Organic chemistry

• Hydrocarbons

  Any compound that is formed from carbon and hydrogen atoms only.
• alkanes

  general formula -$C_nH_{2n+2}$

  A group of organic compounds that react in similar ways

  Made up of single C-C bonds

  Saturated compounds

  First four are - methane, ethane, propane and butane.
• hydrocarbon properties

  the length of the carbon chain changes, the properties of the hydrocarbon change.

  • the shorter the carbon chain, the more runny the hydrocarbon is (less viscous)
  • the shorter the carbon chain, the more volatile the hydrocarbon
  • the shorter the carbon chain, the more flammable the hydrocarbon
  • the properties of hydrocarbons affect how they’re used for fuels e.g. short chain hydrocarbons with lower boiling points are used as ‘bottled gases‘
• complete combustion equation

  hydrocarbon + oxygen -> carbon dioxide + water
• crude oil

  crude oil is a fossil fuel. its formed from the remains of plants and animals, mainly plankton, that died millions of years ago and were buried in mud. over millions of years, with high temperature and pressure, the remains turn to crude oil, which can be drilled up from the rocks where its found.

  fossil fuels like coal, oil and gas are called non-renewable fuels as they take so long to make that they’re being used up much faster than they’re being formed. they are finite resources.
• fractional distillation

  crude oil is a mixture of lots of different hydrocarbons, most of which are alkanes. the different compounds in crude oil are separated by fractional distillation.

  this is how it works:

  -the oil is heated until most of it has turned into gas. the gases enter a fractionating column.

  -in the column theres a temperature gradient (hot at bottom, cooler as you go up)

  -the longer hydrocarbons have high boiling points. they condense back to liquids and drain out of column early on. the shorter hydrocarbons have lower boiling points. they condense and drain out later on
• the uses of crude oil

  • fuel for transport
  • petrochemical industry (polymers, solvents, lubricants, detergents)
• why is cracking used ?

  short-chain hydrocarbons are flammable so make good fuels and are in high demand. however long-chain hydrocarbons form thick gloopy liquids like tar which isn’t useful so a lot of the longer alkane molecules produced from fractional distillation are turned into smaller, more useful ones by the process of cracking. As well as alkanes, cracking produces alkenes. Which are used as a starting material when making lots of other compounds
• what is cracking ?

  A thermal decomposition reaction. Which is breaking molecules down by heating them. The first step is to heat long-chain hydrocarbons to vaporise them. Then the vapour is passed over a hot powdered aluminium oxide catalyst. The long-chain molecules split apart on the surface of the specks of catalyst. This is known as catalytic cracking.

  You can also crack hydrocarbons if you vaporise them, mix them with steam and then heat them to a very high temperature. This is known as steam cracking.
• alkenes

  have a double c=c bond.

  have two fewer hydrogens compared with alkanes containing the same number of carbon atoms.

  reactive

  first four alkenes - ethene, propene, butene, pentene

  general formula - $C_nH_{2n}$
• alkene burning

  combust completely with large amounts of oxygen. this produces only water and carbon dioxide.

  however if there isn’t enough oxygen in the air, they undergo incomplete combustion. you have this equation

  alkene + oxygen = carbon + carbon monoxide + carbon dioxide + water

  results in smoky yellow flame and less energy being released
• reaction of alkenes

  react in similar ways

  most of the time, alkenes react via addition reactions. the carbon-carbon double bond will open up to leave a single bond and a new atom is added to each carbon
• hydrogenation

  hydrogen can react with the double-bonded carbons to open up the double bond and form the equivalent, saturated, alkane.
• alcohols

  when alkenes react with steam, water is added across the double bond and an alcohol is formed.

