9.0 Elimination Reactions

  Alkyl Halides and Aryl Halides

• In haloalkanes, reaction with electron rich species may take place either by nucleophilic substitution or elimination. Elimination reactions, as the name suggests, are those reactions which involve the removal of atoms/ groups of atoms from two adjacent atoms in the substrate molecule.
  

• Reaction of haloalkanes with alcoholic $KOH$ forms alkenes (dehydrohalogenation reaction). These reactions are called beta-elimination because the hydrogen which is removed is present at the beta-position of the molecule.

• The order of reactivity: $R-I > R-Br > R-Cl$.
  

• Saytzeff Rule: According to this rule, whenever there is a possibility of formation of two alkenes by elimination, the formation of more substituted alkene is favored. The proton is preferentially eliminated from the carbon atom containing lesser number of hydrogen atoms.