alkanes

• what are alkanes?

  saturated hydrocarbons with the formula cn h2n+2
• What type of bonding is involved in alkanes?

  covalent bonding, more specifically sigma bonds
• What is a sigma bond?

  It is the overlap of two orbitals between bonding atoms, it also has a direct head on overlap
• What bond angle to alkanes have around them?

  109.5 (tetrahedral)
• why does bp increase as carbon chain length increases?

  It is because there are more electrons in the compounds meaning that the london forces are stronger and harder to break. Also as molecules get larger they have a larger surface area, meaning more contact, resulting in more energy required to overcome the forced
• What happens to a molecules BP when the compound becomes branched?

  It's boiling point will decrease as there are fewer points of contact, giving fewer london forces
• Why are alkanes not very reactive?

  1 the sigma bonds are very strong

  2 the c-c bonds are non polar

  3 the electronegativity between the c and h is so similar meaning it can be considered to be non polar
• Complete combustion of alkanes?

  alkane + O2 --> CO2 + H2O
• Incomplete combustion of alkanes?

  Alkane + O2 --> CO/C +H2O
• Reactions of alkanes with Halogens (conditions)?

  UV light and heat
• What is the name for the process of adding a halogen to an alkane?

  Halogenation and substitution
• What are the three stages of the mechanism of bromination of alkanes?

  Initiation, propagation, termination.
• What is the mechanism of bromination of alkanes?

  radical substitution
• What is step 1 of radical substitution?

  Initiation- It is where the covalent bond is broken by homolytic fission, each bromine recieves 1 electron from the pair and this forms bromine radicals
• What is step 2 of radical substitution?

  Propagation- It is where it propogates through 2 propogation steps, the first is the halogen radical reacting with the alkane, and turning it into a radical, the second step is usually the alkane radical reacting with a halogen to form halogeno alkane and a halogen radical.
• What is step 3 of radical substitution?

  Termination, this is where two radicals collide to form a molecule with all electrons paired, this stops the chain reaction continuing
• What are some limitations of using radical substitution in organic synthesis?

  Further substitutions can occur, There can be differing termination products, more than one termination step, they can be at the wrong parts of the chain
• What are CFCs?


  Chlorofluorocarbons, they used to be regularly released into the atmosphere