L es energ ch is supplied by the energy ation by ion-dipole interaction. Step 3. The carbocation formed is step 2 can either undergo nucleophilic attack by the bisulphate 10n UIl U Cart carboca (HSOg) or may eliminate a proton. Since HSOis a very weak nucleophile, therefore, nucleophilic substitunon reaction does not occur. Instead elimination of a proton occurs to form ethylene Fast LCH,CH, CH-CH, +H (Elimination) CH CH2 tOSO,H CH,CH-OSO H (Nucleophilic substitution) The whole process is reversible. In order to shift the equilibrium towards right, strong acids and high temperatures are used when the resulting alkene being more volatile than the starting alcohol escapes from the reaction mixture.