Nucleophilic Substitution

• Halogen atoms in a C-X bond are more electronegative than C atom therefore electrons displace towards the halogen(X) and the bond is polarised
• As the Halogen gets larger, the bond strength decreases:

  1. As there is a greater atomic radius, so weaker attraction
  2. There is more shielding between nucleus and outer electrons, so weaker attraction

  Reactivity depends on bond strength: weaker = more reactive
• Nucleophiles are classified as electron pair donors, they are negatively charged ions/compounds which have an atom that has a lone pair of electrons

  
  

  e.g Hydroxide ion, OH Cynide ions, CN Ammonia ions, NH3
• Nucleophilic Reactions:

  1. With warm, aqueous Sodium Hydroxide:

  Always forms a Alcohol

  Hydroxide acts as a electron pair donor

  
• Nucleophilic Reactions:

  1. With Cynide ions in Reflux ethanolic solution

  Always forms a Nitrile

  Very important industrially, as it increases the C chain by 1

  
• Nucleophilic Reactions:

  1. With ammonia dissolved in an ethanolic solvent ammonia must be in excess
  2. ammonia initially acts as a nucleophile, electron pair donor however it forms a dative covalent bond so it has a positve charge
  3. So we react it with ammonia but it acts as a proton acceptor

  Always makes an amine