Mechanisms

• H3C


  Methyl group
• C


  Carbon atom
• H


  Hydrogen atom
• Br


  Bromine atom
• OH


  Hydroxyl group
• :Br -


  Bromide ion
• δ+


  Partial positive charge
• δ-


  Partial negative charge
• CN


  Cyanide group
• NC:


  Cyanide ion
• :OH


  Hydroxide ion
• CH3


  Methyl group
• H2O


  Water
• Br2


  Bromine molecule
• Br.


  Bromine radical
• CH3CH3


  Ethane
• HBr


  Hydrogen bromide
• CH3CH2.


  Ethyl radical
• CH3CH2Br


  Bromoethane
• CH3CH2CH2CH3


  Butane
• UV light


  Essential condition for initiation step
• STEP ONE Initiation


  Br2 → 2Br .
• STEP TWO Propagation


  CH3CH2. + Br2 → CH3CH2Br + Br.
• STEP THREE Termination


  CH3CH2. + Br. → CH3CH2Br
• Mechanism Summary for A-level AQA Chemistry
• H3C C H H Br

  Bromoethane
• H3C C H H OH

  Ethanol
• H3C C H H Br + :Br -


  δ+ δ-
• H3C C H H CN

  Ethyl cyanide (Acetonitrile)
• O


  Oxygen atom
• H3C C H H CN + :Br -


  δ+ δ-
• CH2 C H H Br

  1. Bromoethane
• H+


  Hydrogen ion (proton)
• Acid catalysed elimination mechanism: alcohols → alkenes


  The H+ comes from the conc H2SO4 or conc H3PO4
• CH2 C H H NH2

  Ethylamine
• CH2 C H H N+ CH3 H H H

  Ethylammonium ion
• 3HN: + NH4Br


  δ+ δ-
• C C H H CH3 Br H H

  1. Bromobutane
• Acid catalysed addition mechanism for hydration of ethene

  The H+ comes from the conc H3PO4
• C C H CH3 H H + Br - + H2O


  :OH-