  e.g - ethanol can be made by mixing ethene with steam and then passing it over a catalyst

  the conversion of ethene to ethanol is one way of making ethanol industrially. after the reaction has taken place, the reaction mixture is passed from the reactor into a condenser. ethanol and water have a higher boiling point than ethene, so both condense whilst any unreacted ethene gas is recycled back into the reactor. the alcohol can then be purified from the mixture by fractional distillation
• halogens reacting with alkenes

  alkenes will also react in addition reactions with halogens such as bromine, chlorine and iodine. the molecules formed are saturated, with the C=C carbons each becoming bonded to a halogen atom.
• Plastics

  Polymers are long molecules formed when lots of small molecules called monomers join together. This reaction is called polymerisation. It usually needs high pressure and a catalyst. Plastics are made up of polymers. They’re usually carbon based and their monomers are often alkenes.
• addition polymers

  the monomers that made up addition polymers have a double covalent bond.

  lots of unsaturated monomer molecules can open up their double bonds and join together to form polymer chains. this is called addition polymerisation. when the monomers react in addition polymerisation reactions, the only product is the polymer, so an addition polymer contains exactly the same type and number of atoms as the monomers that formed it
• alcohols general formula

  $C_nH_{2n+1}OH$

  First four - methanol, ethanol, propanol, butanol
• the properties of the first four alcohols

  -flammable

  -undergo combustion to produce carbon dioxide and water

  -soluble in water

  -solutions of alcohol and water is neutral

  -form carboxylic acids when oxidised
• alcohols used as solvent and fuels

  alcohols such as methanol and ethanol are used in solvents in industry. this is because they can dissolve most things water can dissolve, but they can also dissolve substances water can’t dissolve.

  the first four alcohols are used as fuels. burns fairly cleanly and non-smelly
• fermentation to produce ethanol

  fermentation uses a enzyme in yeast to convert sugars into ethanol. carbon dioxide is also produced. the reaction occurs in solution so the ethanol produced is aqueous.

  sugar -> ethanol + carbon dioxide

  yeast

  fermentation happens fastest at a temperature of around 37°c, in a slightly acidic solution and under anaerobic conditions.
• carboxylic acids

  functional group -COOH

  their names end in -anoic acid

  first four - methanoic acid, ethanoic acid, propanoic acid, butanoic acid.
• carboxylic acids react

  -produce salt, water and carbon dioxide

  -salts formed end in -anoate

  -dissolve in water

  -form weak acidic solutions when dissolved in water
• esters

  functional group -COO

  formed from an alcohol and carboxylic acid

  an acid catalyst is usually used

  alcohol + carboxylic acid -> ester + water
• condensation polymerisation

  involves monomers which contain different functional groups.

  the monomers react together and bonds form between them, making polymer chains.

  for each new bond that forms, a small molecule is lost. this is why its called condensation polymerisation.

  the simplest types of condensation polymers contain two different types of monomer, each with two of the same functional group.
• addition polymerisation

  • number of types of monomer - only one monomer type containing a C=C bond.
  • number of products - only one product formed
  • functional groups involved - C=C double bond in monomer
• condensation polymerisation

  • number of types of monomers - two monomer types each containing two of the same functional groups OR one monomer type with two different functional groups
  • number of products - two types of product
  • functional groups involved in polymerisation - two reactive groups on each monomer
• amino acids

  contains two different functional groups ( a basic amino group and an acidic carboxyl group)
• proteins

  amino acids can form polymers known as polypeptides via condensation polymerisation.

  the amino group of an amino acid can react with the acid group of another, and so on, to form a polymer chain. for every new bond that is formed a molecule of water is lost.

  one or more long-chains of polypeptides are known as proteins.

  polypeptides and proteins can contain different amino acids in their polymer chains. the order of the amino acids is what gives proteins their different properties and shapes
• DNA

  is found in every living thing and many viruses. it contains genetic instructions that allow the organism to develop and operate. its a large molecule that takes a double helix structure.

  DNA is made of two polymer chains of monomers called nucleotides.
• simple sugars

  sugars are small molecules that contain carbon, oxygen and hydrogen. sugars can react together through polymerisation reactions to form larger carbohydrate polymers.