2. Reactions with halogens:
(a) Saturated hydrocarbons are inert; they do not react with bromine.
However, they do react with chlorine in the presence of light or at high temperature. These are called substitution reactions because the hydrogen atoms are substituted by chlorine atoms.
Further chlorination gives CH2C12 (methylene dichloride), CHC13 (chloroform) and CC14 (carbon tetrachloride) respectively.
(b) The unsaturated hydrocarbons undergo additional reactions.
They are more reactive because of the tendency of the doubly bonded carbon atoms to become saturated. Bromine adds to the unsaturated hydrocarbons. For example,
3. Reaction with hydrogen:
(a) Saturated hydrocarbons do not react at all with hydrogen.
(b) Unsaturated hydrocarbons react with hydrogen by adding in the presence of metal catalyst like finely divided platinum, palladium or nickel. The reaction is called catalytic hydrogenation or addition reaction. hydro