Organic Chemistry

• Fuels


  • Coal
  • Natural gas
  • Petroleum
• Methane


  • The main constituent of natural gas
  • CH4
• Petroleum


  A mixture of hydrocarbons
• Separation of petroleum into useful fractions by fractional distillation

  1. Petroleum is heated in a large fraction column

  2. Different hydrocarbons with different carbon chain lengths and boiling points rise up as gases and can be collected separately
• Hydrocarbon molecules in petroleum fractions

  • Shorter molecules have lower boiling points and are less viscous (more runny)
• Uses of petroleum fractions

  • Refinery gas for bottled gas
  • Gasoline for fuel (petrol) in cars
  • Naphtha for making chemicals
  • Kerosene/paraffin for jet fuel
  • Diesel oil/gas oil for fuel in diesel engines
  • Fuel oil for fuel for ships and home heating
  • Lubricating fraction for lubricants, waxes and polishes
  • Bitumen for making roads
• Homologous series

  A 'family' of similar compounds with similar chemical properties due to the presence of the same functional group
• Homologous series


  • Similar chemical properties - undergo the same chemical reactions
  • E.g. alkenes decolourise bromine water (orange to colourless) due to the C=C, whereas alkanes do not due to the lack of C=C

  
• Compounds in a homologous series

  • Have the same general formula
  • General formulae = a type of empirical formula that represents the composition of any member of an entire class of compounds (e.g. for ethene = CnH2n)
• Structural isomerism


  Compounds with the same molecular formula exist in different forms due to different arrangements of atoms
• Alkanes


  • Generally unreactive, except in terms of burning
• Bonding in alkanes


  • Contain no C=C double bonds, therefore the carbons are saturated, because they each form 4 single bonds i.e. they form as many bonds as possible
  • They have C-C and C-H single covalent bonds
• General formula for alkanes


  CnH2n+2 e.g. ethane is C2H6
• First 4 alkanes


  • Methane
  • Ethane
  • Propane
  • Butane
• Substitution reactions of alkanes with chlorine

  1. Halogen + alkane -(UV)-> halogenoalkane + hydrogen halide

  2. e.g. Br2 + C2H6 -(UV)-> C2H5Br + HBr
• Substitution reactions of alkanes with chlorine must be in the presence of ultraviolet radiation (UV)
• Manufacture of alkenes and hydrogen by cracking

  1. Heat hydrocarbons to vaporise

  2. Pass vapours over hot catalyst (silica or alumina)

  3. Mix vapours with steam and heat to very high temperature (600-700°C) for thermal decomposition

  4. Products include shorter chain alkanes, alkenes, and hydrogen
• Alkenes


  • Addition reactions
  • Involve removal of C=C double bond
  • C=C double bond is very reactive and can easily react to form -C-C-
• Reaction of alkenes with bromine

  1. Alkene + bromine → dibromoalkane

  2. E.g. Ethene + bromine → 1,2-dibromoethane
• Reaction of alkenes with steam

  1. Alkene + steam → alcohol

  2. E.g. Ethene + steam → ethanol
• Reaction of alkenes with hydrogen

  1. Alkene + hydrogen → alkane

  2. E.g. Ethene + hydrogen → ethane
• Saturated hydrocarbons


  Contain no C=C double bonds, e.g. alkanes
• Unsaturated hydrocarbons


  Contain one or more C=C double bonds, e.g. alkenes
• Distinguishing saturated and unsaturated hydrocarbons by reaction with aqueous bromine

  1. Unsaturated hydrocarbons react with bromine, decolourising it (orange to colourless)

  2. Saturated hydrocarbons do not react with bromine, solution remains orange
• Formation of poly(ethene) by addition polymerisation


  1. Many small molecules (monomers) join together to create very large molecules (polymers)

  2. Repeat unit has the same atoms as the monomer, no other molecule is formed
• Manufacture of ethanol by fermentation

  1. Fermentation of glucose

  2. Conditions: temperature of about 30°C, anaerobic conditions (no oxygen), using enzymes in yeast

  3. Equation: glucose → ethanol + carbon dioxide
• Manufacture of ethanol by catalytic addition of steam to ethene


  1. Reacting ethene with steam

  2. Conditions: phosphoric acid catalyst, temperature of about 300°C, pressure of about 60-70 atm

  3. Equation: ethene + steam → ethanol
• Fermentation


  • Renewable raw materials
  • Warm, normal pressure (inexpensive)
  • Little energy needed
• Fermentation


  • Batch process (stop-start)
  • A lot of workers needed
  • Slow
  • Impure - needs treatment
• Steam


  • Continuous process (runs all the time)
  • Few workers needed
  • Fast
  • Pure
• Steam


  • Non-renewable raw materials
  • High temperature and pressure (expensive)
  • A lot of energy needed
• Burning of ethanol in air or oxygen (complete combustion)

  1. CH3CH2OH + 3O2 → 2CO2 + 3H2O

  2. Can be used as a fuel (this reaction produces heat energy)

  3. Burns in a good supply of oxygen
• Plastics


  • Plastic bags
  • Clingfilm
  • Buckets, other plastic tools
• Man-made fibres such as nylon and Terylene


  • Drawn into very fine fibres and woven into cloth for clothing
  • Mixed with natural fibres (e.g. cotton) to make a soft but hard-wearing cloth
• Addition polymerisation


  Involves the removal of a C=C double bond to form a -C-C- bond, joining up unsaturated molecules to form a long saturated molecule

  
• Condensation polymerisation


  • Involves the reaction of two different functional groups to form one long molecule by the removal of a small molecule, such as water H2O
  • There can be more than one monomer used (unlike addition which only uses one)

  
• Formation of the polymer product from a given alkene


  The polymer product would be a long chain of the alkene without the C=C and instead with -C....C- at the end, i.e. open branches

  
• Formation of nylon (a polyamide)

  1. Amine and carboxylic acid functional groups react, losing a small molecule - water

  2. A polyamide is formed from a monomer molecule containing two carboxylic acid groups (dicarboxylic acid) reacting with a monomer molecule containing two amine groups

  3. or a single monomer molecule with both carboxylic acid and amine functional groups

  4. -OH + -COOH -> -COO- (+H2O removed)

  
• Formation of Terylene (a polyester)

  1. A polyester is formed from a monomer molecule containing two carboxylic acid groups (dicarboxylic acid) reacting with a monomer molecule containing two alcohol groups (diol)

  2. or a single monomer molecule with both carboxylic acid and alcohol functional groups

  3. -OH + -COOH -> -COO- (+H2O removed)

  
• Polymers are large molecules built up from small units (monomers)