalyst)--> ester + water
• condensation polymerisation:

  • involves monomers which contain different functional groups
  • these monomers react together and bonds form between them, making polymer chains
  • for each new bond that forms, a small molecule (e.g. water) is lost
  • simplest types of condensation polymers contain 2 different types of monomer each with 2 of the same functional groups
• addition polymerisation 


  number of different monomers: only 1 monomer type containing a C=C bond

  number of products: only 1 product formed

  functional groups involved : carbon-carbon double bond in monomer
• condensation polymerisation


  number of different monomers: 2 monomer types each containing 2 of the same functional groups OR one monomer type with 2 different functional groups

  number of products : 2 ( the polymer and the smaller molecule)

  functional groups involved: 2 reactive groups on each monomer
• naturally occurring polymers:

  • amino acids
  • protiens
  • dna
  • simple sugars can form polymers
• amino acids have an amino group and a carboxyl group
• proteins are polymers of amino acids:

  • amino acids can form polymers known as polypeptides via condensation polymerisation
  • one or more long chains of polypeptides are known as proteins
• DNA molecules are made from nucleotide polymers