• Organic reactions are often associated with?terminology?students should be familiar with
• Two of these important terms include:
  • Electrophilic substitution
  • Addition-elimination

Electrophilic substitution

• Electrophiles?are species that are?electron deficient?and can act as an?electron pair acceptor
  • Electrophiles are ‘electron loving’ species
• Substitution reactions?are reactions that involve the replacement of one atom or group of atoms by another
• Electrophilic substitution reactions are therefore reactions in which an atom or group of atoms are?replaced?by an?electrophile?after initial attack by the electron-deficient species
• An example of an electrophilic substitution reaction is the reaction of?benzene?with?bromine?in the presence of?anhydrous aluminium bromide catalysts
  • The bromine acts as an?electrophile?and attacks the?electron-rich benzene ring
  • A hydrogen atom is substituted by a bromine atom to form bromobenzene and hydrogen bromide
• Benzene undergoes substitution reactions rather than addition reactions because of the stability of the benzene ring

The hydrogen atom in benzene is substituted by the bromine which acts as an electrophile

Addition- elimination

• Other common organic reactions include?addition?and?elimination?reactions
• In an addition reaction, two or more molecules combine to give a?single product?only
• An example of an addition reaction is the hydrogenation of alkenes
  • Hydrogen (H₂) is reacted with an alkene to form an?alkane only?with no by-products

Hydrogenation of an alkene to give an alkane is an example of an addition reaction

• Elimination?reactions are the?reverse?of addition reactions; a?small molecule?(such as H₂O or HCl) is removed or ‘eliminated’ from an organic molecule
• An example of such a reaction is the elimination of HCl from an alkane to form an alkene

Elimination of HCl from an alkyl halide results in the formation of an alkene