Elimination reactions : The positive charge on carbon is propagated to the neighbouring carbon atoms by inductive effect. When moved toward by a strongest base (B), it leads to lose a proton generally from the b-carbon atom. Such reactions are named as elimination reactions. They are also E₁ and E₂ reactions.

         E₁ reaction: 

         E₂ Reaction: 

         As the above reactions involve leaving of X^- the reactivity of alkyl halides (Same alkyl group, different halogens) should be limited with C-X bond strength.

         Kind of bond                       C - I         C - Br          C - Cl

         Bond strength (kcal/mol)        45.5            54              66.5

         The dividing of the bond becomes more and more difficult and thus, the reactivity decrease.

         The sequence of reactivity (Tertiary > Secondary > Primary) is due to +I effect of the alkyl groups which increases the polarity of C -X bond.

         The primary alkyl halides undergo reactions either by S _N² or E₂ mechanisms which involve the formation of transition position. The bulky sets reason of steric hinderance in the formation of transition position. Therefore, higher homologues are not reactive than lower homologues. CH₃X > C₂H₅X > C₃H₇X, etc

         Example of elimination reaction

         (a) Dehydrohalogenation :

In that reaction, ether is a by-product as potassium ethoxide is always present in small quantity.

         (b) Action of heat :

         The decomposition chases the given sequence,

         Iodide > Bromide > Chloride      (When similar alkyl set is present) and

         Tertiary > Secondary > Primary (When similar halogen is present).

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