Topic 6 - Organic I

• A homologous series is a group of organic compounds with the same structure and the same functional groups
• General formula is a generalised formula on how to write molecular formula of organic compounds which is applicable to all compounds in a homologous series
• The three different types of isomers are:

  • Chain isomers
  • Positional isomers
  • Functional group isomers
• Positional isomers have the same chemical formula, but the functional groups are in different places
• Functional group isomers have the same chemical formula but different functional groups
• Chain isomers have the same carbon chains, but in a different structure
• There are five types of formula:

  1. Empirical formula
  2. Molecular formula
  3. Displayed formula
  4. Structural formula
  5. Skeletal formula
• Aliphatic alkenes are alkenes with one double bond with a general formula of CnH2n
• Aromatic alkenes are benzenes
• Branched alkenes do follow the general formula, however it does not apply to cyclic or alkenes with more than one double bond
• For each carbon in an alkene, 3 electrons are used in sigma bonds, leaving 1 in a p orbital that's above and below. This is a pi bond.
• Atoms cannot rotate around double carbon bonds since the p orbitals must remain in the same place making it fairly rigid
• Pi bonds are weaker than sigma bonds because the electron density is spread above and below the nucleus so the electrostatic attraction is weaker
• Alkenes are quite reactive because they have a very high electron density above and below due to the pi bond, making them more susceptible to electrophiles
• Halogenoalkanes are alkanes with one or more halogens
• Halogenoalkanes are formed under UV light through a chain reaction
• The first stage of the haloalkane chain reaction is initiation:

  • A halogen absorbs the quantum of UV light and that is enough energy to break the bond
  • Atoms are identical so split evenly, taking on one electron each from the bond - homolytic fission
  • This creates two free radicals
• Homolytic fission is when a diatomic molecule is split evenly, making two free radicals
• A free radical is a highly reactive species with an unpaired electron
• The second stage of the chain reaction forming haloalkanes is propagation

  Propagation 1:

  • The halogen free radical takes a hydrogen from the alkene, becoming a stable hydrogen halide and creating an alkene free radical

  Propagation 2:

  • The alkene free radical is also very reactive so it reacts with the halogen, creating another free radical
  • This happens thousands of times before the free radical is destroyed
• The third stage of the chain reaction for forming a haloalkene is termination:

  • This is a reaction that removes the free radicals
  • This may occur if the free radicals react with eachother
• CFCs are banned in the UK because the C-Cl bond in chlorofluorocarbon, the free radical produced acts as a catalyst that destroys the ozone layer
• Catalytic cracking needs:

  • Temperatures higher than 720K
  • Pressure of higher than 1atm
  • Zeolite catalyst
• Zeolite catalysts are a honeycomb structure in order to have an enormous surface area
• Zeolite catalysts consist of silicon dioxide and aluminium oxide
• Reforming is when straight chain alkanes are turned into branched and cyclic alkanes as they burn more efficiently
• Larger chains produce more energy, however the longer the chain, more energy is needed to burn it in the first place
• In coal power station power stations, limewash is sprayed to avoid the production of sulfur dioxide, this creates calcium sulphate (gypsum) and CO2
• Since 1993, all vehicles are fitted with catalytic converters to reduce nitrous oxide and CO2 emissions
• Activities that don't release net CO2 are carbon neutral
• Alkanes are saturated hydrocarbons
• The only type of isomers alkanes can produce are chain isomers
• Alkanes do not dissolve in water because they're non polar
• Branched chain alkanes have lower boiling points as the chain have less points of contact
• In crude oil, long chain hydrocarbons are significantly less useful
• We need biofuels because:

  • The depletion of resources
  • Pollution from combustion and fossil fuels
  • Global warming and climate change
• Biodiesel and bioalchohol are not carbon neutral because or harvestry, transportation and processing of fuels
• Biodiesel is derived from plants oils such as sunflower oil and is just as efficient of a fuel at regular diesel
• The most common bioalchohol is made from the fermentation of sugar and yeast
• The issues with the production of bioalchohol are that it only creates a very small concentration and still requires separation from water